IEC 62305-4 Lightning Protection Standard Draft

81/238/CDV
IEC/TC or SC:
Project number
Numéro de projet
Date of circulation
Date de diffusion
TC 81
CEI/CE ou SC:
COMMITTEE DRAFT FOR VOTE (CDV)
PROJET DE COMITÉ POUR VOTE (CDV)
IEC 62305-4, Ed.1
Closing date for voting (Voting
mandatory for P-members)
Date de clôture du vote (Vote
obligatoire pour les membres (P))
2003-12-19
2004-05-21
Titre du CE/SC: Protection contre la foudre
TC/SC Title: Lightning protection
Secretary: Dr. Ing. G.B. Lo Piparo (Italy)
Secrétaire: E-mail: [email protected]
Also of interest to the following committees
Intéresse également les comités suivants
Supersedes documents
Remplace les documents
SC 37A, TC 64, TC 77
81/212/CD – 81/221A/CC
Functions concerned
Fonctions concernées
Safety
Sécurité
EMC
CEM
Environment
Environnement
Quality assurance
Assurance qualité
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DOCUMENTATION.
Titre :
CEI 62305-4, Ed. 1: Protection contre la
foudre - Partie 4: Systèmes électriques et
électroniques dans des structures
Title : IEC 62305-4, Ed. 1: Protection against
lightning - Part 4: Electrical and electronic
systems within structures
Note d'introduction
Introductory note
According to the decision taken at last TC 81 meeting (see 81/236/RM item 6), National Committees are
asked (see 81/239/DC) for opinion on the following editorial proposal:
1. to delete in IEC 62305-3 the Annex B (informative): Lightning current flowing through external
conductive parts and installations entering the structure (see doc. 81/XXX/CDV)
2. to delete in IEC 62305-4 the Annex E (informative): Surges due to lightning at different installation
point(see doc. 81/238/CDV)
3. to add to IEC 62305-1 a new Annex E (informative) incorporating the Annex B of IEC 62305-3 and
the Annex E of IEC 62305-4. The proposed new Annex E of IEC 62305-1 is attached.
ATTENTION
ATTENTION
CDV soumis en parallèle au vote (CEI)
et à l’enquête (CENELEC)
Parallel IEC CDV/CENELEC Enquiry
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FORM CDV (IEC)
2002-08-09
62305-4 Ed. 1/CDV  IEC
–2–
IEC 62305-4: Protection against lightning Part 4: Electrical and electronic systems within structures
62305-4 Ed. 1/CDV  IEC
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CONTENTS
FOREWORD...........................................................................................................................6
INTRODUCTION.....................................................................................................................7
1
Scope ...............................................................................................................................9
2
Normative references .......................................................................................................9
3
Definitions ...................................................................................................................... 10
4
Design and installation of LEMP protection measures..................................................... 12
5
4.1 Basic LPM system ................................................................................................. 12
4.2 Lightning protection zones (LPZ) ........................................................................... 12
4.3 Basic protection measures in an LPM system ........................................................ 13
Earthing and bonding ..................................................................................................... 14
6
5.1 Earth termination system ....................................................................................... 14
5.2 Bonding network.................................................................................................... 15
5.3 Bonding bars ......................................................................................................... 15
5.4 Bonding at the boundary of LPZ ............................................................................ 16
5.5 Material and dimensions of bonding components................................................... 16
Magnetic shielding and line routing................................................................................. 17
7
6.1 Spatial shielding .................................................................................................... 17
6.2 Shielding of internal lines ...................................................................................... 17
6.3 Routing of internal lines......................................................................................... 17
6.4 Shielding of external lines ..................................................................................... 17
6.5 Material and dimensions of magnetic shields ......................................................... 17
Surge protective device system (SPD system) ................................................................ 18
8
Management of an LPM system ...................................................................................... 18
8.1
8.2
LPM system management plan .............................................................................. 18
Inspection of an LPM system ................................................................................. 19
8.2.1 Inspection procedure ................................................................................. 19
8.2.2 Documentation of the inspection ................................................................ 20
8.3 Maintenance.......................................................................................................... 20
TABLES ................................................................................................................................ 21
FIGURES.............................................................................................................................. 23
Annex A (informative) Basics for evaluation of electromagnetic environment in a LPZ ......... 35
A.1 Harm to electrical and electronic systems from lightning ................................................. 35
A.1.1 Source of harm...................................................................................................... 35
A.1.2 Victim of harm ....................................................................................................... 35
A.1.3 Coupling mechanisms between victim and source of harm .................................... 35
A.2 Spatial shielding, line routing and line shielding.............................................................. 36
A.2.1 General ................................................................................................................. 36
A.2.2 Grid-like spatial shields ......................................................................................... 36
A.2.3 Line routing and line shielding ............................................................................... 37
A.3 Magnetic field inside LPZ ............................................................................................... 37
A.3.1 Approximation for the magnetic field inside LPZ .................................................... 37
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A.3.2 Theoretical evaluation of the magnetic field due to direct lightning strikes ............. 41
A.3.3 Experimental evaluation of the magnetic field due to direct lightning strikes .......... 42
A.4 Calculation of induced voltages and currents .................................................................. 42
A.4.1 Situation inside LPZ 1 in case of direct lightning strikes ........................................ 42
A.4.2 Situation inside LPZ 1 in case of nearby lightning strikes ...................................... 43
A.4.3 Situation inside LPZ 2 and higher .......................................................................... 45
Annex B (informative) Implementation of LEMP protection measures in existing structures ... 59
B.1 Checklist ........................................................................................................................ 59
B.2 Integration of new electronic systems into existing structures ......................................... 59
B.2.1 Overview of possible protection measures ............................................................. 59
B.2.2 Establishment of LPZ for electrical and electronic systems .................................... 60
B.3 Upgrading of power supply and cable installation inside the structure............................ 61
B.4 Protection by surge protective devices ........................................................................... 61
B.5 Protection by isolating interfaces .................................................................................... 61
B.6 Protection measures by line routing and shielding .......................................................... 62
B.7 Upgrading of an existing LPS for spatial shielding of LPZ 1 ............................................ 62
B.8 Protection by a bonding network ..................................................................................... 63
B.9 Protection measures for externally mounted equipment .................................................. 63
B.9.1 Protection of the external equipment ..................................................................... 63
B.9.2 Reduction of overvoltages in cables ...................................................................... 63
B.10 Upgrading of interconnections between structures ........................................................ 64
B.10.1
B.10.2
Isolating lines ............................................................................................ 64
Metallic lines ............................................................................................. 64
Annex C (informative) SPD co-ordination ............................................................................. 72
C.1 General .......................................................................................................................... 72
C.2 General objective of co-ordination .................................................................................. 73
C.2.1 Co-ordination principles......................................................................................... 74
C.2.2 Co-ordination of two voltage limiting type SPD ...................................................... 74
C.2.3 Co-ordination of voltage switching type and voltage limiting type SPD................... 75
C.2.4 Co-ordination of two voltage switching type SPD ................................................... 76
C.3 Basic co-ordination variants for protection systems ........................................................ 76
C.3.1 Variant I ................................................................................................................ 76
C.3.2 Variant II ............................................................................................................... 76
C.3.3 Variant III .............................................................................................................. 77
C.3.4 Variant IV .............................................................................................................. 77
C.4 Co-ordination according to the “let through energy” method............................................ 77
C.5 Proving co-ordination ..................................................................................................... 78
Annex D (informative) Selection and installation of an SPD set…………………………… ........ 89
D.1 Selection of SPD…………………………………………………………………………….… ....... 89
D.1.1 Selection with regard to protection level……………………………………………… ... 89
D.1.2 Selection with regard to location and to discharge current…………………. ............ 89
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D.2 Installation of SPD set……………… ............................................................................... 90
D.2.1 Location of SPD… ................................................................................................ 90
D.2.2 Connecting conductors… ...................................................................................... 91
D.2.3 Protective distance l po due to oscillation phenomena… ......................................... 91
D.2.4 Protective distance l pi due to induction phenomena… ........................................... 91
D.2.5 Co-ordination of SPD…......................................................................................... 91
Annex E (informative) Surges due to lightning at different installation point……………………92
E.1 Surges due to flashes to the structure (source of damage S1)….. ................................... 92
E.2 Surges due to flashes to entering services (source of damage S3)… .............................. 92
E.3 Secondary surges downstream of SPD and due to induction effects… ............................ 92
E.3.1 Surges inside an unshielded LPZ 1….................................................................... 92
E.3.2 Surges inside shielded LPZ… ............................................................................... 90
62305-4 Ed. 1/CDV  IEC
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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Protection against lightning
Part 4: Electrical and electronic systems within structures
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising all
national electrotechnical committees (IEC National Committees). The object of the IEC is to promote international cooperation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition
to other activities, the IEC publishes International Standards. Their preparation is entrusted to technical committees;
any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International,
governmental and non-governmental organizations liaising with the IEC also participate in this preparation. The IEC
collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions
determined by agreement between the two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all interested
National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form of
standards, technical specifications, technical reports or guides and they are accepted by the National Committees in
that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International Standards
transparently to the maximum extent possible in their national and regional standards. Any divergence between the
IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment
declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62305-4 has been prepared by subcommittee WG3, of IEC technical
committee 81:
The text of this standard is based on the following documents:
FDIS
Report on voting
81/XX/FDIS
81/XX/RVD
Full information on the voting for the approval of this standard can be found in the report on voting
indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.
The committee has decided that the contents of this publication will remain unchanged until ______.
At this date, the publication will be
•
•
•
•
reconfirmed;
withdrawn;
replaced by a revised edition, or
amended.
62305-4 Ed. 1/CDV  IEC
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Protection against lightning
Part 4: Electrical and electronic systems within structures
INTRODUCTION
Lightning as a source of harm is a very high energy phenomenon. Lightning flashes release many
hundreds of mega-joules of energy, which should be contrasted with perhaps an order of magnitude
of milli-joules in sensitive electronic equipment, which might affect sensitive electronic equipment in
electrical and electronic systems within a structure.
The need for this International Standard has arisen from the increasing cost of failures of electrical
and electronic systems, caused by electromagnetic effects of lightning; particularly for the systems
used in many branches of commerce and industry, including controlling process plants of
considerable capital cost, size and complexity, for which plant outages are very undesirable for cost
and safety reasons.
Lightning can cause different types of damage in a structure as defined in IEC 62305-2:
•
D1 injuries to living beings due to touch and step voltages;
•
D2 physical damages due to mechanical, thermal, chemical and explosive effects;
•
D3 failures of electrical and electronic systems due to electromagnetic effects.
IEC 62305-3 deal with the protection measures to reduce the risk of physical damages and life
hazard and does not cover protection of electrical and electronic systems.
IEC 62305-4 therefore provides information on protection measures to reduce the risk of permanent
failures of electrical and electronic systems within structures.
Permanent failures of electrical and electronic systems can be caused by lightning electromagnetic
impulse (LEMP) by:
a) conducted and induced surges transmitted to apparatus via connecting wiring;
b) effects of radiated electromagnetic fields directly into apparatus itself.
Surges can be generated external or internal to the structure:
•
Surges external to the structure are generated by lightning flashes striking incoming lines or the
ground nearby the lines and are transmitted to electrical and electronic systems via lines itself.
•
Surges internal to the structure are generated by coupling due to lightning flashes striking the
structure or the ground nearby the structure.
The coupling can arise from different mechanisms:
•
resistive coupling (e.g. due to conventional earth impedance of earth termination system of the
structure or due to cable shield resistance);
•
magnetic field coupling (e.g. due to loops in
inductances of bonding conductors);
•
electric field coupling (e.g. due to rod antennas).
wiring of electrical and electronic systems or
Electric field coupling is generally very small compared to magnetic field coupling and can be
disregarded.
Radiated electromagnetic fields can be generated from:
62305-4 Ed. 1/CDV  IEC
–8–
•
the lightning current flowing in the lightning channel;
•
partial lightning currents flowing in conductors (e.g. in down conductors of an external LPS
according to IEC 62305-3 or in an external spatial shield according to IEC 62305-4).
The electric field component is generally very small compared to the magnetic field component and
can be disregarded.
62305-4 Ed. 1/CDV  IEC
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Protection against lightning
Part 4: Electrical and electronic systems within structures
1 Scope
This part of IEC 62305 provides information for the design, installation, inspection, maintenance
and testing of a LEMP protection system (LPM) for electrical and electronic systems within a
structure, able to reduce the risk of permanent failures due to lightning electromagnetic impulse
(LEMP).
This standard does not cover protection against electromagnetic interference due to lightning, which
may cause malfunctioning of electronic system. However the information reported in Annex A can
be used also to evaluate such disturbances. Protection measures against electromagnetic
interference are reported in IEC 60364-4-44 and IEC 61000 series.
This standard provides requirements for protection measures and guidelines for co-operation
between the designer of the electrical and electronic system and the designer of the protection
measures in order to achieve optimum protection effectiveness. This standard does not deal with
detailed design of the electrical and electronic system itself.
2 Normative references
The following normative documents contain provisions, which, through reference in this text,
constitute provisions of this International Standard. For dated references, subsequent amendments
to, or revisions of, any of these publications do not apply. However, parties to agreements based on
this International Standard are encouraged to investigate the possibility of applying the most recent
editions of the normative documents indicated below. For undated references, the latest edition of
the normative document referred to apply. Members of IEC and ISO maintain registers of currently
valid International Standards.
IEC 60364-4-43 (2001-08) and Corr.1 (2002-08): Electrical installations of buildings - Part 4-43:
Protection for safety - Protection against overcurrent
IEC 60364-4-44 (2001-08): Electrical installations of buildings - Part 4-44: Protection for safety Protection against voltage disturbances and electromagnetic disturbances
IEC 60364-5-54 (2002-06): Electrical installations of buildings - Part 5-54: Selection and erection of
electrical equipment - Earthing arrangements, protective conductors and protective bonding
conductors
IEC 60664-1 (2002-06) Ed. 1.2 Consolidated Edition: Insulation co-ordination for equipment within
low-voltage systems - Part 1: Principles, requirements and tests
IEC 61000-1-1 TR3 (1992-05): Electromagnetic compatibility (EMC) - Part 1: General - Section 1:
Application and interpretation of fundamental definitions and terms
IEC 61000-4-5 (2001-04) Ed. 1.1 Consolidated Edition: Electromagnetic compatibility (EMC) - Part
4-5: Testing and measurement techniques - Surge immunity test
IEC 61000-4-9 (2001-03) Ed. 1.1 Consolidated Edition: Electromagnetic compatibility (EMC) - Part
4-9: Testing and measurement techniques – Pulse magnetic field immunity test
IEC 61000-4-10 (2001-03) Ed. 1.1 Consolidated Edition: Electromagnetic compatibility (EMC) - Part
4-10: Testing and measurement techniques - Damped oscillatory magnetic field immunity test
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IEC 61000-5-2 TR3 (1997-11): Electromagnetic compatibility (EMC) - Part 5: Installation and
mitigation guidelines - Section 2: Earthing and cabling
IEC 61000-5-6 TR (2002-06): Electromagnetic compatibility (EMC) - Part 5-6: Installation and
mitigation guidelines - Mitigation of external EM influences
IEC 62305-1 Ed. 1.0: Protection against lightning. Part 1: General principles
IEC 62305-2 Ed. 1.0: Protection against lightning. Part 2: Risk management
IEC 62305-3 Ed.1.0: Protection against lightning. Part 3: Physical damage to structures and life
hazard
IEC 61643-1 Ed. 1.1 (2002-01): Surge protective devices connected to low-voltage power
distribution systems - Part 1: Performance requirements and testing methods
IEC 61643-12 (2002-02): Low-voltage surge protective devices - Part 12: Surge protective devices
connected to low-voltage power distribution systems - Selection and application principles
IEC 61643-21 (2000-09) Ed. 1.0: Low voltage surge protective devices - Part 21: Surge protective
devices connected to telecommunications and signalling networks - Performance requirements and
testing methods
IEC 61643-22 Ed. 1.0: Surge protective devices connected to telecommunications and signalling
networks - Part 22: Selection and application principles (DRAFT)
IEC 62066 TR (2002-06): Surge overvoltages and surge protection in low-voltage a.c. power
systems - General basic information
ITU-T Recommendation K.20 (2000-02): Resistibility of telecommunication equipment installed in a
telecommunications centre to overvoltages and overcurrents
ITU-T Recommendation K.21 (2000-10): Resistibility of telecommunication equipment installed in
customer's premises to overvoltages and overcurrents
3 Definitions
For the purpose of this document, the following definitions apply as well as those given in other
parts of IEC 62305:
3.1 Electrical system
A system incorporating low voltage power supply components and possibly also electronic
components
3.2 Electronic system
A system incorporating sensitive electronic components such as information technology equipment,
control and instrumentation systems, radio systems, power electronic installations
3.3 Internal system
Electrical and electronic system to be protected in and on a structure
3.4 Lightning electromagnetic impulse (LEMP)
Electromagnetic effects of lightning current.
NOTE – It includes conducted surges as well as radiated impulse electromagnetic field effects.
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3.5 Surges
Transient wave appearing as overvoltages and /or overcurrents
NOTE – Surges caused by LEMP can arise from (partial) lightning currents, from induction effects into installation loops
and as remaining threat downstream of SPD.
3.6 Rated impulse withstand voltage level (U w)
An impulse withstand voltage assigned by the manufacturer to the equipment or to a part of it,
characterising the specified withstand capability of its insulation against overvoltages
3.7 Lightning protection level (LPL)
Number related to a set of lightning current parameters values relevant to the probability that the
associated maximum and minimum design values will not be exceeded in naturally occurring
lightning.
NOTE - Lightning protection level is used to design protection measures according to the relevant set of lightning current
parameters
3.8 Lightning protection zone (LPZ)
Zone where the lightning electromagnetic environment is defined
3.9 LEMP protection system (LPM)
Complete system of protection measures for internal systems against LEMP
3.10 Grid-like spatial shield
Magnetic shield characterised by openings
NOTE - For a building or a room it is preferably built by interconnected natural metal components of the structure (e.g.
rods of reinforcement in concrete, metal frames and metal supports).
3.11 Earth termination system
Part of an external LPS which is intended to conduct and disperse lightning current into the earth
3.12 Bonding network
Interconnecting network of all conductive parts of the structure and of internal systems (live
conductors excluded) to the earth termination system
3.13 Earthing system
Complete system combining the earth termination system and the bonding network
3.14 Surge protective device (SPD)
Device that is intended to limit transient overvoltages and divert surge currents. It contains at least
one non linear component
3.15 Class I tested SPD
SPD tested according to Class I test procedure)
3.16 Class II tested SPD
SPD tested according to Class II test procedure
3.17 Class III tested SPD
SPD tested according to Class III test procedure
3.18 SPD - voltage switching type
SPD that has a high impedance when no surge is present, but can have a sudden change in
impedance to a low value in response to a voltage surge
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NOTE 1 - Common examples of components used as voltage switching devices are: spark gaps, gas discharge tubes
(GDT), thyristors (silicon-controlled rectifiers) and triacs. These SPD are sometimes called "crowbar type“.
NOTE 2 - A voltage switching device has a discontinuous voltage/current characteristic.
3.19 SPD - voltage limiting type
SPD that has a high impedance when no surge is present, but will reduce it continuously with
increased surge current and voltage
)
NOTE 1 - Common examples of components used as non-linear devices are: varistors and suppressor diodes. These
SPDs are sometimes called "clamping type“.
NOTE 2 - A voltage limiting device has a continuous voltage/current characteristic.
3.20 SPD - combination type
SPD that incorporates both voltage switching type components and voltage limiting type
components may exhibit voltage switching, voltage limiting or both voltage switching and voltage
limiting behaviour depending upon the characteristics of the applied voltage
3.21 Surge protective device set (SPD set)
set of SPD properly selected, co-ordinated and erected used to reduce failures of electrical and
electronic systems
4
Design and installation of LEMP protection measures
Electrical and electronic systems are endangered by the lightning electromagnetic impulse (LEMP).
Therefore LEMP protection measures shall be provided to avoid failures of internal systems.
Protection against LEMP is based on the lightning protection zones (LPZ) concept: the volume
containing systems in need of protection shall be divided into LPZ. These zones are theoretically
assigned volumes of space where the LEMP severity is compatible with the immunity level of the
internal systems enclosed (see Figure 1). Successive zones are characterized by significant
changes in the LEMP severity.
4.1 Basic LPM system
A full LPM system (Figure 2a) will protect against conducted surges as well as against radiated
magnetic fields.
NOTE 1 – For risk management, failure of apparatus due to electromagnetic fields directly radiated into its is negligible
provided that apparatus comply with relevant EMC immunity product standard.
A minimum LPM system (Figure 2b) is suitable for apparatus which is insensitive to radiated
magnetic fields. Its surge protective device (SPD) set will protect apparatus against conducted
surges only.
NOTE 2 – An LPS according to IEC 62305-3 gives no effective protection against failures of electrical and electronic
systems (Figure 2c).
4.2 Lightning protection zones (LPZ)
With respect to the lightning threat the following LPZ are defined (see IEC 62305-1):
Outer zones
LPZ 0
Endangered by the unattenuated lightning electromagnetic field and by surges up to
full or partial lightning current. LPZ 0 is subdivided into:
LPZ 0 A
Endangered by direct lightning strikes, by up to full lightning current surges and by
full lightning electromagnetic field.
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LPZ 0 B
Protected against direct lightning strikes. Endangered by surges up to partial
lightning current surges and by full lightning electromagnetic field.
Inner zones
(Protected against direct lightning strikes)
LPZ 1
Surges limited by current sharing and by SPD at the boundary.
Lightning field can be attenuated by spatial shielding.
LPZ 2 ... n
Surges further limited by current sharing and SPD at the boundary.
Lightning field usually attenuated by spatial shielding.
Depending on number, type and withstand level of the equipment to be protected, suitable LPZ can
be defined, from small local zones (down to the housing of a single equipment) up to large integral
zones (finally extended to the whole structure volume). For examples see Figure B.2.
Interconnection of LPZ of the same order either could be needed if two separate structures are
connected by electrical or signal lines, or could be used to reduce the number of required SPD
(Figure 3).
Extending an LPZ into another LPZ might be needed in special cases or can be used, to reduce the
number of required SPD (Figure 4).
Detailed information on evaluation of electromagnetic environment in LPZ is reported in Annex A.
4.3 Basic protection measures in an LPM system
Basic protection measures against LEMP include:
4.3.1 Earthing and bonding, complying with 5;
Earthing measures conduct and disperse the lightning current into the earth.
Bonding measures minimise potential differences and may reduce magnetic field.
4.3.2
Magnetic shielding and line routing, complying with 6;
Spatial shielding attenuates the magnetic field inside LPZ arising from lightning strikes to or
nearby the structure and reduces internal surges.
Spatial shielding affects the following risk components (IEC 62305-2):
RB
physical damage due to flashes to the structure (valid for shield of LPZ 1 only);
RC
failures due to flashes to the structure;
RM
failures due to flashes near to the structure.
Shielding of internal lines using shielded cables or cable ducts minimises internal surges induced
into the installation.
Shielding of internal lines affects the following risk components (IEC 62305-2):
failures due to flashes to the structure;
RC
RM
failures due to flashes near to the structure.
Routing of internal lines can minimise induction loops and reduce internal surges.
Routing of internal lines affects the following risk components (IEC 62305-2):
RC
failures due to flashes to the structure;
RM
failures due to flashes near to the structure.
NOTE - Spatial shielding, shielding and routing of internal lines can be combined or used separately.
Shielding of external lines incoming into the structure reduces external surges conducted to the
connected electrical and electronic system.
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Shielding of incoming lines affects the following risk components (IEC 62305-2):
RV
physical damage due to flashes to an incoming line;
RW failures due to flashes to an incoming line;
RZ
failures due to flashes near to an incoming line.
4.3.3 Surge protective device set (SPD set), complying with 7;
The surge protective device set limits external and internal surges.
Surge protective device set affects the following risk components (IEC 62305-2):
RB
physical damage due to flashes to the structure (valid for SPD at LPZ 1 entrance);
physical damage due to flashes to an incoming line (valid for SPD at LPZ 1 entrance);
RV
RC
failures due to flashes to the structure;
RM
failures due to flashes near to the structure;
RW failures due to flashes to an incoming line;
RZ
failures due to flashes near to an incoming line.
Earthing and bonding shall always be provided, in particular, bonding of every conductive service,
directly or via an SPD, at the point of entry to the structure. The other LEMP protection measures
can be used alone or in combination.
LEMP protection measures shall withstand the stress, e.g. stress of temperature, humidity,
corrosive atmosphere, vibration, voltage and current expected in the installation place.
The performance of LEMP protection measures is reported in IEC 62305-2, Annex B. Selection of
the most suitable LEMP protection measures shall be made by risk assessment according to IEC
62305-2, taking into account technical and economic factors.
For implementation of LEMP protection measures see also IEC 60364-4-44. Further practical
information on implementation in existing structures are reported in Annex B.
5 Earthing and bonding
Suitable earthing and bonding is based on a complete earthing system (Figure 5) combining
•
the earth termination system (dispersing the lightning current into the soil), and
•
the bonding network (minimising potential differences and reducing the magnetic field).
5.1 Earth termination system
The earth termination system of the structure shall comply with IEC 62305-3. In structures where
only robust electrical systems are provided, type A earthing arrangement may be used, but type B
earthing arrangement is preferable. In structures with sensitive electronic systems an earthing
arrangement type B is required.
The ring earth electrode around the structure or the ring earth electrode in the concrete at the
perimeter of the foundation, should be integrated with a meshed network under and around the
structure with a mesh width of typically 5 m. This greatly improves the performance of the earth
termination system. The reinforcement of the concrete in the floor of the basement of the structure,
which forms a well defined interconnected mesh, connected to the earth termination system
typically every 5 m performs such function too. An example of a meshed earth termination system of
a plant is shown in Figure 6.
To reduce potential differences between internal systems bonded to separate earthing systems,
structures interconnected by cables shall have interconnected earthing systems preferably with
many parallel conductors in same paths as the cables. Potential differences are reduced by
62305-4 Ed. 1/CDV  IEC
– 15 –
enclosing cables in grid-like reinforced concrete ducts or in continuously bonded metal conduits
integrated into the interconnected earth termination system.
Use of shielded cables with shield of adequate thickness, bonded to earthing systems at both ends,
can reduce such potential differences to negligible values.
5.2 Bonding network
A low impedance bonding network is needed to avoid dangerous potential differences between all
equipment inside the inner LPZ. Moreover such bonding network also reduces the magnetic field
(see Annex A).
This can be realised by a meshed bonding network integrating any conductive parts of the structure
or parts of the internal system and by bonding all metal parts or conductive services at the
boundary of each LPZ directly or by suitable SPD.
It can be set up as a three-dimensional, meshed, bonding network (Figure 5) with a typical mesh
width of 5 m. This requires multiple interconnection of all metal components in and on the structure
(such as reinforcement of concrete, elevator rails, cranes, metal roofs, metal facades, metal frames
of windows and doors, metal floor frames, service pipes, cable trays). In the same way also the
bonding bars (e.g. ring bonding bars, several bonding bars at different structure's level) and the
magnetic shields of the LPZ shall be integrated.
Examples for bonding networks are shown in figures 7 and 8.
Conductive parts (cabinets, housing, rack) and the protective conductor PE of the electrical and
electronic system shall be earthed by being bonded to the bonding network according to the
following configurations (Figure 9):
•
Star configuration S
•
Meshed configuration M.
If the configuration S is used, all metal components of the electrical and electronic system shall be
isolated adequately from the earthing system. The configuration S shall be integrated into the
earthing system only by a single bonding bar acting as earthing reference point (ERP) resulting in
type S s . When configuration S is used, all lines between the individual equipment shall run in
parallel with the bonding conductors following the star configuration in order to avoid induction
loops. Configuration S can be used where electrical and electronic systems are locally confined in
relatively small zones and all lines enter the zone at one point only.
If configuration M is used, the metal components of the electrical and electronic systems are not to
be isolated from the earthing system, but shall be integrated into it by multiple bonding points,
resulting in type M m . Configuration M is to be preferred for electrical and electronic systems
extended in relatively wide zones or to a whole structure, where many lines run between the
individual equipment, and where the lines enter the structure at several points.
In complex systems, the advantages of both configurations (configuration M and S) can be
combined as illustrated in Figure 10, resulting in combination 1 (S s combined with M m ) or in
combination 2 (M s combined with M m ).
5.3 Bonding bars
Bonding bars shall be installed for bonding of
•
all conductive services entering a LPZ (directly or by suitable SPD),
62305-4 Ed. 1/CDV  IEC
– 16 –
•
the protective conductor PE,
•
metal components of the internal systems (e.g. cabinets, housings, racks)
•
the magnetic shields of the LPZ at the periphery and inside the structure.
For efficient bonding the following installation rules are important (see also Figure 11):
•
the basis for all bonding measures is a low impedance bonding network
•
bonding bars should be connected to the earthing system by shortest possible way (by
bonding conductor not longer than 1 m)
•
material and dimensions of bonding bars and bonding conductors comply with 5.5
•
SPD should use shortest possible connections to the bonding bar as well as to the live
conductors thus minimising inductive voltage drops
•
on the protected side of the circuit following an SPD, mutual induction effects should be
minimised, either by minimising the loop area or using shielded cables or cable ducts.
5.4 Bonding at the boundary of LPZ
Where an LPZ is defined, bonding shall be provided for all metal parts and services (e.g. metal
pipes, power lines or signal lines) penetrating the boundary of LPZ.
NOTE - Bonding of services entering LPZ 1 should be discussed with the network providers involved (e.g. electrical power
or telecommunication authorities), because there could be conflicting requirements.
Bonding shall be performed via bonding bars, which are installed as close as possible to the
entrance point at the boundary.
Incoming services should enter the LPZ at the same location and be connected to the same
bonding bar. If services enter the LPZ at different locations, a ring bonding bar is recommended.
SPD are always required at the entrance of the LPZ to bond incoming lines connected to electrical
and electronic systems within LPZ. The number of required SPD can be reduced using
interconnected or extended LPZ.
Shielded cables or interconnected metal cable ducts, bonded at each LPZ boundary, can be used
either to interconnect several LPZ of the same order to one joint LPZ, or to extend a LPZ until the
next boundary.
5.5 Material and dimensions of bonding components
Material, dimensions and conditions of use shall comply with IEC 62305-3.
The minimum cross-section for bonding components shall comply with Table 1.
Clamps shall be dimensioned considering the lightning current values according to LPL (see IEC
62305-1) and the current sharing analysis (see Annex B of IEC 62305-3).
SPD shall be dimensioned according to 7.
62305-4 Ed. 1/CDV  IEC
– 17 –
6 Magnetic shielding and line routing
Magnetic shielding reduces the electromagnetic field as well as induced internal surges. Suitable
routing of internal lines can minimise induced internal surges. Both measures are effective against
permanent failures of electrical and electronic systems.
6.1 Spatial shielding
Spatial shields define protected zones, covering the whole structure, a part of it, a single room or
the housing of apparatus only. Grid-like or continuous metallic shields are used in this case,
preferably utilising "natural components" of the structure (see IEC 62305-3).
Spatial shields are advisable, where it is more practical and useful to protect a defined zone of the
structure instead of several apparatuses individually. Spatial shields should be provided in the early
planning stage of a new structure or a new internal system, because for existing installations higher
cost and greater technical difficulties may arise.
6.2 Shielding of internal lines
Shielding may be restricted to cabling and equipment of the system to be protected: metallic shield
of cables, closed metallic cable duct and metallic enclosure of equipment are used for this purpose.
6.3 Routing of internal lines
Suitable routing of internal lines minimises induction loops and reduces internal surges. The loop
area can be minimised by routing of cables close to earthed natural components of the structure
and by adjacent routing of electrical and signal lines (Otherwise some distance between power lines
and unshielded signal lines can be needed, in order to avoid interference).
6.4 Shielding of external lines
Shielding of external lines entering into the structure includes: cable shields, closed metallic cable
ducts or concrete cable ducts with interconnected reinforcement. Shielding of external lines is
helpful, but often not within the responsibility of the LPM system planner (The owner of external
lines is mostly the network provider).
6.5 Material and dimensions of magnetic shields
At boundary of zones LPZ 0 A /1 materials and dimensions of magnetic shields (e.g. grid-like spatial
shield, cable shield, equipment’s cabinet) shall comply with the requirements of IEC 62305-3 for airtermination conductors and/or down conductors. In particular:
•
Minimum thickness of metal sheets, metal ducts, piping and cable shield shall comply with
IEC 62305-3, Table 3;
•
Configuration and minimum cross-section of conductors of grid-like spatial shield shall
comply with IEC 62305-3, Table 6;
Compliance of magnetic shields with IEC 62305-3,Table 3 and Table 6, is not required:
•
at boundary of zones LPZ 1/2 or higher, provided that the separation distance s between
magnetic shields and LPS is respected (see IEC 62305-3, Clause 6.3);
•
at boundary of any LPZ, if the frequency N d of lightning flashes to the structure is estimated
negligible, i.e. N d < 0,1.
62305-4 Ed. 1/CDV  IEC
– 18 –
7 Surge protective device set (SPD set)
The protection of internal systems against surges may require an SPD set consisting of a coordinated set of SPD. The principles for selection and installation of an SPD set are the same for
electrical and electronic systems. But because of the high diversity of electronic systems
characteristics (analog or digital, d.c. or a.c. from low to high frequency), rules for selection and
erection of an SPD set are different from those relevant to electrical systems.
In a full LPM using the lightning protection zones concept with more than one LPZ (LPZ 1, LPZ 2
and higher), SPD shall be located at the line entrance into each LPZ (see also Figure 2). In a
minimum LPM using LPZ 1 only, SPD shall be located at least at the line entrance into LPZ 1. In
both cases additional SPD can be required, if the distance between the location of the SPD and the
apparatus to be protected becomes too long.
Selection and erection of the SPD set shall comply with:
•
IEC 61643-12 and IEC 60364-5-53 for protection of power systems;
•
IEC 61643-22 for protection of telecommunications and signalling systems.
SPD set for low voltage power systems should comply also with the requirements given in Annex D.
Information on surges due to lightning for dimensioning of SPD at different installation points are
given in Annex E.
8 Management of an LPM
For new structures, to reach an efficient protection with the minimum cost investment, it is
necessary that the design of electrical and electronic system be carried out during the building
design stage and before construction. In this way it is possible to optimise the use of the natural
components of structure and to choose the best compromise in the cabling layout and equipment
positioning with reference to the possible acceptable alternatives.
For existing structures the cost of LPM is generally higher than that for new structures. However it
is possible to minimise the investment cost by a proper choice of LPZ and by using or upgrading of
existing installations.
Proper protection can be achieved only if:
•
provisions are defined by a lightning protection expert;
•
good co-ordination is made between the different experts involved in building construction
and in LEMP protection measures (e.g. civil and electrical engineers);
•
the management plan of 8.1 is followed.
The LPM shall be maintained by inspection and maintenance. After relevant changes to the
structure or to the protection measures, a new risk assessment shall be performed.
8.1 LPM management plan
Planning and co-ordination of an LPM requires a management plan (Table 2). It starts with an initial
risk assessment (IEC 62305-2) to determine the required protection measures to reduce risk to or
below the tolerable level. To do it the lightning protection zones shall be fixed.
62305-4 Ed. 1/CDV  IEC
– 19 –
According to LPL (IEC 62305-1) of protection measures to be adopted the following steps shall be
made:
•
an earthing system (bonding network and earth termination system) shall be provided;
•
external metal parts and incoming services shall be bonded directly or by suitable SPD;
•
the internal system shall be integrated into the bonding network;
•
spatial shielding in combination with line routing and shielding can be implemented;
•
requirements for an SPD set shall be determined;
•
for existing structures special measures could be needed (Annex B).
The cost/benefit relation for the selected protection measures should be optimised using again the
risk assessment method.
8.2 Inspection of an LPM
The inspection comprises checking of technical
measurements. Scope of inspection is to verify that:
documentation,
visual
inspections
•
the LEMP protection measures comply with the design,
•
the LEMP protection measures are capable of performing their design functions,
•
any new added protection measure is integrated correctly into the LPM.
and
Inspections shall be made:
•
during the installation of the LPM,
•
after the installation of the LPM,
•
periodically,
•
after any alteration of components relevant to LPM,
•
possibly after a lightning flash to the structure (e.g. identified by a lightning counter).
The frequency of the periodical inspections shall be fixed considering:
•
the local environment, such as corrosive soil and atmosphere,
•
the type of protection measures used.
8.2.1 Inspection procedure
8.2.1.1 Checking of technical documentation
After the installation of a new LPM, the technical documentation shall be checked for compliance
with the relevant standards, and for completeness. Subsequently the technical documentation shall
be continuously updated, e.g. after any alteration or extension of the LPM.
62305-4 Ed. 1/CDV  IEC
– 20 –
8.2.1.2 Visual inspection
Visual inspection shall be made to verify that:
•
there are no loose connections and no accidental breaks in conductors and joints;
•
no part of the system has been weakened by corrosion, especially at ground level;
•
bonding conductors and cable shields are intact;
•
there are no additions or alterations which require additional protection measures;
•
there is no indication of damage to SPD and their fuses;
•
line routing is maintained;
•
safety distances to the spatial shields are maintained.
8.2.1.3
Measurements
For those parts, which are not visible for inspection, measurements of electrical continuity should
be performed.
8.2.2 Documentation of the inspection
A guide for inspection should be prepared to facilitate the process. The guide should contain
sufficient information to lead the inspector through the task, so that all aspects of installation and
components, tests methods and test data recorded can be documented.
The inspector shall prepare a report, which shall be attached to the technical documentation and
the previous inspection reports. The inspection report shall contain information concerning:
•
the general status of the LPM,
•
any deviation from the technical documentation,
•
the results of measurements performed.
8.3 Maintenance
After the inspection all defects detected shall be repaired without delay. If necessary, the technical
documentation shall be updated.
62305-4 Ed. 1/CDV  IEC
– 21 –
TABLES
Table 1 - Minimum cross-sections for bonding components
Bonding component
Material
Bonding bars (Copper or galvanised steel)
Connecting conductors from bonding bars
to the earthing system or to other bonding bars
Connecting conductors from internal metal
installations to bonding bars
Connecting conductors for SPD
Class I
NOTE – Other material used instead of
copper shall have equivalent crosssection.
Class II
Class III
Cross-section
mm
Cu, Fe
50
Cu
14
Al
22
Fe
50
Cu
5
Al
8
Fe
16
5
Cu
3
1
2
62305-4 Ed. 1/CDV  IEC
– 22 –
Table 2 - LPM management plan for new buildings and
for extensive changes in construction or use of buildings
Step
Initial risk analysis
Aim
1)
Final risk analysis 1)
Action to be taken by
Checking the need for LEMP protection.
- Lightning protection expert 2)
If needed, selection of suitable LPM using
the risk assessment method.
- owner
The cost/benefit relation for the selected
protection measures should be optimised
using again the risk assessment method.
As result are defined:
- Lightning protection expert 2)
- owner
- LPL and the lightning parameters
- LPZ and their boundaries
LPM planning
Definition of LPM:
- Lightning protection expert
- spatial shielding measures
- owner
- bonding networks
- architect
- earth termination systems
- planners of internal systems
- line shielding and routing
- planners of relevant installations
- shielding of incoming services
- SPD system
LPM design
General drawings and descriptions
- Engineering office or equivalent
Preparation of lists for tenders
Detailed drawings and time tables for the
installation
Installation of LPM
including supervision
Quality of installation
- Lightning protection expert
Documentation
- installer of the LPM
Possibly revision of the detailed drawings
- engineering office
- supervisor
Approval of LPM
Checking and documentation of the state
of the system
- Independent lightning protection
expert
- supervisor
Recurrent inspections
Ensuring the adequacy of the LPM
- Lightning protection expert
- supervisor
1)
See IEC 62305-2.
2)
With a broad knowledge of EMC and knowledge of installation practices.
62305-4 Ed. 1/CDV  IEC
– 23 –
FIGURES
LPZ 0
Antenna
Mast
or
railing
Electrical
power line
Boundary
of
LPZ 2
LPZ 2
LPZ 1
Boundary
of
LPZ 1
Equipment
Water
pipe
Bonding
location
Telecommunication
line
Bonding of incoming services directly or by suitable SPD
This Figure shows an example for dividing a structure into inner LPZ. All metal services entering the structure are bonded
via bonding bars at the boundary of LPZ 1. In addition, the metal services entering LPZ 2 (e.g. computer room) are
bonded via bonding bars at the boundary of LPZ 2.
Figure 1 - General principle for the division into different LPZ
62305-4 Ed. 1/CDV  IEC
– 24 –
Shield LPZ 1
I0 , H0
LPZ 0
LPZ 1
Shield LPZ 2
Shield (Housing)
H1
H2
LPZ 2
Apparatus
(victim)
H0
SPD
SPD 1/2
U1 , I1
U2 , I2
SPD 0/1
U0 , I0
Partial
lightning
current
Figure 2a – Full LPM according to IEC 62305-4: Apparatus protected
against conducted surges as well as against radiated magnetic fields
LPS (No shielding)
I0 , H0
LPZ 0
LPZ 1
H0
H0
H0
Apparatus
(victim)
Shield (Housing)
SPD (SA)
SPD (SB)
SPD (MB)
U2 , I2
U1 , I1
U0 , I0
Partial
lightning
current
Figure 2b – Minimum LPM according to IEC 62305-4: Apparatus protected
against conducted surges, but not against radiated magnetic fields.
LPS (No shielding)
I0 , H0
LPZ 0
LPZ 1
H0
H0
H0
Apparatus
(victim)
Shield (Housing)
SPD (MB)
U1 , I1
U0 , I0
Partial
lightning
current
Figure 2c – LPS according to IEC 62305-3: Apparatus has no effective protection either
against conducted surges or against radiated magnetic fields.
Figure 2 – Protection against LEMP
62305-4 Ed. 1/CDV  IEC
– 25 –
a
b
i1 , i 2
partial lightning currents
Figure 3a, 3b – Interconnecting two LPZ 1
a) using SPD
b) using shielded cables or shielded cable ducts
Figure 3a shows two LPZ 1 connected by electrical or signal lines. Special care should be taken, if both LPZ 1 represent
separate structures with separate earthing systems, spaced tens or hundreds of meters from each other. In this case a
large part of the lightning current can flow along the connecting lines, which are not protected.
Figure 3b shows, that this problem can be solved using shielded cables or shielded cable ducts to interconnect both LPZ
1, provided that the shields are able to carry the partial lightning current. The SPD can be omitted, if the voltage drop
along the shield is not too high.
62305-4 Ed. 1/CDV  IEC
– 26 –
c
d
c), d) – Interconnecting two LPZ 2
c) using SPD
d) using shielded cables or shielded cable ducts
Figure 3c shows two LPZ 2 connected by electrical or signal lines. Because the lines are exposed to the threat level of
LPZ 1, SPD at the entry into each LPZ 2 are required.
Figure 3d shows that such interference can be avoided and the SPD can be omitted, if shielded cables or shielded cable
ducts are used to interconnect both LPZ 2.
Figure 3 – Examples for interconnected lightning protection zones
62305-4 Ed. 1/CDV  IEC
a
– 27 –
b
Figure 4a shows a structure powered by a transformer. If the transformer is placed outside the structure, only the low
voltage lines entering the structure need protection by SPD. If the transformer should be placed inside the structure, the
owner of the building often is not allowed to adopt protection measures on the high voltage side.
Figure 4a – Transformer outside the structure
Figure 4b shows that the problem can be solved extending LPZ 0 into LPZ 1, which requires again SPD at the low voltage
side only .
Figure 4b – Transformer inside the structure (LPZ 0 extended into LPZ 1)
c
d
Figure 4c shows an LPZ 2 supplied by an electrical or signal line. This line needs two co-ordinated SPDs: one at the
boundary of LPZ 1, the other at the boundary of LPZ 2.
Figure 4c – Two co-ordinated SPD (0/1) and SPD (1/2) needed
Figure 4d shows that the line can enter immediately into LPZ 2 and only one SPD is required, if LPZ 2 is extended into
LPZ 1 using shielded cables or shielded cable ducts. However this SPD shall reduce the threat immediately to the level of
LPZ 2.
Figure 4d – Only one SPD (0/1/2) needed (LPZ 2 extended into LPZ 1)
62305-4 Ed. 1/CDV  IEC
– 28 –
Figure 4 – Examples for extended lightning protection zones
Bonding
network
Earth termination system
All drawn connections are either bonded structure metal elements or bonding connections. Some of them may also serve
to intercept, conduct and disperse the lightning current into the earth.
Figure 5 – Example of a three-dimensional earthing system
consisting of the bonding network interconnected with the earth termination system
62305-4 Ed. 1/CDV  IEC
1
2
3
4
– 29 –
building with meshed network of the reinforcement
tower inside the plant
stand-alone equipment
cable tray
Figure 6 - Meshed earth termination system of a plant
62305-4 Ed. 1/CDV  IEC
– 30 –
1
2
3
4
5
6
7
8
9
10
11
air termination conductor
metal covering of the roof parapet
steel reinforcing rods
mesh conductors superimposed on the reinforcement
joint of the mesh conductor
joint for an internal bonding bar
connection by welding or clamping
arbitrary connection
steel reinforcement in concrete (with superimposed mesh conductors)
ring earth electrode (if any)
foundation earth electrode
a
b
typical distance of 5 m for superimposed mesh conductors
typical distance of 1 m for connecting this mesh with the reinforcement
Figure 7 – Utilising the reinforcing rods of a structure for equipotential bonding
62305-4 Ed. 1/CDV  IEC
1
2
3
4
5
6
7
8
9
– 31 –
electrical power equipment
steel girder
metal covering of the facade
bonding joint
electrical or electronic equipment
bonding bar
steel reinforcement in concrete (with superimposed mesh conductors)
foundation earth electrode
common inlet for different services
Figure 8 – Equipotential bonding in a structure with a steel reinforcement
62305-4 Ed. 1/CDV  IEC
– 32 –
Star configuration
S
Meshed configuration
M
Basic
configuration
Integration
into
bonding
network
Bonding network
Bonding conductor
Equipment
Bonding point to the bonding network
ERP
Earthing reference point
Ss
Star point configuration integrated by star point
Mm
Meshed configuration integrated by mesh
Figure 9 - Integration of electronic systems into the bonding network
62305-4 Ed. 1/CDV  IEC
– 33 –
Combination 1
Combination 2
Integration
into
bonding
network
Bonding network
Bonding conductor
Equipment
Bonding point to the bonding network
ERP
Earthing reference point
Ss
Star point configuration integrated by star point
Mm
Meshed configuration integrated by mesh
Ms
Meshed configuration integrated by star point
Figure 10 - Combinations of integration methods of electronic systems
into the bonding network
62305-4 Ed. 1/CDV  IEC
– 34 –
Live conductor
U
∆U
I
Loop
area
UP
H , dH/dt
∆U
Bonding bar
I
Partial lightning current
U
Surge voltage between live conductor and bonding bar
UP
Limiting voltage of SPD
∆U
Inductive voltage drop on the bonding conductors
H, dH/dt
Magnetic field and its time derivative
The surge voltage U between the live conductor and the bonding bar is higher than the protection level U p of the SPD,
because of the inductive voltage drops ∆U at the bonding conductors (even if the maximum values of U P and ∆U do not
necessarily appear simultaneously). Moreover, the partial lightning current flowing through the SPD induces additional
voltage into the loop on the protected side of the circuit following the SPD. Therefore the maximum voltage endangering
the connected equipment can be considerably higher then the protection level U P of the SPD.
Figure 11 - Surge voltage between live conductor and bonding bar
62305-4 Ed. 1/CDV  IEC
– 35 –
Annex A
(informative)
Basics for evaluation of electromagnetic environment in a LPZ
This Annex supplies information for evaluation of electromagnetic environment inside LPZ, which
can be used for protection against LEMP, but also for protection against electromagnetic
interference.
A.1
Harm to electrical and electronic systems from lightning
A.1.1
Source of harm
The primary source of harm is the lightning electromagnetic impulse (LEMP), especially the
lightning current and its unattenuated magnetic field, which has the same waveshape as the
lightning current.
NOTE - For protection considerations the influence of the lightning electric field is usually of minor interest.
A.1.2
Victim of harm
The victims of harm are internal systems installed in or on a structure, which have only a limited
inherent immunity against damage due to surges and due to magnetic fields.
Systems outside on a structure may be endangered by the unattenuated magnetic field and
possibly, if positioned in an exposed location, by lightning flashes to the structure.
Systems inside a structure are endangered by the remaining attenuated magnetic field, by induced
internal surges and by external surges transmitted by incoming lines.
For details concerning the immunity of systems to be protected refer to relevant standards:
•
The immunity of the installation is defined in IEC 60664-1:
Immunity level defined by the rated impulse withstand voltage 1,5-2,5-4-6 kV.
•
The immunity of apparatus is defined by test procedures in IEC 61000-4:
The immunity against conducted surges is provided by a test according to IEC 61000-4-5 with
test levels for voltage: 0,5-1-2-4 kV at 1,2/50 waveshape respectively for current: 0,25-0,5-1-2
kA at 8/20 waveshape
The immunity against magnetic fields is provided by tests according to IEC 61000-4-9 with test
levels: 100-300-1000 A/m at 8/20 waveshape and IEC 61000-4-10 (Test levels: 10-30-100 A/m
at 1MHz).
•
The immunity of telecommunication equipment is defined in ITU-T K.20 and K.21
NOTE – Equipment, which meets the immunity requirements of the standards above, can contain internal SPD. The
characteristics of these internal SPD can affect the co-ordination.
A.1.3
Coupling mechanisms between victim and source of harm
The victim of harm with its immunity level has to be made compatible with the source of harm. For
this the coupling mechanisms are to be adequately controlled. This is achieved by the
implementation of individually co-ordinated lightning protection zones (LPZ).
62305-4 Ed. 1/CDV  IEC
A.2
A.2.1
– 36 –
Spatial shielding, line routing and line shielding
General
The magnetic field caused inside LPZ by lightning flashes to the structure or to ground nearby the
structure can be reduced only by spatial shielding of the LPZ. Voltages and currents induced into
the electronic system can be minimised either by spatial shielding or by line routing and shielding or
by combining both methods.
Figure A.1 gives an example of the LEMP situation in the case of lightning strike, showing a
structure with the lightning protection zones LPZ 0, LPZ 1 and LPZ 2. The system to be protected is
installed inside LPZ 2.
The primary electromagnetic source of harm to the electronic system is the lightning current I 0 and
the magnetic field H 0 . Along incoming services flow partial lightning currents. These currents as well
as the magnetic field have the same waveshape. The lightning current to be considered here
consists of a first stroke I f (10/350 waveshape) and subsequent strokes I s (0,25/100 waveshape).
The current of the first stroke I f generates the magnetic field H f , and the current of the subsequent
strokes I s generates the magnetic field H s .
The magnetic induction effects are mainly determined by the rise of the magnetic field to the
maximum value. As shown in Figure A.2 the rise period of H f can be characterised by a damped
oscillating field of 25 kHz with the maximum value H f/max and the time to the maximum value T p/f of
10 µs. In the same way the rise period of H s can be characterised by a damped oscillating field of 1
MHz with the maximum value H s/max and the time to the maximum value T p/s of 0,25 µs.
From this follows, that with respect to the magnetic induction effects, the magnetic field of the first
stroke can be characterised by a typical frequency of 25 kHz and the magnetic field of the
subsequent strokes can be characterised by a typical frequency of 1 MHz. Damped oscillating
magnetic fields of these frequencies are defined for test purposes in IEC 61000-4-9 and IEC 610004-10.
By installing magnetic shields and SPD at the interfaces of the LPZ, the original lightning effect
defined by I 0 and H 0 is reduced to the immunity level of the victim. As shown in Figure A.1, the
victim shall withstand the surrounding magnetic field H 2 and the conducted lightning currents I 2 and
voltages U 2 .
The reduction of I 1 to I 2 and of U 1 to U 2 are subject of annex C, whereas the reduction of H 0 to a
sufficient low value of H 2 is considered here as follows:
In case of grid-like spatial shields, it can be assumed that the waveshape of the magnetic field
inside the LPZ (H 1 , H 2 ) is the same as the waveshape of the magnetic field outside (H 0 ).
In Figure A.2 it is shown that the tests defined in IEC 61000-4-9 and IEC 61000-4-10 simulate, in a
sufficient way, the rise of the magnetic field of the first stroke H f and of the subsequent strokes H s .
NOTE - If the buildings or room containing electronic system are sufficiently shielded against the magnetic field by large
volume shields, normally this measure will reduce the transient electric field to a sufficient low value.
A.2.2
Grid-like spatial shields
In practice, the large volume shields of LPZ are usually built by natural components of the structure
such as metal reinforcement in ceilings, walls and floors, metal frames, metal roofs and facades.
These components built up a grid-like spatial shield. An effective shielding requires typical mesh
widths below 5 m.
NOTE 1 – Therefore the shielding effect is negligible, if a LPZ 1 is created by a normal external LPS according to IEC
62305-3 with mesh widths and typical distances greater than 5 m. Otherwise a large steel frame building with
many structural steel stanchions provides a significant shielding effect.
62305-4 Ed. 1/CDV  IEC
– 37 –
NOTE 2 - Shielding in subsequent inner LPZs can be accomplished either by spatial room shielding measures, by closed
metal racks or cabinets or by metal housing of the apparatus.
Figure A.3 shows, in principle, how metal reinforcement in concrete and metal frames (for metal
doors and possibly shielded windows) can be built to a large volume shield for a building or a room.
Electronic systems shall be positioned only inside a safety volume respecting safety distances from
the shield of the LPZ (see Figure A.4). The reason are substantial high values of the magnetic field
close to the shield, because partial lightning currents could flow in the shield (especially LPZ 1).
A.2.3
Line routing and line shielding
Once spatial shielding of a LPZ is defined, the voltages or currents induced into the electronic
system can be further reduced by suitable line routing (thus minimising the induction loop area) or
by the use of shielded cables or cable ducts (thus minimising the induction effects inside).
Figure A.5 shows examples for spatial shielding, for line routing and shielding and for combining
both methods.
The lines and cables of electronic systems are to be led as close to the metal components of the
bonding network as possible. It is advantageous to embed the lines and cables into metal enclosures of the bonding network, for example U-shaped conduits or tubes (see also IEC 61000-5-2).
Close to the shield of LPZ (especially LPZ 1) particular attention shall be paid to the installation of
lines and cables due to the substantial value of the magnetic field.
If lines running between separate structures are to be protected, they should be laid inside metal
cable ducts, which shall be bonded at both ends to the bonding bars of the separate structures. If
the cable shields (bonded at both ends as said before) are able to carry the foreseeable partial
lightning current, additional metal cable ducts are not needed.
Voltages and currents induced into loops built up by installations result in conducted surges
(common mode) to the electronic system. For the calculation of these magnetically induced voltages
and currents see A.4.
Figure A.6 shows an example for a big office building:
•
Shielding is achieved by steel reinforcement and metal facades for LPZ 1 and by shielded
cabinets for highly sensitive electronic systems in LPZ 2. In order to be able to install a
narrow meshed bonding system, several bonding terminals are provided in every room.
•
LPZ 0 is extended into LPZ 1 to house a power supply of 20 kV, because the installation of
SPD on the high voltage power side immediately at the entrance was not possible in this
special case.
A.3
A.3.1
Magnetic field inside LPZ
Approximation for the magnetic field inside LPZ
If an individual theoretical (see A.3.2) or experimental (see A.3.3) investigation of the shielding
effectiveness is not done, the attenuation shall be evaluated as follows.
A.3.1.1
Grid-like spatial shield of LPZ 1 in case of direct lightning strikes
The shield of a building (shield surrounding LPZ 1) can be a part of an external LPS, and therefore
lightning currents will flow along it in case of a direct lightning strike. This situation is shown in
Figure A.7 assuming, that the lightning hits the structure at an arbitrary point of the roof.
62305-4 Ed. 1/CDV  IEC
– 38 –
For the magnetic field strength H 1 at an arbitrary point inside of LPZ 1 the following formula applies:
H 1 = k H · I 0 · w / (d w · d r )
(A/m)
where
d r (m)
d w (m)
I 0 (A)
kH 1 / m
(
)
w (m)
shortest distance between the point considered and the roof of shielded LPZ 1
shortest distance between the point considered to the wall of shielded LPZ 1
lightning current in LPZ 0 A
configuration factor. k H = 0,01 1 / m
(
)
mesh width of the grid-like shield of LPZ 1
From this follows for the maximum value of the magnetic field in LPZ 1 (considering NOTE)
•
caused by the first stroke:
H1/f/max = k H · I f/max · w / (dw ·√d r )
(A/m)
•
caused by the subsequent strokes:
H1/s/max = k H · I s/max · w / (dw ·√d r )
(A/m)
where
I f/max (A)
I s/max (A)
maximum value of the first stroke current according to the protection level
maximum value of the subsequent stroke currents according to the protection level
NOTE – The field is reduced by a factor of 2, if a meshed bonding network according to clause 5.2 is installed.
These magnetic field values are valid only for a safety volume V s inside the grid-like shield with a
safety distance d s/1 from the shield (see Figure A.4)
d s/1 = w (m)
Examples
As an example three typical grid-like shields may be defined, having the dimensions given in Table
A.1. For their grid-like shield of copper an average mesh width of w = 2 m is assumed. This results
in a safety distance d s/1 = 2,0 m defining the safety volume V s . The values for H 1/max valid inside V s
are calculated for i0/max = 100 kA and shown in Table A.1. The distance to the roof is half times the
height: d r = H/2. The distance to the wall is half times the length: d w = L/2 (centre) or equal to: d w =
d s/1 (worst case near the wall).
Table A.1 – Examples for i 0/max = 100 kA and w = 2 m
Type of shield
LxW xH
H 1/max (centre)
H 1/max (d w = d s/ 1 )
m
A/m
A/m
1
10 x 10 x 10
179
447
2
50 x 50 x 10
36
447
3
10 x 10 x 50
80
200
62305-4 Ed. 1/CDV  IEC
A.3.1.2
– 39 –
Grid-like spatial shield of LPZ 1 in case of nearby lightning strikes
The situation in case of a nearby lightning strike is shown in Figure A.8. The incident magnetic field
around the shielded volume of LPZ 1 can be approximated as a plane wave. The shielding factor SF
of grid-like spatial shields for a plane wave is given in Table A.2.
Table A.2 - Magnetic attenuation of grid-like spatial shields for a plane wave
Material
SF (dB) (see NOTE 1 and 2)
25 kHz (valid for the first stroke)
1 MHz (valid for subsequent strokes)
20 · log(8,5/w)
20 · log(8,5/w)
copper or
aluminium
steel (see NOTE 3)
20 • log
[ ( 8,5 / w ) / 1 + 18 • 10 / r ]
-6
w
mesh width of the grid-like shield (m)
r
radius of a rod of the grid-like shield (m)
2
20 · log(8,5/w)
NOTE 1 - SF=0 in case of negative results of the formulae
NOTE 2 - SF increases by 6 dB, if a meshed bonding network according to clause 5.2 is installed.
NOTE 3 - permeability µ r ≈ 200
The incident magnetic field H 0 shall be calculated as
H 0 = I 0 / (2 · π · s a ) (A/m)
where
I 0 (A) lightning current in LPZ 0 A
s a (m) distance between the point of strike and the centre of the shielded volume.
From this follows for the maximum value of the magnetic field in LPZ 0
•
caused by the first stroke:
H0/f/max
= If/max / (2 ·
· sa) (A/m)
•
caused by the subsequent strokes:
H0/s/max
= Is/max / (2 ·
· sa) (A/m)
where
I f/max (A)
I s/max (A)
maximum value of the lightning current of the first stroke according to the protection
level chosen
maximum value of the lightning current of the subsequent strokes according to the
protection level chosen.
The reduction of H 0 to H 1 inside LPZ 1 can be derived using the SF-values given in Table A.2:
H 1/max = H 0/max / 10
where
SF/20
(A/m)
62305-4 Ed. 1/CDV  IEC
SF (dB)
H 0/max (A/m)
– 40 –
shielding factor evaluated from the formulae of Table A.2
magnetic field in LPZ 0
From this follows for the maximum value of the magnetic field in LPZ 1
SF/20
(A/m)
SF/20
(A/m)
•
caused by the first stroke:
H 1/f/max = H 0/f/max / 10
•
caused by the subsequent strokes:
H 1/s/max = H 0/s/max / 10
These magnetic field values are valid only for a safety volume V s inside the grid-like shield with a
safety distance d s/2 from the shield (see Figure A.4)
d s/2 = w · SF / 10 (m)
for SF ≥ 10
d s/2 = w
for SF < 10
where
SF (dB)
w (m)
shielding factor evaluated from the formulae of Table A.2
mesh width of the grid-like shield.
For additional information about the calculation of the magnetic field strength inside grid-like shields
in case of nearby lightning strikes (see A.3.3).
Examples
The magnetic field strength H 1/max inside LPZ 1 in case of nearby lightning strikes depends on: the
lightning current I 0/max , the shielding factor SF of the shield of LPZ 1 and the distance s a between
the lightning channel and the centre of LPZ 1 (see Figure A.8).
The lightning current I 0/max depends on the LPL chosen (see IEC 62305-1). The shielding factor SF
(Table A.2) is mainly a function of the mesh width of the grid-like shield. The distance s a is either
•
a given distance between the centre of LPZ 1 and an object nearby (e.g. a mast) in case of
a lightning strike to this object, or
•
the minimum distance between the centre of LPZ 1 and the lightning channel in case of a
lightning strike to ground near to LPZ 1.
The worst case condition then is the highest current i 0/max combined with the closest distance s a
possible. As shown in Figure A.9, this minimum distance s a is a function of height H and length L
(respectively width W) of the structure (LPZ 1) and of the rolling sphere radius R corresponding to
I 0/max (Table A.3), defined from the electro-geometric model (see IEC 62305-1). The distance can be
calculated as
s a = 2 RH − H 2 + L / 2
for H < R
sa = R + L / 2
for H ≥ R
NOTE – For distances smaller than this minimum value the lightning strikes directly the structure.
Three typical shields may be defined, having the dimensions given in Table A.4. For their grid-like
shield of copper an average mesh width of w = 2 m is assumed. This results in a shielding factor SF
62305-4 Ed. 1/CDV  IEC
– 41 –
= 12,6 dB and in a safety distance d s/2 = 2,5 m defining the safety volume V s . The values for H 0/max
and H 1/max assumed to be valid everywhere inside Vs are calculated for I 0/max = 100 kA and shown in
Table A.4.
Table A.3 – Rolling sphere radius corresponding to maximum lightning current
Protection level
Maximum lightning current I 0/max
Rolling sphere radius R
kA
m
I
200
313
II
150
260
III - IV
100
200
Table A.4 – Examples for i 0/max = 100 kA and w = 2 m corresponding to SF = 12,6 dB
Type of shield
A.3.1.3
LxWxH
sa
H 0/max
H 1/max
m
m
A/m
A/m
1
10 x 10 x 10
67
236
56
2
50 x 50 x 10
87
182
43
3
10 x 10 x 50
137
116
27
Grid-like spatial shields of LPZ 2 and higher
In the grid-like shields of LPZ 2 and higher no essential partial lightning currents will flow. Therefore
in a first approach the reduction of H n to H n+1 inside LPZ n+1 can be evaluated as in clause A 3.1.2
for nearby lightning strikes:
H n+1
= H n / 10
SF/20
(A/m)
where
SF (dB)
H n (A/m)
shielding factor from Table A.2
magnetic field inside LPZ n (A/m).
NOTE – Evaluation of H n = H 1 : In case of lightning strikes direct to the grid-like shield of LPZ 1 see A 3.1.1 and Figure
A.7, in case of lightning strikes nearby to LPZ 1 see A 3.1.2 and Figure A.8, .
These magnetic field values are valid only for a safety volume V s inside the grid-like shield with a
safety distance d s/2 from the shield (as defined in A 3.1.2 and shown in Figure A.4).
A.3.2
Theoretical evaluation of the magnetic field due to direct lightning strikes
In A.3.1.1, the formulae for the assessment of the magnetic field strength H 1/max are based on
numerical magnetic field calculations for three typical grid-like shields shown in Figure A.9. For
these calculations a lightning strike to one of the edges of the roof was assumed. The lightning
channel was simulated by a vertical conducting rod of a length of 100m above the roof. The ground
was simulated by an ideally conducting plate.
For the calculation the magnetic field coupling of every rod of the grid-like shield with all other rods
including the simulated lightning channel was regarded, resulting in an equation system for the
calculation of the lightning current distribution in the grid. From this current distribution the magnetic
field strength inside the shield was derived. It was assumed that the resistance of the rods can be
neglected. Therefore the current distribution in the grid-like shield and the magnetic field strength
are independent from the frequency. Also capacitive coupling was neglected, so that transient
effects did not appear.
62305-4 Ed. 1/CDV  IEC
– 42 –
For the grid-like shield type 1 shown in Figure A.10, some results are presented in Figures A.11
and A.12. In all cases a maximum lightning current i o/max = 100 kA was assumed. In both figures
H 1/max is the maximum magnetic field strength in a point, derived from its components H x, H y and H z
H 1 / max = H x2 + H y2 + H z2
In Figure A.11 H 1/max is calculated along a straight line starting from the point of strike (x=y=0,
z=10m) and ending in the centre point of the volume (x=y=5m, z=5m). H 1/max is plotted as a function
of the x-co-ordinate of a point on this line. Parameter is the mesh width w of the grid-like shield.
In Figure A.12 H 1/max is calculated for two points inside the shield (point A: x=y=5m, z=5m; point B:
x=y=3m, z=7m). The result is plotted as a function of the mesh width w.
Both figures show the influence of the main parameters governing the magnetic field distribution
inside a grid-like shield: the distance from the wall or the roof and the mesh width. In Figure A.11 it
should be observed that along other lines through the volume of the shield there may be zero-axis
crossings and sign changes of the components of the magnetic field strength H 1/max . The formulae
in A.3.1.1 are therefore first order approximations of the real more complicated magnetic field
distribution inside a grid-like shield.
A.3.3
Experimental evaluation of the magnetic field due to direct lightning strikes
Besides the theoretical evaluations of the magnetic fields inside shielded structures, measurements
could be performed. Figure A.13 shows a proposal of the simulation of a direct lightning strike to an
arbitrary point of a shielded structure by the use of a lightning current generator. Normally, such
tests can be done as low level tests where the waveshape of the simulated lightning current shall be
identical to the original lightning current.
A.4
Calculation of induced voltages and currents
Only rectangular loops according to Figure A.14 are considered. Loops with other shapes should
be transformed into the rectangular configuration with the same loop area.
A.4.1
Situation inside LPZ 1 in case of direct lightning strikes
For the magnetic field H 1 inside volume V s of LPZ 1 applies (see A.3.1.1):
H 1 = k H · I 0 · w / (d w · d r )
(A/m)
For the open circuit voltage u oc applies
u oc = µo · b · ln(1 + l/d l/w ) · k H · ( w / d l/r )· dI 0 / dt (V)
During the front time T 1 the maximum value U oc/max arises
U oc/max = µo · b · ln(1 + l/d l/w ) · k H · ( w/ d l/r )· I 0/max /T 1 (V)
where
62305-4 Ed. 1/CDV  IEC
– 43 –
-7
µo
b (m)
d l/w (m)
d l/r (m)
I 0 (A)
I 0/max (A)
kH 1 / m
l (m)
T 1 (s)
w (m)
(
)
is equal to 4π · 10 (V·s)/(A·m)
width of the loop
distance of the loop from the wall of the shield, where d l/w ≥ d s/1
average distance of the loop from the roof of the shield
lightning current in LPZ 0 A
maximum value of the lightning current stroke in LPZ 0 A
configuration factor. k H = 0,01 1 / m
length of the loop
front time of the lightning current stroke in LPZ 0 A
mesh width of the grid-like shield
(
)
For the short circuit current I sc applies, if the ohmic resistance of the wires is neglected (worst
case), applies
I sc = µo · b · ln(1 + l/d l/w ) · k H · (w/ d l/r )· I 0 / L (A)
The maximum value I sc/max is given by
I sc/max
= µo · b · ln(1 + l/d l/w ) · k H · (w/ d l/r )· I o/max / L (A)
where
L (H)
self inductance of the loop.
For rectangular loops the self inductance L can be calculated from

L = {0,8 l 2 + b2 - 0,8 ( l + b ) + 0,4 • l • ln (2 b/ r ) /  1 +



+ 0,4 • b • ln  ( 2 l/ r ) /  1 +



1 + ( l / b )2  } • 10 - 6


1 + ( b / l )2 

(H)
where
r (m)
radius of the loop wire
For the voltage and current induced by the magnetic field of the first stroke (T 1 = 10 µs) applies
U oc/f/max = 1,26 · b · ln(1 + l/d l/w ) · (w/ d l /r )· I f/max (V)
-6
I sc/f/max = 12,6· 10 · b· ln(1 + l/dl/w )· (w/ d l / r )· I f/max /L (A)
For the voltage and current induced by the magnetic field of the subsequent strokes (T 1 = 0,25 µs)
applies
U oc/s/max = 50,4 · b · ln(1 + l/d l/w ) · (w/ d l / r )· I s/max (V)
-6
I sc/s/max = 12,6· 10 · b· ln(1 + l/d l/w )· (w/ d l / r )· I s/max/L (A)
where
I f/max (kA)
maximum value of the current of the first stroke
I s/max (kA)
maximum value of the current of the subsequent strokes
A.4.2
Situation inside LPZ 1 in case of nearby lightning strikes
The magnetic field H 1 inside volume V s of LPZ 1 is assumed to be homogeneous (see A.3.1.2).
62305-4 Ed. 1/CDV  IEC
– 44 –
For the open circuit voltage U oc applies
U oc = µo · b · l · dH 1 / dt (V)
During the front time T 1 the maximum value u oc/max , arises
U oc/max = µo · b · l · H 1/max / T 1 (V)
where
µo
-7
b (m)
H 1 (A/m)
H 1/max (A/m)
l (m)
T 1 (s)
is equal to 4 π · 10 (V·s)/(A·m)
width of the loop
time dependent magnetic field inside LPZ 1
maximum value of the magnetic field inside LPZ 1
length of the loop
front time of the magnetic field, identical with the front time of the lightning current
stroke
For the short circuit current I sc applies, if the ohmic resistance of the wires is neglected (worst
case), applies
I sc = µo · b · l · H 1 / L (A)
The maximum value I sc/max, is given by
I sc/max = µo · b · l · H 1/max / L (A)
where
L (H)
self inductance of the loop (for the calculation of L see c A.4.1).
For the voltage and current induced by the magnetic field H 1/f of the first stroke (T 1 = 10 µs) applies
U oc/f/max = 0,126 · b · l · H 1/f/max (V)
I sc/f/max = 1,26 · 10
-6
· b · l · H 1/f/max / L (A)
For the voltage and current induced by the magnetic field H 1/s of the subsequent strokes (T 1 = 0,25
µs) applies
U oc/s/max = 5,04 · b · l · H 1/s/max
I sc/s/max = 1,26 · 10
-6
(V)
· b · l · H 1/s/max/L
(A)
where
H 1/f/max (A/m) maximum of the magnetic field inside LPZ 1 due to the first stroke
H 1/s/max (A/m) maximum of the magnetic field inside LPZ 1 due to the subsequent strokes.
62305-4 Ed. 1/CDV  IEC
A.4.3
– 45 –
Situation inside LPZ 2 and higher
The magnetic field H n inside LPZ n for n ≥ 2 is assumed to be homogeneous (see A.3.1.3).
Therefore the same formulae for the calculation of induced voltages and currents apply as given in
A.3.1.2, where H 1 is to be substituted by H n .
62305-4 Ed. 1/CDV  IEC
– 46 –
I 0 , H 0 (LEMP)
Shield LPZ 1
LPZ 0
LPZ 1
Shield LPZ 2
H1
H2
LPZ 2
Apparatus
H0
SPD
SPD 1/2
SPD 0/1
(victim)
Shield (Housing)
U2 , I2
U1 , I1
U0 , I0
Partial
lightning
current
1. Primary source of harm is LEMP
defined from parameters according to LPL I to IV:
IEC 62305-1
I0
H0
impulse 10/350 µs (and 0,25/100 µs)
impulse 10/350 µs (and 0,25/100 µs)
200-150-100-100 kA
derived from I 0
2. Immunity of power installation
defined from installation category I to IV:
IEC 60664-1
U
Installation category I to IV
6-4-2,5-1,5 kV
3. Immunity of apparatus (victim)
defined from its immunity against conducted (U,I) and radiated (H) lightning effects:
IEC 61000-4-5
IEC 61000-4-9
U OC
I SC
H
IEC 61000-4-10
H
impulse 1,2/50 µ s
impulse 8/20 µs
impulse 8/20 µ s,
(damped oscillation 25kHz),T P = 10 µs
(impulse 0,2/0,5 µs),
damped oscillation 1MHz,T P = 0,25 µs
4-2-1-0,5 kV
2-1-0,5-0,25 kA
1000-300-100 A/m
100-30-10 A/m
Figure A.1 – LEMP situation due to lightning strike
62305-4 Ed. 1/CDV  IEC
– 47 –
Basic standard: IEC 61000-4-9
Figure A.2a - Simulation of the rise of the field of the first stroke (10/350 µs)
by a single impulse 8/20 µs (damped 25kHz oscillation)
Basic standard: IEC 61000-4-10
Figure A.2b - Simulation of the rise of the field of the subsequent stroke (0,25/100 µs)
by damped 1MHz oscillations (multiple impulses 0,2/0,5 µs)
NOTE 1 – Although the definitions of the time to the maximum value T P and the front time T 1 are different, for a suitable
approach their numerical values are taken as equal here.
NOTE 2 – The relation of the maximum values is H f /max / H s/max = 4 : 1
Figure A.2 – Simulation of the rise of magnetic field by damped oscillations
62305-4 Ed. 1/CDV  IEC
– 48 –
• welded or clamped at every rod and at the crossings
NOTE – In practice, it is not possible for extended structures to be welded or clamped at every point. However, most of
the points are naturally connected by direct contacts or by additional wiring. A practical approach therefore could
be a connection at about every 1 m.
Figure A.3 – Large volume shield built by metal reinforcement and metal frames
62305-4 Ed. 1/CDV  IEC
– 49 –
shield
Volume V s for
electronic
system
Cross-section A - A
Shield
NOTE – The volume V s shall keep a safety distance d s/1 or d s/ 2 from the shield of LPZ n.
Figure A.4 – Volume for electrical and electronic systems inside an inner LPZ n
62305-4 Ed. 1/CDV  IEC
– 50 –
1
Equipment
2
Line a (e.g. power line)
3
Line b (e.g. signal line)
4
Induction loop area
Figure A.5a - Unprotected system
1
Equipment
2
Line a (e.g. power line)
3
Line b (e.g. signal line)
4
Spatial shield
Figure A.5b - Reducing the magnetic field inside of an inner LPZ by its spatial shield
1
Equipment
2
Line a (e.g. power line)
3
Line b (e.g. signal line)
4
Line shielding
Figure A.5c - Reducing the influence of field on lines by line shielding
1
Equipment
2
Line a (e.g. power line)
3
Line b (e.g. signal line)
4
Minimised loop area
Figure A.5d - Reducing the induction loop area by suitable line routing
Figure A.5 - Reducing induction effects by line routing and shielding measures
62305-4 Ed. 1/CDV  IEC
– 51 –
Metal component on the roof
Equipment
on the roof
Interception mesh
Shielded
cabinet
Camera
Bonding
terminals
Metal facade
Steel reinforcement
in concrete
Ground level
Sensitive
electronic
equipment
Steel reinforcement
Extraneous metal services
Telecom lines
Extended
LPZ 0
Car parking
0,4 kV power line
20 kV power line
Metal cable conduit
(extended LPZ 0)
Foundation earthing electrode
•
equipotential bonding
±
surge protective device (SPD)
Figure A.6 – Example of an LPM for an office building
62305-4 Ed. 1/CDV  IEC
– 52 –
Roof
Wall
Ground level
Inside LPZ 1
H 1 = k H · i 0 · w 1 / (d w d·r
Inside LPZ 2
H 2 = H 1 / 10
)
SF2/20
Figure A.7 – Evaluation of the magnetic field values in case of a direct lightning strike
62305-4 Ed. 1/CDV  IEC
– 53 –
I0
No shield
H o = i o / (2 · π · s a )
Inside LPZ 1
H 1 = H 0 / 10
SF1/20
Inside LPZ 2
H 2 = H 1 / 10
SF2/20
Figure A.8 – Evaluation of the magnetic field values in case of a nearby lightning strike
62305-4 Ed. 1/CDV  IEC
– 54 –
I0/max
Figure A.9 – Distance s a depending on rolling sphere radius and structure dimensions
62305-4 Ed. 1/CDV  IEC
– 55 –
mesh width
Type 1
10m x 10m x 10m
Type 2
50m x 50m x 10m
Type 3
10m x 10m x 50m
Figure A.10 – Types of grid-like large volume shields
I 0/max = 100 kA
Figure A.11 – Magnetic field strength H 1/max inside a grid-like shield type 1
62305-4 Ed. 1/CDV  IEC
– 56 –
I 0/max = 100 kA
Figure A.12 – Magnetic field strength H 1/max inside a grid-like shield type 1
62305-4 Ed. 1/CDV  IEC
– 57 –
Multiple
feeder
Simulation of the close part
of the lightning channel
(in the range of 10 m)
Lightning
current
generator
Magnetic
field probe
Shield of
structure
Earth electrode
multiple connected
with the shield
Figure A.13a – Test arrangement
U: typical some 10 kV
C: typical some 10 nF
Figure A.13b – Lightning current generator
Figure A.13 – Low-level test to evaluate the magnetic field inside a shielded structure
62305-4 Ed. 1/CDV  IEC
– 58 –
Figure A.14 – Voltages and currents induced into a loop built by lines
62305-4 Ed. 1/CDV  IEC
– 59 –
Annex B
(informative)
Implementation of LEMP protection measures in existing structures
B.1
Checklist
In existing structures suitable protection measures against lightning effects need to take into
account the given construction and conditions of the structure and the existing electrical and
electronic systems.
A checklist facilitates risk analysis and selection of the most suitable protection measures.
For existing structures in particular, a systematic layout is to be set up for the zoning concept and
for earthing, bonding, line routing and shielding.
The checklist given in Tables B.1 to B.4 should be used to collect the required data of the existing
structure and its installations. Based on these data a risk assessment according to IEC 62305-2
shall be performed to determine the need of protection and, if so, to identify the most cost-effective
protection measures.
NOTE – For further information see IEC 60364-4-444
B.2
Integration of new electronic systems into existing structures
When adding new electronic systems to an existing installation, the existing installation might
restrict the protection measures that can be employed.
Figure B.1 shows an example where an existing installation, shown on the left, is interconnected to
a new installation, shown on the right. The existing installation has restrictions on the protection
measures that can be employed. However design and planning of the new installation can allow for
all necessary protection measures to be employed.
B.2.1
Overview of possible protection measures
Power supply
Existing mains supply (Figure B.1 no 1) in the structure is very often of the type TN-C, which can
cause power frequency interference. Such interference can be avoided by isolating interfaces (see
below).
If a new mains supply (Figure B.1 no 2) is installed, type TN-S is strongly recommended.
Surge protective devices
To control lightning created conducted surges on lines, SPD shall be installed at the entry into any
LPZ and possibly at the equipment to be protected (Figure B.1 no 3 and Figure B.2).
Isolating interfaces
To avoid interferences, isolating interfaces between existing and new equipment can be used: Class
II isolated equipment (Figure B.1 no 5), isolation transformers (Figure B.1 no 6), fibre optic cables
or optical couplers (Figure B.1 no 7).
Line routing and shielding
Large loops in line routing might lead to very high induced voltages or currents. They could be
avoided by adjacent routing of electrical and signal lines (Figure B.1 no 8) minimising the loop
area.
62305-4 Ed. 1/CDV  IEC
– 60 –
It is recommended to use shielded signal lines where permissible. Especially for extended
structures additional shielding for example by bonded metal cable ducts (Figure B.1 no 9) is also
recommended. All these shields shall be bonded at both ends.
Line routing and shielding measures become the more important, the smaller the shielding
effectiveness of the spatial shield of LPZ 1 and the larger the loop area is.
Spatial shielding
Spatial shielding of LPZ against lightning magnetic field requires typical mesh widths below 5m.
A LPZ 1 created by a normal external LPS according to IEC 62305-3 (Air-termination, downconductor and earth termination system) has mesh widths and typical distances greater than 5 m.
Therefore its shielding effect is negligible. If higher shielding effectiveness is required, the external
LPS shall be upgraded (see clause B.7).
LPZ 2 and higher usually requires spatial shielding to be able to protect sensitive electronic
systems.
Bonding
Equipotential bonding for lightning currents with frequencies up to several MHz requires a meshed
low impedance bonding network with typical mesh width of 5 m. All services entering a LPZ should
be bonded directly or by suitable SPD as close as possible at the boundary of LPZ.
If in existing structures these conditions cannot be fulfilled, other suitable protective measures
should be provided.
B.2.2
Establishment of LPZ for electrical and electronic systems
Depending on number, type and sensitivity of the electrical and electronic system, suitable inner
LPZ are defined, from small local zones (down to the housing of a single electronic equipment) up
to large integral zones (finally extended to the whole building volume).
Figure B.2 shows the principles of typical LPZ layout for protection of electronic systems providing
different solutions suitable especially for existing structures:
Figure B.2a shows the installation of a single LPZ 1, creating a protected volume inside the whole
structure, for quite robust electronic systems.
•
This LPZ 1 could be created by an LPS according to IEC 62305-3 consisting of an external
LPS (Air-termination, down-conductor and earth termination system) and an internal LPS
(Lightning equipotential bonding, compliance of the safety distance).
•
The external LPS protects LPZ 1 against direct lightning strikes, but the magnetic field
inside LPZ 1 remains nearly unattenuated (air terminations and down-conductors have mesh
widths and typical distances greater than 5 m, therefore the spatial shielding effect is
negligible as explained above). If the risk of direct lightning strikes is very low, the external
LPS can be omitted.
•
The internal LPS requires bonding of all services entering the structure at the boundary of
LPZ 1, which includes the installation of adequate SPD for all electrical and signal lines. By
this measure the lightning created conducted surges on the incoming services are
controlled.
•
If significant attenuation of the original lightning magnetic field inside LPZ 1 is required, this
can be achieved by integrating the natural metal components of the structure into the
external LPS creating a grid-like spatial shield of LPZ 1 (see B.7). Its shielding effectiveness
can be calculated according to A.4 and A.5.
62305-4 Ed. 1/CDV  IEC
•
– 61 –
Isolating interfaces could be useful inside LPZ 1 in order to avoid low-frequency
interference.
Figure B.2b shows the installation of an integral large volume LPZ 2 inside LPZ 1 for quite
sensitive electronic systems. The grid-like spatial shield of LPZ 2 provides a significant attenuation
of the lightning magnetic field. Here the SPD for all electrical and signal lines, coming from LPZ 0
and entering LPZ 2 immediately, are to be fitted at the transition from LPZ 0 via LPZ 1 to LPZ 2
according to annex C.
Figure B.2c shows the installation of individual LPZ 2 inside LPZ 1. Here additional SPD for the
electrical and signal lines at the boundary of each LPZ 2 are to be installed. These SPDs should be
co-ordinated with the SPD at the boundary of LPZ 1 according to annex C.
Figure B.2d shows the installation of several LPZ 2 with quite large volumes for all sensitive
electronic systems. The individual LPZ 2 are interconnected by shielded cable ducts creating one
continuous LPZ 2. Therefore only one set of SPD for the electrical and signal lines, coming from
LPZ 0 and entering LPZ 2 via a cable duct, is necessary, corresponding to the situation in Figure
B.2b.
B.3
Upgrading of power supply and cable installation inside the structure
Existing mains supply in old structures (Figure B.1 no 1) are very often of the type TN-C. Possible
50/60 Hz interference due to the connection of earthed signal lines with PEN conductors can be
avoided by the following measures:
•
Isolating interfaces using Class II electrical equipment or double insulated transformers.
This can be a solution, if there are only few electronic equipment (see B.5)
•
Installation of a new power supply of type TN-S (Figure B.1 no 2). This is the recommended
solution, especially for a large number of electronic equipment.
The requirements of earthing, bonding and line routing should be fulfilled.
B.4
Protection by surge protective devices
To control lightning created conducted surges on electrical lines, SPD according to annex C should
be installed at the entry into any inner LPZ (Figure B.1 no 3 and Figure B.2).
Within the building, an uncoordinated application of SPD can lead to malfunction or damage of the
electronic system, especially when local SPD or SPD within the equipment prevent the proper
function of the SPD at the entrance of the building.
In order to maintain the quality of the protection measures, it should be necessary to document the
location of all installed SPD.
B.5
Protection by isolating interfaces
Power frequency interference currents through the equipment and its connected signal lines can be
caused either by large loops or by the lack of a sufficiently low impedance bonding network. To
prevent such interference (mainly in TN-C installations), the suitable separation between existing
and new installations can be achieved using isolating interfaces, such as
•
Class II isolated equipment (i.e. double isolation without PE-conductor)
62305-4 Ed. 1/CDV  IEC
•
isolation transformer
•
metal-free fibre optic cables
•
optical couplers.
– 62 –
For the isolating interfaces used against lightning induced overvoltages enhanced withstand voltage
is required. A withstand voltage of about 5 kV for a waveshape 1,2/50 can be expected. Protection
of such interfaces against higher overvoltages - if needed - has to be performed by SPD, which
operate just below the withstand voltage. Otherwise SPD with much lower operating or limiting
voltages could violate safety requirements.
NOTE - Care should be taken that metal equipment enclosures do not have accidental galvanic connection to the bonding
network or to other metal parts. They shall be isolated from them. This is given in most of the situations, since
electronic equipment installed in domestic rooms or offices is linked to the earth references through their
connection cables only.
B.6
Protection measures by line routing and shielding
Suitable line routing and shielding are effective measures to reduce overvoltages. These measures
are especially important, if the spatial shielding effectiveness of LPZ 1 is negligible. In this case, the
following principles provide high protection against the effects of LEMP:
•
Minimising of induction loop area
•
Powering new equipment from the existing mains should be avoided, because it creates a
large enclosed induction loop area, which will increase significantly the risk of isolation
damage. Further large loops can be avoided by adjacent routing of electrical and signal lines
(Figure B.1 no 8).
•
Use of shielded cables or metal cable ducts
•
It is recommended to use shielded signal lines bonding the shield at least at both ends.
Additional shielding is possible by bonded metal plates or metal cable ducts with well
interconnected sections. The connections have to be performed by bolting of overlapping
parts or by the use of bonding conductors. In order to keep the impedance of the cable duct
low, multiple screws or strips have to be distributed over the perimeter of the cable duct
(see IEC 61000-5-2).
Examples of good line routing and shielding techniques are given in figures B.3 and B.4.
For signal connections of more than 10 m between electronic equipment within general areas, that
are not specifically designated for electronic systems, it is recommended to use balanced signal
lines with suitable galvanic isolation ports, e.g. by the use of optical couplers, signal isolation
transformers or isolation amplifiers. The additional use of triaxial cables can be advantageous.
B.7
Upgrading of an existing LPS for spatial shielding of LPZ 1
An existing LPS according to IEC 62305-3 around LPZ 1 can be upgraded by:
•
integrating existing metal facades and roof into the external LPS;
•
using the reinforcing bars from the topmost reinforced concrete roof down through the walls
to the earth termination of the structure, provided that electrical continuity can be assured;
62305-4 Ed. 1/CDV  IEC
– 63 –
•
reducing the spacing of the down conductors and reducing the mesh size of the air
termination system typically below 5 m;
•
installation of flexible bonding conductors across the expansion joints between adjacent but
structurally separated reinforced blocks.
B.8
Protection by a bonding network
Existing power frequency earthing systems might not give satisfactory equipotentialisation for
lightning currents with frequencies up to several MHz, because their impedance is too high at those
frequencies.
Even an LPS according to IEC 62305-3, which includes lightning equipotential bonding as
mandatory part of the internal LPS, might not be sufficient for sensitive electronic systems: The
bonding system with mesh widths and typical distances greater than 5 m might have too high
impedance.
A low impedance bonding network with typical mesh width of 5 m and below is strongly
recommended.
In general the bonding network should not be used either as a power return path or as a signal
return path. Therefore the PE conductor should be integrated into the bonding network, the PEN
conductor should not.
Direct bonding of a functional earthing conductor to a low impedance bonding network is allowed,
because in this case the interference coupling into electrical or signal lines will be very low. No
direct bonding is allowed to the PEN-conductor or to other metal parts connected to it, in order to
avoid power frequency interference in the electronic system.
B.9
Protection measures for externally mounted equipment
Examples for externally mounted equipment are sensors of any kind including aerials,
meteorological sensors, surveillance TV cameras, exposed sensors on process plants (pressure,
temperature, flow rate, valve position, etc.) and any other electrical, electronic or radio equipment
on external positions on structures, masts and process vessels.
B.9.1
Protection of the external equipment
Wherever possible, the equipment should be brought into LPZ O B using for example a local air
terminal to protected it against direct lightning strike (see Figure B.5). On tall structures, the rolling
sphere method (see IEC 62305-3) should be applied to equipment on top and sides of the building
to determine whether a direct strike is possible, and air terminations should be placed accordingly.
In many cases hand rails, ladders, pipes etc. can well perform the function of an air termination. All
equipment except some forms of aerials, can be protected in this manner. Aerials sometimes have
to be placed in exposed positions because their performance is adversely affected by lightning
conductors nearby. Some aerial designs are inherently self-protecting because only well earthed
conductive elements are exposed to lightning strike. Other types, not so well protected, might need
SPD on their feed cables to prevent excessive transients from flowing down the cable to the
receiver or the transmitter. However when an external LPS is available, the support of aerials
should be bonded to it.
B.9.2
Reduction of overvoltages in cables
High induced voltages and currents can be prevented using bonded ducting, trunks or metal tubes.
All cables leading to the specific equipment should leave the cable duct at a single point. Maximum
advantage should be taken of the inherent shielding properties of the structure itself by running
cables within tubular components if possible. Where this is not possible, as in the case of process
62305-4 Ed. 1/CDV  IEC
– 64 –
vessels, cables should run on the outside but close to the structure and making most use of natural
shielding provided by metal pipes, steel rung ladders and any other well bonded conducting
material (Figure B.6). On masts which use L-shaped corner members (Figure B.7) cables should
be placed in the inside corner of the L for maximum protection.
B.10 Upgrading of interconnections between structures
Lines interconnecting separate structures are either
•
isolating (metal free fibre optic cables) or
•
metallic (e.g. wire pairs, wave guides, coaxial cables, multicores, but also fibre optic cables
with continuous metal components).
Protection requirements depend on the type of the line, the number of lines, and whether the earth
termination systems of the structures are interconnected.
B.10.1
Isolating lines
If metal-free fibre optic cables (i.e. without metal armouring, moisture barrier foil or steel internal
draw wire) are used to interconnect separate structures, no protection measures for these cables
are needed.
B.10.2
•
•
Metallic lines
Without proper interconnection between the earth termination systems of separate
structures, the interconnecting lines form a low impedance route for the lightning current.
Therefore a substantial part of the lightning current will flow along the interconnecting lines.
•
The required bonding directly or by SPD at the entries to both LPZ 1 will protect only
the equipment inside, whereas the lines outside remain unprotected.
•
The lines might be protected installing an additional bonding conductor in parallel.
The lightning current then will be shared between them.
•
The recommended method is to place the lines in closed and interconnected metal
cable ducts. In this case the lines as well as the equipment can be protected.
With proper interconnection between the earth termination systems of separate structures,
the protection of lines by interconnected metal ducts is still recommended. In case of many
cables between interconnected structures, the shields or the armouring of cables, bonded at
each end, can be used instead of cable ducts.
Table B.1 - Structural characteristics and surroundings
Item
Questions
1
Masonry, bricks, wood, reinforced concrete, steel frame structures, metal facade ?
2
One single structure or interconnected blocks with expansion joints?
3
Flat and low or high-rise structures? (Dimensions of the structure)
4
Reinforcing rods electrically connected throughout the structure?
5
Kind, type and quality of metallic roof material ?
62305-4 Ed. 1/CDV  IEC
– 65 –
6
Metal facades bonded ?
7
Metal frames of the windows bonded ?
8
Size of the windows ?
9
Structure equipped with an external LPS ?
10
Type and quality of this LPS ?
11
Material of ground (rock, soil) ?
12
Height, distance and earthing of adjacent structures ?
NOTE - For detailed information see IEC 62305-2
Table B.2 - Installation characteristics
Item
Questions
1
Type of incoming services (underground or overhead) ?
2
Type of aerials (antennas or other external devices) ?
3
Type of power supply (High voltage, low voltage, overhead or underground)?
4
Line routing (number and location of risers, cable ducts) ?
5
Use of metal cable ducts ?
6
Are the electronics self contained within the structure ?
7
Metal conductors to other structures ?
NOTE - For detailed information see IEC 62305-2
Table B.3 - Equipment characteristics
Item
Questions
1
Type of electronic system links (shielded or unshielded multicore cables, coaxial cable, analog and/or
digital, balanced or unbalanced, fibre optic cables)? (see NOTE 1)
2
Immunity level of the electronic system specified? (see NOTE 1 and 2)
NOTE 1 - For detailed information see IEC 62305-2
NOTE 2 - For detailed information see ITU-T K.21, IEC 61000-4-5, IEC 61000-4-9 and IEC 61000-4-10
Table B.4 - Other questions to be considered for the protection concept
Item
Questions
1
Configuration TN (TN-S or TN-C), TT or IT ?
2
Location of the electronic equipment ? (see NOTE)
3
Interconnections of functional earthing conductors of the electronic system with the bonding network ?
NOTE-For detailed information see Annex A
62305-4 Ed. 1/CDV  IEC
New installations
Power
sub distribution
Existing installations
– 66 –
1
2
3
4
5
6
7
8
9
Existing mains (TN-C,TT,IT)
New mains (TN-S,TN-CS,TT,IT)
Surge protective device (SPD)
Class I standard isolation
Class II double isolation without PE
Isolation transformer
Opto-coupler or fibre optic cable
Adjacent routing of electrical and signal lines
Shielded cable ducts
E
S
ET
BN
PE
FE
•
Electrical lines
Signal lines (shielded or unshielded)
Earth termination system
Bonding network
Protective earthing conductor
Functional earthing conductor (if any)
3-wire electrical line: L, N, PE
2-wire electrical line: L, N
Bonding points (PE, FE, BN)
Figure B.1 – Upgrading of LEMP protection measures and electromagnetic compatibility in
existing structures
62305-4 Ed. 1/CDV  IEC
– 67 –
Figure B.2a – Unshielded LPZ 1 for robust new electronic systems
Spatial shield
Figure B.2b – Large LPZ 2 for sensitive new electronic systems
62305-4 Ed. 1/CDV  IEC
– 68 –
Spatial shield
Figure B.2c – Local LPZ 2 and small local LPZ 2 for sensitive new electronic systems
Spatial shield
Figure B.2d – Several interconnected local LPZ 2 for sensitive new electronic systems
Figure B.2 - Possibilities to establish LPZs in existing structures
62305-4 Ed. 1/CDV  IEC
1
2
3
4
– 69 –
PE, only when Class I equipment is used
Optional cable shield needs to be bonded at both ends
Metal plate as additional shield (see Figure B.4).
Small loop area
NOTE - Owing to the small loop area, the induced voltage between the cable shield and the metal plate is small.
Figure B.3 - Reduction of loop area using shielded cables close to a metal plate.
1
2
E
S
Cable fixing with or without bonding of cable shields to the plate
At edges, the magnetic field is higher than in the middle of the plate
Electrical lines
Signal lines
Figure B.4 - Example of a metal plate for additional shielding
62305-4 Ed. 1/CDV  IEC
1
2
3
4
5
6
R
– 70 –
Lightning rod
Steel mast with antennas
Hand rails
Interconnected reinforcement
Line coming from LPZ 0B needs SPD at entry
Lines coming from LPZ 1 (inside the mast) may not need SPDs at entry
Radius of the rolling sphere
Figure B.5 – Protection of aerials and other external equipment
62305-4 Ed. 1/CDV  IEC
– 71 –
1
2
3
Process vessel
Rung ladder
Pipes
NOTE – A, B, C are good alternatives for cable tray positioning
Figure B.6 - Inherent shielding provided by bonded ladders and pipes
1
2
Ideal positions for cables in corners of L-girders
Alternative position for bonded cable tray within the mast
Figure B.7 - Ideal positions for lines on a mast (cross-section of steel lattice mast)
62305-4 Ed. 1/CDV  IEC
– 72 –
Annex C
(informative)
SPD co-ordination
C.1
General
Where two or more SPD are installed subsequently in the same circuit, they shall be energy coordinated to share the stress among them according to their energy absorbing capability
For an effective co-ordination, the characteristics of the individual SPD (as published by the
manufacturer), the threat at their place of installation and the characteristics of the equipment to be
protected shall be considered.
The primary lightning threat is given by the three lightning current components:
•
first short stroke
•
subsequent short strokes
•
long stroke.
All three components are imposed currents. Concerning the co-ordination of subsequently installed
SPD, the first short stroke is the decisive factor, because the subsequent short strokes have lower
values for specific energy, charge and amplitude, but a higher current steepness. Moreover, the
long stroke is only an additional stress factor for SPD (Class I tested) and is therefore not
considered for co-ordination purposes.
NOTE - If SPD are specified for the first short stroke threat, the subsequent short strokes cause no additional problems. If
inductances are used as decoupling elements, the higher current steepness facilitates decoupling.
The parameters of the total lightning current for the different LPL are listed in IEC 62305-1, Table 3.
However, a single SPD will only be stressed with a portion of the total lightning current. This
requires the determination of the current distribution, either by computer simulation using network
analysing software or by approximation as given in IEC 62305-3 Annex B.
NOTE - Analytical functions of the short strokes for analysis purposes are given in IEC 62305-1, Annex B.
The first short stroke current of a direct lightning strike can be simulated with a waveshape 10/350.
But partial lightning or induced currents within the system can have different waveshapes due to
interaction between the lightning current and the low-voltage installation. For co-ordination
purposes therefore the following impulse test currents (surges) are considered:
I 10/350
A test current with a waveshape 10/350. It is used especially to test the energy co-ordination
of SPDs. A similar current is used for the Class I test for SPD (IEC 61643-1), defined there
by its peak value and its charge.
I 8/20
A test current with a waveshape 8/20. The same waveshape is used for Class II test (IEC
61643-1).
I CW G
Output current of a combination wave generator (IEC 61000-4-5). The waveshape depends
on the load (open circuit voltage 1,2/50 and short circuit current 8/20). It is used for the
Class III test (IEC 61643-1).
I RAMP
A test current with a current steepness of 0.1kA/µs. It is defined to simulate partial lightning
currents within the system having minimum steepness due to interaction between the
lightning current and the low-voltage installation. This current is used especially to test
decoupling of subsequent SPDs.
62305-4 Ed. 1/CDV  IEC
– 73 –
Figure C.1 shows an example for the application of SPD in power distribution systems according to
the lightning protection zones concept. The SPD are installed in sequence. They are chosen
according to the requirements at their particular penetration point.
The chosen SPD and their integration into the whole electrical system inside the structure shall
ensure, that the partial lightning current will mainly be discharged into the earthing system at the
interface LPZ 0 A to LPZ 1.
Once the initial energy of the partial lightning current has been mainly dissipated, the subsequent
SPD need to be designed only to cope with the remaining threat from the interface LPZ 0 A to LPZ 1
plus the induction effects from the electromagnetic field within LPZ 1 (especially if LPZ 1 has no
electromagnetic shield).
NOTE - If voltage switching type SPDs are installed, it shall also be considered for the stress of the subsequent SPD, that
the SPD before might not reach its operating threshold.
Lines incoming from LPZ 0 A (where direct strikes are possible), carry partial lightning currents. At
the interface LPZ 0 A to LPZ 1 therefore SPD (Class I tested) are needed to divert these currents.
Lines incoming from LPZ 0 B (where direct strikes are excluded, whereas full electromagnetic field
exist), carry only induced surges. In this case at the interface LPZ 0 B to LPZ 1 the induced effects
should be simulated by means of either a surge current with a waveshape 8/20 (Class II test) or an
adequate combination wave test (Class III test) according to IEC 61643-1.
The remaining threat of zone transition of LPZ 0 to LPZ 1 and the induced effects by the
electromagnetic field within LPZ 1 define the requirements for the SPD at the interface from LPZ 1
to LPZ 2. If no detailed analysis of the threat is possible, the dominant stress should be simulated
by means of either a surge current with a waveshape 8/20 (Class II test) or an adequate
combination wave test (Class III test) according to IEC 61643-1. If the preceding SPD is a switching
type device (especially at the interface LPZ 0 to LPZ 1), the waveshape 10/350 shall also be
considered, as long as this SPD is not triggered.
C.2
General objective of co-ordination
The energy co-ordination shall avoid, that SPD within a system are overstressed. The individual
stresses of SPD, depending on their location and characteristics, must therefore be determined.
As soon as two ore more SPD are installed subsequently, a co-ordination study for the SPDs and
the equipment to be protected is needed.
The energy co-ordination is achieved, if for all surge currents the portion of energy, dissipated by
any SPD, is lower than or equal to their withstand energy.
The withstand energy should be obtained from
•
electrical testing according to IEC 61643-1
•
technical information of the manufacturer of the SPD.
Figure C.2 illustrates the basic model of the energy co-ordination for SPD. This model is only valid,
when the impedance of the bonding network and the mutual inductance between the bonding
network and the installation formed by the connection of SPD 1 and SPD 2 is negligible.
NOTE – The decoupling element is not needed, if the energy co-ordination is assured by other suitable measures (e.g. coordination of the voltage/current characteristics or use of triggered SPD).
62305-4 Ed. 1/CDV  IEC
C.2.1
– 74 –
Co-ordination principles
The co-ordination between SPD uses one of the following principles:
•
Co-ordination of the voltage/current characteristics (without decoupling elements)
This method is based on the stationary voltage/current characteristic and is applicable to
voltage limiting type SPD (e.g. MOV or suppressor diodes). This method is not very sensitive to
current waveshape.
NOTE – This method does not need decoupling, even if some inherent decoupling is given from the natural
impedance of the lines.
•
Co-ordination using dedicated decoupling elements
For co-ordination purposes impedances with sufficient surge withstand capability can be used
as decoupling elements. Resistances are primarily used in information systems. Inductances
are primarily used for power systems. For the co-ordination efficiency of inductances the
current steepness dI/dt is the decisive parameter.
NOTE 1 - Decoupling elements can be realised either by separate devices, or by using the natural impedance of
cables between subsequent SPD.
NOTE 2 - The inductance of a line is that of two parallel conductors: If both conductors (phase and ground wire) are
within one cable, then the inductance is about 0.5 to 1 µH/m (depending on the cross-section of the
wires). If both conductors are separated, higher inductances should be assumed (depending on the
separation distance of both conductors).
•
Co-ordination using triggered SPD (without decoupling elements)
The co-ordination can also be achieved using triggered SPDs. Their electronic trigger circuit
has to assure, that the energy withstand capability of subsequent SPD is not exce ded.
NOTE – This method does not need decoupling, even if some inherent decoupling is given from the natural
impedance of the lines.
C.2.2
Co-ordination of two voltage limiting type SPD
Figure C.3a shows the basic circuit diagram for the co-ordination of two voltage limiting type SPD
(MOV). Figure C.3b illustrates the energy dispersion within the circuit. The total energy feed into
the system increases with the growing impulse current. As long as the energy dissipated in each of
the two MOV does not exceed its withstand energy, the energy co-ordination is achieved.
The energy co-ordination of voltage limiting type SPD without dedicated decoupling elements
should be realised by means of their stationary voltage/current characteristic for the relevant
current range. This method is not very sensitive to the current waveshape. If inductances are used
as decoupling elements, the waveshape of the surge current shall be considered (e.g. 10/350 or
8/20).
For waveshapes with a low current steepness (e.g. 0.1 kA/µs), inductances are not very effective
for decoupling voltage limiting type SPD. If possible, the co-ordination should be achieved using
resistances (or natural resistances of cables) as decoupling elements.
If two voltage limiting type SPD are co-ordinated, both shall be dimensioned for the respective
surge current and energy. The current wave duration will not be remarkably shortened compared to
the impinging current. Figures C.4a and C.4b give an example for the energy co-ordination
between two voltage limiting type SPD (MOV) in case of a 10/350 surge.
62305-4 Ed. 1/CDV  IEC
C.2.3
– 75 –
Co-ordination of voltage switching type and voltage limiting type SPD
Figure C.5a shows the basic circuit diagram of this co-ordination variant using a spark gap (SG)
and a MOV as example technologies. Figure C.5b illustrates the basic principle of energy coordination for the combination of a voltage switching type SPD 1 and a voltage limiting type SPD 2.
The ignition of the SG (SPD 1) depends on the sum of the residual voltage U 2 across the MOV
(SPD 2) and of the dynamic voltage drop across the decoupling element U DE . As soon as the
voltage U 1 exceeds the dynamic spark over voltage U SPARK , the SG will ignite and the co-ordination
is achieved. This depends only on the
•
characteristics of the MOV
•
steepness and magnitude of the incoming surge current
•
decoupling element (inductance or resistance) (see IEC 61643-1).
When an inductance is used as decoupling element, rise time and peak magnitude of the surge
current shall be considered (e.g. for waveshape 10/350 or 8/20). The greater the steepness dI/dt,
the smaller is the inductance required for decoupling. Especially for co-ordination between SPD
(Class I tested) and SPD (Class II tested) a lightning current with a minimum current steepness of
0,1 kA/µs has to be taken into account (see IEC 62305-1 Annex C.1). The co-ordination of those
SPD has to be ensured, both for the 10/350 lightning current as well as for the minimum current
steepness of 0,1 kA/µs.
Two basic situations are to be considered:
•
No ignition of the spark gap (Figure C.6a):
If the SG does not ignite, the complete surge current flows through the MOV. As shown in Figure
C.5b the co-ordination has not been achieved, if the energy dissipated by this surge is higher than
the withstand energy of the MOV. If an inductance is used as a decoupling element, the worst case
is the minimum current steepness of 0,1 kA/µs.
•
Ignition of the spark gap (Figure C.6b):
If the SG does ignite, the duration of the current flowing through the MOV is considerably reduced.
As shown in Figure C.5b the proper co-ordination is achieved when SG ignites before the withstand
energy of the MOV is reached.
Determination of the decoupling inductance
Figure C.7 shows the procedure for determination of the required decoupling inductance for both
criteria: the 10/350 lightning current as well as the 0.1kA/µs minimum lightning current steepness.
The dynamic voltage/current characteristics of both SPD shall be considered to determine the
decoupling element required. The condition for successful co-ordination is, that SG shall ignite,
before the withstand energy of the MOV is reached.
The ignition of the SG depends on its spark over voltage U SPARK and on the sum of the voltage U 2
across the MOV (SPD 2) and of the voltage across the decoupling element U DE . The voltage U 2
depends on the current i (see voltage/current characteristic of the MOV), whereas the voltage U DE =
L DE · dI/dt depends on the current steepness.
For the 10/350 surge, the current steepness dI/dt ≈ I ma x / 10 µs depends on the permissible
amplitude I max of the MOV (determined from its withstand energy W max). Because both voltages U DE
and U 2 are functions of I max, the voltage U 1 across the SG depends also on I max. The higher I max , the
higher is also the steepness of the voltage U 1 across the SG. For this criterion therefore, the spark
over voltage U SPARK of the SG is usually described by the “Impulse spark over voltage at 1 kV/µs“.
62305-4 Ed. 1/CDV  IEC
– 76 –
For the 0.1 kA/µs ramp, the current steepness dI/dt = 0.1 kA/µs is constant. Thus the voltage U DE is
constant too, whereas the voltage U 2 is a function of I max as before. The steepness of the voltage U 1
across the SG therefore follows the voltage/current characteristic of the MOV and is much lower
compared to the first case. Because of the dynamic operating voltage characteristic of the SG, its
spark over voltage decreases with a longer duration of the voltage drop across the SG (This
duration depends on I max derived from the withstand energy W max of the MOV). Hence, the spark
over voltage U SPARK should be assumed to decrease almost to the “DC-operating voltage at 500V/s“
for increasing duration of current flowing through the MOV.
The higher value of both inductances L DE-10/350 and L DE-0.1kA/µs finally shall be applied for the
decoupling inductance L DE . See Figures C.8 and C.9 for examples.
NOTE – For the determination of a decoupling element in a low-voltage power system, the worst case would be a short
circuit at SPD 2 (U 2 = 0), hence maximising the required voltage U DE . Where SPD 2 is a voltage limiting type it
has a residual voltage U 2 > 0, which will reduce considerably the required voltage U DE . This residual voltage is at
least higher than the peak voltage of the power supply (e.g. AC nominal voltage 230 V: peak value 2 · 230 V =
325 V). Taking into account this residual voltage of SPD 2 leads to suitably dimensioned decoupling elements.
Otherwise they would be over dimensioned.
C.2.4
Co-ordination of two voltage switching type SPD
This co-ordination variant is described using spark gaps (SG) as example technologies. For the coordination between spark gaps, the dynamic operating characteristics shall be used.
After ignition of SG 2, the co-ordination will be realised by means of a decoupling element. To
determine the required value of the decoupling element, SG 2 can be replaced by a short-circuit.
For the ignition of SG 1, the dynamic voltage drop across the decoupling element shall be higher
than the operating voltage of SG 1.
Using inductances as decoupling elements, the required U DE depends mainly on the steepness of
the surge current. Therefore waveshape and steepness of the surge shall be considered.
Using resistances as decoupling elements, the required U DE depends mainly on the peak value of
the surge current. This value shall be considered also, when selecting the pulse rating parameters
of the decoupling element.
After the ignition of the SG 1, the total energy will be subdivided according to the stationary
voltage/current characteristics of the individual elements.
NOTE - In the case of spark gaps or gas discharge tubes the impulse steepness is of major importance.
C.3
Basic co-ordination variants for protection systems
There are four co-ordination variants for protection systems: The first three use one-port SPDs,
whereas the fourth uses two-port SPD with integrated decoupling elements. These co-ordination
variants should be considered, where also internal SPD, which might be integrated in the equipment
to be protected, should be considered.
C.3.1
Variant I
All SPD have a continuous voltage/current characteristic (such as MOV or suppressor diodes) and
the same residual voltage U RES . The co-ordination of the SPDs and of the equipment to be
protected is normally achieved by the impedances of lines between them (Figure C.10).
C.3.2
Variant II
All SPD have a continuous voltage/current characteristic (such as MOV or suppressor diodes). The
residual voltage U RES rises stepwise from SPD 1 to SPD 3 (Figure C.11).
This is a co-ordination variant for power supply systems.
62305-4 Ed. 1/CDV  IEC
– 77 –
NOTE - This variant requires that the residual voltage of the protective component inside the equipment to be protected
(SPD 4) is higher than the residual voltage of the SPD installed directly before (SPD 3).
C.3.3
Variant III
SPD 1 has a discontinuous voltage/current characteristic (such as spark gaps). Subsequent SPD
have a continuous voltage/current characteristic (such as MOV or suppressor diodes). All SPDs
have the same residual voltage U RES (Figure C.12).
The characteristic of this variant is, that by the switching behaviour of SPD 1, a reduction of the
time to half value of the original current impulse 10/350 will be achieved, which relieves the
subsequent SPD considerably.
NOTE - Additional information concerning information lines is given in ITU-TS.
C.3.4
Variant IV
There are two-port SPD available, which incorporate cascaded stages of SPD internally coordinated with series impedances or filters (Figure C.13). The successful internal co-ordination
means minimum energy transfer to downstream SPD or equipment. These SPD shall be fully coordinated with other SPD in the system in accordance to variant I, II or III as appropriate.
NOTE – The series impedance or the filter can be omitted, if the energy co-ordination is assured by other suitable
measures (e.g. co-ordination of the voltage/current characteristics or use of triggered SPD).
C.4
Co-ordination according to the “let through energy” method
Impulses from a combination wave generator can be used to select and co-ordinate SPD. The main
advantage of this method is the possibility to consider an SPD like a black box (Figure C.14). For a
given surge at the input of SPD 1 the output values of open circuit voltage as well as of short-circuit
current are determined ("let through energy" method). These output characteristics are converted
into an equivalent “2 Ω combination wave stress” (open circuit voltage 1.2/50, short circuit current
8/20). The advantage is that there is no need of special knowledge of the internal design of the
SPD.
NOTE - This method gives good results when SPD 2 has no feedback to SPD 1. That means, that the surge conditions at
the input of SPD 2 are quasi imposed current conditions. This is given when the voltage/current characteristics of
SPD 1 and SPD 2 are much different (e.g. as for the co-ordination of a spark gap with a MOV).
The aim of this co-ordination method is to make the input values of SPD 2 (e. g. discharge current)
comparable to the output values of SPD 1 (e. g. voltage protection level).
For proper co-ordination the equivalent combination wave at the output of SPD 1 shall not exceed
the combination wave, which can be absorbed by SPD 2 without damage.
The equivalent combination wave at the output of SPD 1 shall be determined for the worst case of
the stress (I max, U max , let-through energy).
NOTE - Additional information concerning this co-ordination method is given in IEC 61643-12.
62305-4 Ed. 1/CDV  IEC
C.5
– 78 –
Proving co-ordination
The co-ordination should be proved by:
•
Co-ordination test
Co-ordination could be demonstrated on a case by case basis.
•
Calculation
Simple cases can be approximated, complex systems require computer simulation.
•
Application of co-ordinated SPD families
In this case, the manufacturer of the SPD shall prove the co-ordination.
•
Using the “let through energy” method.
62305-4 Ed. 1/CDV  IEC
– 79 –
LPZ 0 A
LPZ 0 B
LPZ 1
SPD II
LPZ 2
SPD III
Power
line
SPD II
SPD I
SPD II
LPZ 3
SPD III
Surge protective device (e.g. Class II tested)
Decoupling element or length of cable
Figure C.1 - Example for the application of SPD in power distribution systems
Protected side
Decoupling element
Surge
U DE , I DE
SPD1
SPD2
U1, I 1
U2, I 2
Figure C.2 - Basic model for energy co-ordination of SPD
62305-4 Ed. 1/CDV  IEC
– 80 –
Protected side
Decoupling element
Surge
U DE ,
MOV 1 SPD1
U1, I 1
U2, I 2
SPD2 MOV 2
Figure C.3a – Circuit with MOV 1 and MOV 2
W [kJ]
2.0
1.8
1.6
1.4
MOV 1
1.2
Total
1.0
0.8
W max (MOV 1)
0.6
MOV 2
0.4
W max (MOV 2)
0.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
I SURGE [kA]
Figure C.3b - Principle for energy co-ordination of MOV 1 and MOV 2
Figure C.3 - Combination of two voltage limiting type MOV 1 and MOV 2
62305-4 Ed. 1/CDV  IEC
– 81 –
U [V]
1.5•103
U/I-characteristic MOV 1
1.0•103
U/I-characteristic MOV 2
6.7•102
U REF (1mA)
4.5•102
MOV 1
Maximum surge current
3.0•102
MOV 2
Maximum surge current
2.0•102
10
-6
10
-3
10
10
3
10
5
I [A]
Note - As it can be seen in this example the knowledge of the MOV reference voltage U REF only, is not sufficient for coordination purposes
Figure C.4a - Current/voltage characteristics of MOV 1 and MOV 2
U[V]
I[kA]
1.0
800
0.9
700
I SURGE
0.8
0.7
600
I 1 (MOV 1)
500
0.6
0.5
300
0.3
200
i 2 (MOV 2)
0.2
0.1
0.0
0.0
U 1 (MOV 1)
400
I 2 (MOV 2)
0.4
U 2 (MOV 2)
100
0.2
0.4
0.6
0.8
1.0
t[ms]
0
0.0
0.2
0.4
0.6
0.8
1.0
t[ms]
Figure C.4b – Current and voltage at MOV1 and MOV 2 from 10/350 surge
Figure C.4 - Example with two voltage limiting type MOV 1 and MOV 2
62305-4 Ed. 1/CDV  IEC
– 82 –
Protected side
Decoupling element
Surge
U DE ,
SG SPD1
SPD2 MOV
U1, I 1
U2, I 2
Figure C.5a – Circuit with SG and MOV
W [kJ]
1.0
Maximum current SG
0.8
Co-ordination not achieved
0.6
MOV
Withstand energy W max of MOV
0.4
Co-ordination achieved
No ignition of SG
SG
0.2
Ignition of SG
MOV
0.0
1.0
2.0
3.0
4.0
5.0
I SURGE [kA]
Figure C.5b - Principle for energy co-ordination of SG and MOV
Figure C.5 – Combination of voltage switching type SG and voltage limiting type MOV
62305-4 Ed. 1/CDV  IEC
– 83 –
I [kA]
U [kV]
1,0
2,5
I SURGE
0,8
0,6
1,5
I 2 (MOV)
U 2 (MOV)
1,0
0,4
I 1 (SG)
0,2
0,0
U 1 (SG)
2,0
0,0
0,2
0,4
0,5
0,6
0,8
1,0
t [ms]
0,0
0,0
0,2
0,4
0,6
0,8
1,0
t [ms]
Figure C.6a – Current and voltage at SG and MOV from 10/350 surge (SPD 1 not ignited)
I [kA]
1,50
U [kV]
3,5
I SURGE
1,25
3,0
1,00
I 1 (SG)
0,75
0,50
1,0
0,25
0,00
U 1 (SG)
2,0
U 2 (MOV)
I 2 (MOV)
0
100
200
300
400
500
t [µs]
0,0
0
100
200
300
400
500
t [µs]
Figure C.6b – Current and voltage at SG and MOV from 10/350 surge (SPD 1 ignited)
Figure C.6 - Example with voltage switching type SG and voltage limiting type MOV
62305-4 Ed. 1/CDV  IEC
– 84 –
Decoupling element L DE = ?
Surge
Protected side
U DE , I DE
10/350
or
0,1 kA/µs
SG
SPD1
SPD2 MOV
U1, I 1
Voltage condition
Ignition of SG
Co-ordination achieved
U2, I 2
U 1 = U 2 + U DE = U 2 + L · dI/dt
U 1 = U SPARK
Ignition of SG before withstand energy W max of MOV is exceeded
Energy co-ordination with 10/350 surge
Energy co-ordination with 0.1kA/µs surge
U[V]
U[V]
U/I characteristic MOV
U/I characteristic MOV
U REF (1mA)
U REF (1mA)
I max =f(W max)
I max =f(W max)
10
-3
I1
I[A]
I2
10
(I 1 < I max for (L DE-1 ≥ L DE-10/350 )
(I 2 > I max for (L DE-2 ≤ L DE-10/350 )
-3
I1
I2
I[A]
(I 1 < I max for (L DE-1 ≥ L DE-0.1kA/µs )
(I 2 > I max for (L DE-2 ≤ L DE-0.1kA/µs )
I
I2
I1
time
U
t1
t2
t1
t2
U SPARK-1
U SPARK-2
L DE = (U SPARK – U 2 ) / (dI/dt)
L DE-10/350µs = (U SPARK – U 2 ) / (I max / 10 µs)
time
where U 2 = f(I max )
L DE-0.1kA/µs = (U SPARK – U 2 ) / (0.1kA/µs)
The required L DE is the higher value of both inductances LDE-10/350 and L DE-0.1kA/µs
Figure C.7 - Determination of decoupling inductance for 10/350 and 0.1kA/µs surges
62305-4 Ed. 1/CDV  IEC
– 85 –
Decoupling element
L DE = 8µH or 10µH
Surge
10/350
Sparkover at 1kV/µs: 4kV
Sparkover at DC:
2kV
Protected side
U DE , I DE
SPD2 MOV
SG SPD1
U1, I 1
U2, I 2
U REF (1mA) = 510 V
W max = 1 kJ
Figure C.8a - Circuit diagram of co-ordination for 10/350 surge
I[kA]
U[kV]
3.0
4.5
4.0
2.5
3.5
2.0
W [kJ]
1.25
Sparkover at 1 kV/µs: 4kV
W max = 1kJ
I SURGE ≈ I 2 (MOV)
1.00
3.0
1.5
2.0
1.5
1.0
0.75
Energy (MOV)
2.5
0.5
U 1 (SG)
1.0
0.5
0.25
0.5
0.0
0.0
0.0
0.5
1.0
1.5
2.0
0.00
t [ms]
Figure C.8b - Current/voltage/energy characteristics for L DE =8µH:
Energy co-ordination for 10/350 surge not achieved (SG not ignited)
I[kA] U[kV]
W [kJ]
3.0
2.5
2.0
1.5
1.0
0.5
0.0
4.5
Sparkover at 1 kV/µs: 4kV
4.0
3.5
W max = 1kJ
1.00
I SURGE ≈ I 1 (SG)
3.0
0.75
2.5
2.0
1.5
0.5
U 1 (SG)
1.0
0.5
0.0
0.0
1.25
0.25
Energy (MOV)
0.5
1.0
1.5
2.0
0.00
t [ms]
Figure C.8c - Current/voltage/energy characteristics for L DE =10µH:
Energy co-ordination for 10/350 surge achieved (SG ignited)
Figure C.8 - Example with SG and MOV for 10/350 surge
62305-4 Ed. 1/CDV  IEC
– 86 –
Decoupling element
L DE = 10µH or 12µH
Surge
0,1 kA/µs
Protected side
U DE , I DE
Sparkover at 1kV/µs: 4kV
SG SPD1
Sparkover at DC:
2kV
SPD2 MOV
U1, I 1
U2, I 2
U REF (1mA) = 510 V
W max = 1 kJ
Figure C.9a - Circuit diagram of co-ordination for 0.1kA/µs surge
I[kA] U[kV]
25
W [kJ]
3.0
3.5
Sparkover voltage of SG
3.0
2.5
20
2.5
2.0
15
1.5
10
2.0
I 2 (MOV)
1.5
U 1 (SG)
W max (1kJ)
1.0
5
1.0
0.5
0.5
Energy (MOV)
0.0
0.0
0
0
50
100
150
200
250
t [µs]
Figure C.9b - Current/voltage/energy characteristics for L DE =10µH:
Energy co-ordination for 0.1kA/µs surge not achieved
I[kA] U[kV]
25
W [kJ]
3.0
3.5
Sparkover voltage of SG
20
15
2.5
2.0
I 2 (MOV)
1.5
10
5
3.0
2.5
2.0
U 1 (SG)
1.5
W max (1kJ)
1.0
0.5
Energy (MOV)
0
0.0
0
50
100
150
200
1.0
0.5
0.0
250
t [µs]
62305-4 Ed. 1/CDV  IEC
– 87 –
Figure C.9c - Current/voltage/energy characteristics for L DE =12µH:
Energy co-ordination for 0.1kA/µs surge achieved
Figure C.9 – Example with SG and MOV for 0.1kA/µs surge
L1
R1
MOV SPD1
R2
MOV SPD2
L2
R3
L3
MOV SPD3
MOV SPD4
Equipment
to be
protected
U RES (SPD1) = U RES (SPD2) = U RES (SPD3) = U RES (SPD4)
Figure C.10 - Co-ordination variant I (voltage limiting type SPD)
MOV SPD1
MOV SPD3
MOV SPD2
MOV SPD4
Equipment
to be
protected
U RES (SPD1) < U RES (SPD2) < U RES (SPD3) < U RES (SPD4)
Figure C.11 – Co-ordination variant II (voltage limiting type SPD)
R1
SG SPD1
L1
MOV SPD2
R2
L2
MOV SPD3
R3
L3
MOV SPD4
U RES (SPD2) = U RES (SPD3) = U RES (SPD4)
Equipment
to be
protected
62305-4 Ed. 1/CDV  IEC
– 88 –
Figure C.12 – Co-ordination variant III (voltage switching and limiting type SPD)
Decoupling element
R
Input
terminal
L
Output
terminal
SPD
SPD
NOTE – The series impedance or the filter can be omitted, if the energy co-ordination is assured by other suitable
measures (e.g. co-ordination of the voltage/current characteristics or use of triggered SPDs).
Figure C.13 – Co-ordination variant IV (several SPD in one element)
Surge
Surge
generator
SPD 1
U OC
(out)
Open
circuit
U OC
(in)
I SC
(out) EUT
Short
circuit
Equipment
under test
SPD 2
Combination wave
generator
Conversion of U OC (out) and I SC (out) into an equivalent combination wave:
U OC (1,2/50 waveshape)
I SC (8/20 waveshape)
Zi = 2 Ω
Figure C.14 – Co-ordination according to the “let through energy” method
62305-4 Ed. 1/CDV  IEC
– 89 –
Annex D
(Informative)
Selection and installation of an SPD set
D.1 Selection of SPD
D.1.1 Selection with regard to protection level
Rated impulse voltage withstand level U w of equipment to be protected is defined in IEC 60664-1.
NOTE - Protective level should be compared with the resistibility of equipment tested under the same
conditions as SPD (overvoltages and overcurrent waveform and energy, energized equipments, etc). This
matter is under consideration.
Equipment is protected:
a) if its rated impulse withstand voltage U w is greater or equal to the protective level U p of the
SPD plus a margin necessary to take into account influence of connecting conductors as well
as effect of distance and of the loop between the SPD and the equipment.
A 20% margin may be considered sufficient to cover these points even if a detailed study is
preferable:
1,2 ⋅ U p ≤ U w
For example, for an SPD connected very close to the equipment to be protected, inductive
voltage drop ∆U on the connecting conductors will add to protection level U p of the SPD.
Therefore the resulting effective protection level is:
• Up + ∆U
for SPD limiting type;
• max (Up , ∆U)
for SPD switching type.
For voltage drop on the connecting conductors, ∆U = 1 kV per m length is assumed.
b) if it is energy co-ordinated with the upstream SPD
D.1.2 Selection with regard to location and to discharge current
SPDs shall withstand the discharge current expected at their installation point. Installation points
used in an SPD set may be (Figure 2b):
MB
Main distribution board at line entrance to LPZ 1 or boundary of LPZ 0A /1 or LPZ 0 B /1
SB
Secondary distribution board or boundary of LPZ 1/2 and higher
SA
Socket outlet close to apparatus or terminal of apparatus
The discharge current expected in the installation point can be determined according to IEC 623053, Annex B calculating the distribution of conducted and of induced surge currents based on the
LPL chosen. When the calculation is uncertain or difficult, the impulse current I imp of SPD (Class I
tested) should be not lower than 12,5 kA.
The
use
of
SPD
depends
on
their
withstand
capability,
classified
in
IEC
61643-1:
62305-4 Ed. 1/CDV  IEC
•
– 90 –
Class I tested SPD - Impulse current I imp
This type of SPD is usually installed at installation point MB. The required minimum impulse
current I imp of SPD shall cover the (partial) lightning current (typical 10/350 surge) to be
expected at the installation point MB according to E.1 and/or E.2.
•
Class II tested SPD - Nominal discharge current I n
This type of SPD is usually installed at installation point SB. Its use at installation point MB is
allowed only, if entering services are entirely within LPZ 0 B and/or current and energy
discharged by SPD do not exceed its capability. The required minimum nominal discharge
current I n of SPD shall cover the surges (typical current waveform 8/20) to be expected at the
installation point according to E.3.
•
Class III tested SPD - Open circuit voltage U oc
Class III tested SPD are tested with a combination wave generator. The required open circuit
voltage U oc of the generator shall be selected so, that the corresponding short circuit current I sc
will cover the surges (typical current waveform 8/20) to be expected at the installation point
according again to E.3.
D.2 Installation of SPD set
The efficiency of an SPD set depends not only on proper selection of SPD but mainly on proper
installation. Main aspects to be considered in installation of an SPD system are:
•
location of SPD;
•
connecting conductors;
•
protective distance (oscillation phenomena);
•
protective distance (induction phenomena).
D.2.1 Location of SPD
Location of SPD shall comply with D.1.2.
Location of SPD is mainly affected by:
•
need that protection will be effective whichever will be the type of lightning flash (direct to
structure or to line; to ground nearby structure or line);
•
opportunity to divert to ground overcurrent related to surges as close as possible to the
entrance point of line into the structure.
The first criterion to be considered is: The closer is an SPD to the entrance point of incoming line,
the greater is the number of apparatus protected by such SPD (economical advantage). Then the
second criterion should be checked: The closer is an SPD to the apparatus to be protected, the
better is protection (technical advantage).
SPD at installation point MB affect the following risk components (IEC 62305-2):
RB
physical damage due to flashes to the structure (valid for SPD at LPZ 1 entrance);
RV
physical damage due to flashes to an incoming line (valid for SPD at LPZ 1 entrance);
RC
failures due to flashes to the structure;
62305-4 Ed. 1/CDV  IEC
RW
RZ
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failures due to flashes to an incoming line;
failures due to flashes near to an incoming line.
SPD at installation points SB and SA affect the following risk components (IEC 62305-2):
failures due to flashes to the structure;
RC
RM
failures due to flashes near to the structure.
RW failures due to flashes to an incoming line;
failures due to flashes near to an incoming line.
RZ
D.2.2 Connecting conductors
Connecting conductors of SPD shall have the minimum cross-section S given in Table 1.
D.2.3 Protective distance l po due to oscillations
During the operation stage of an SPD, voltage line to earth is limited around U p at the location of
the SPD.
If the circuit between SPD and apparatus is too long, propagation of surges leads to oscillation
phenomena. In case of open-circuit at apparatus terminals, this can increase the overvoltage at
terminal of apparatus up to 2 ⋅ U p and failure of apparatus may occur even if U p ≤ U w was chosen.
The protective distance l po is the maximum length of the circuit between SPD and apparatus, for
which protection of SPD is effective for apparatus (taking into account oscillation phenomena and
capacitive load).
These data depend on SPD technology, installation rules as well as load capacity.
If U p < U w /2, protective distance may be disregarded.
D.2.4 Protective distance l pi due to induction phenomena
Lightning flashes to the structure or to ground nearby the structure induce an overvoltage in the
circuit loop between SPD and apparatus which adds to U p and thereby reduces efficiency of SPD.
Induced overvoltages increase with dimensions of loop (Line routing: length of circuit, distance
between PE and active conductors) and decrease with attenuation of magnetic field strength
(Shielding: spatial shielding, line shielding). As this induction phenomenon may be coupled with the
one of oscillation phenomena, it is difficult to give an analytic formula for this influence. General
rule is to minimize the loop between SPD and equipment when the magnetic field generated by
lightning is too high.
D.2.5 Co-ordination of SPD
According to IEC 61643-12 cascade of SPD in an SPD set shall be co-ordinated. The SPD
manufacturers shall provide sufficient information in their documentation about the way to achieve
co-ordination between SPD.
Identical SPD are effectively co-ordinated.
More information on SPD co-ordination are given in Annex C.
62305-4 Ed. 1/CDV  IEC
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Annex E
(Informative)
Surges due to lightning at different installation points
For dimensioning of SPD the threat due to surges at the particular installation point of these
components shall be determined. Surges can arise from (partial) lightning currents (typical current
waveform 10/350), from induction effects into installation loops and as remaining threat downstream
of SPD (typical current waveform 8/20). The threat due to these surges must be lower than the
withstand of the used components defined by adequate tests. For SPD such tests are given in IEC
60364-1: Class I test defines an impulse test current I imp defined via peak value, charge and specific
energy, which is comparable with the 10/350 surge. Class II test defines an impulse test current I n
8/20 and Class III test uses a combination wave test, defining the open circuit voltage U oc 1,2/50
and the short circuit current I sc 8/20 of an 2 Ω combination wave generator.
E.1 Surges due to flashes to the structure (source of damage S1)
Surges flowing through external conductive parts and entering services may be evaluated according
IEC 62305-3, Annex B.
For detailed calculations it should be mentioned, that several factors can influence the amplitude
and the waveshape of such surges:
•
the cable length can influence current sharing and time characteristics due to L/R-ratio
•
different impedances of neutral and phase conductors can influence current sharing
(especially if the N conductor is multiple grounded: If N, L1, L2, L3 have the same impedance,
each conductor will carry about 25% . For lower impedance of N compared with L1, L2, L3 the N
conductor may carry about 50% and L1, L2, L3 about 50% / 3 ≈ 17% only)
•
different transformer impedances can influence current sharing (This effect is negligible, if the
transformer is protected itself by SPD bypassing its impedance)
•
the relation of the conventional earthing resistances of the transformer and of the consumer
influences current sharing (the lower the transformer impedance, the higher is the surge current
flowing into the low voltage system)
•
parallel consumers cause a reduction of the effective impedance of the low voltage system
which may increase the partial lightning current flowing into this system.
E.2 Surges due to flashes to entering services (source of damage S3)
For lightning flashes (typical waveform 10/350) direct to entering services, partitioning of the
lightning current in both directions of the service and breakdown of insulation to ground must be
taken into account. Therefore the threat in this case is usually lower than for lightning flashes direct
to the structure .
NOTE – Surges from source of damage S4 (flashes near to services) are much lower than those from S3 and may be
therefore neglected.
E.3 Secondary surges downstream of SPD and due to induction effects
Downstream of the SPD installed at service entrance (boundary of LPZ 0/1) the energy of surges is
strongly reduced and the waveform changes to shorter impulses (typical current waveform is 8/20).
Nevertheless, surges arise as remaining threat at the output of these SPD and can be even
amplified again due to induction effects from magnetic fields, generated either from nearby lightning
flashes (source S2) or from lightning current flowing in the external LPS or in the spatial shield of
LPZ 1 (source S1). Such surges are to be considered close to or at terminal of apparatus inside of
LPZ 1 and at boundary of LPZ 1/2.
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E.3.1 Surges inside of an unshielded LPZ 1
Inside an unshielded LPZ 1 (e.g. protected only by an external LPS according to IEC 62305-3 with
mesh width greater than 5 m) relatively high surges are to be expected due to high remaining threat
downstream of Class I tested SPD combined with the induction effects from the non damped
magnetic field.
E.3.2 Surges inside shielded LPZs
Inside of LPZs with effective spatial shielding (requiring mesh width below 5m according to IEC
62305-4 Annex A) generation of surges due to induction effects from magnetic fields is strongly
reduced. In such cases the surges are much lower than those given in E.3.1
Inside LPZ 1 remains the threat downstream of Class I tested SPD, but the induction effects are
lower due to the damping effect of its spatial shield.
Inside LPZ 2 the surges are further reduced due to lower threat downstream of Class II or Class III
tested SPD and due to the cascaded effect of both spatial shields of LPZ 1 and LPZ 2.