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SUBPROJECT: OFFSITES
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AREA: GENERAL
PHASE: DETAILED ENGINEERING
DISCIPLINE: ELECTRICAL
TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION FOR DA-1 &
2 UNITS
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RPLC DEEP CONVERSION PROJECT
GROUNDING AND LIGHTNING SYSTEM CALCULATION
FOR DA-1 & DA-2 UNITS
REFINING MAJOR PROJECTS GENERAL MANAGEMENT
PROJECT: RPLC DEEP CONVERSION PROJECT
SUBPROJECT: OFFSITES
UNIT: ATMOSPHERIC DISTILLATION UNIT U-04 AND UNIT U-05
AREA: GENERAL
PHASE: DETAILED ENGINEERING
DISCIPLINE: ELECTRICAL
TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION FOR DA-1 &
2 UNITS
PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
PDVSA DOC. No.
3006-400A-DE426902
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DATE: 27-09-13
PAGE 3 OF 61
Contents
1
SCOPE ................................................................................................................................................ 4
2
OBJECTIVE ........................................................................................................................................ 4
3
REFERENCE ...................................................................................................................................... 4
4
DEFINITIONS ...................................................................................................................................... 5
5
TERMS ................................................................................................................................................ 6
5.1 IEEE 80 ............................................................................................................................................... 6
5.2 PIP PCCEL001 .................................................................................................................................... 7
6
SPECIFICATIONS FOR GROUNDING DESIGN ................................................................................. 7
6.1 Grounding Electrodes ....................................................................................................................... 7
6.2 Maximum Fault Current ..................................................................................................................... 8
6.3 Soil Resistivity ................................................................................................................................... 9
6.4 Electrical Protection Operation Time ............................................................................................... 9
6.5 Conductor Sizing Calculation ........................................................................................................... 9
6.6 Rod Resistance to Ground and Maximum Density Current Calculations ................................... 10
6.7 Grounding Bus Bar.......................................................................................................................... 12
7
SIMULATIONS .................................................................................................................................. 12
8
SUMMARY ........................................................................................................................................ 15
9
RESULTS AND RECOMMENDATIONS ........................................................................................... 16
10 LIGHTNING PROTECTION CALCULATION .................................................................................... 16
10.1 Terms, NFPA 780 .............................................................................................................................. 16
10.2 References ....................................................................................................................................... 17
10.3 Keraunic Level and Lightning Flash Density................................................................................. 17
10.4 Protection Philosophy ..................................................................................................................... 17
11 CONCLUSIONS AND RECOMMENDATIONS ................................................................................. 19
12 ATTACHMENTS ............................................................................................................................... 19
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DATE: 27-09-13
PAGE 4 OF 61
SCOPE
The scope of this document is limited to the grounding and lightning system calculation design
of Atmospheric Distillation Unit 04 and Unit 05.
2
OBJECTIVE
The objective of this document is to present the criteria, methodology and calculation use to
design the grounding and lightning systems in Atmospheric Distillation Unit 04 and Unit 05,
required at permanent facilities for the RPLC Deep Conversion Project in Puerto La Cruz
Refinery of PDVSA, Venezuela.

3
Grounding and lightning systems will be designed to achieve the following objectives:
To assure that a person in vicinity of grounded facilities will not be exposed to a critical
electrical shock, by keeping touch and step voltages under tolerable levels as per IEEE 80.

To provide means to carry electric currents into the earth under fault conditions without
exceeding any operating limits or adversely affecting continuity of service without creating a
fire or explosive hazards.

To assure that a person, equipment, or structures in DA-1 and DA-2 areas will be protected
against lightning discharges.
REFERENCE
(1)
Codes and Regulations
•
National Electrical Code NFPA 70 2011.
•
IEEE Std 80 - 2000 IEEE Guide For Safety in AC Substation Grounding.
•
IEEE 142 IEEE Recommended Practice for Grounding of Industrial and Commercial
Power Systems.
•
PIP PCCEL001 Instrumentation Electrical Design Criteria
•
NFPA 70 (2011) National Electrical Code.
•
PDVSA N 201 (1993) Obras Eléctricas.
(2)
Project Documents
•
GENERAL SPECIFICATION FOR ELECTRICAL SYSTEM AND INSTALLATION
N° 3006-5000-DE115001.
•
SHORT-CIRCUIT STUDY FOR DA-1 & 2 UNITS
N° 3006-400A-DE322901
•
CABLE LIST DA-1 UNIT
N° 3006-404A-DE707001
•
CABLE LIST DA-2 UNIT
N° 3006-405A-DE707001
•
ELECTRICAL PROTECTION COORDINATION STUDIES FOR DA-1 & 2 UNITS
N° 3006-400A-DE321902
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TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION FOR DA-1 &
2 UNITS
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PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
4
DATE: 27-09-13
•
ELECTRICAL PROTECTION COORDINATION STUDIES DA-2 UNIT
N° 3006-405A-DE321001
(3)
Project Drawings
•
PLOT PLAN UNIT 04
N° 3006-404A-DM206001
•
PLOT PLAN UNIT 05
N° 3006-405A-DM206001
•
KEY LINE DIAGRAM
N° 3006-404A-DE216001
•
KEY LINE DIAGRAM
N° 3006-405A-DE216001
•
INSTALLATIONS DETAILS -GROUNDING & LIGHTNING FOR DA-1 & DA-2 UNITS
N° 3006-400A-DE272901
•
HAZARDOUS AREA CLASSIFICATION
DISTILLATION UNIT 1 (DA-1) REVAMP
N° 3006-404A-DE217001
DRAWING
UNIT
04
ATMOSPHERIC
•
HAZARDOUS AREA CLASSIFICATION
DISTILLATION UNIT 2 (DA-2) REVAMP
N° 3006-405A-DE217001
DRAWING
UNIT
05
ATMOSPHERIC
(4)
Others supplied by Hyundai
•
AIG-2012-531-CT-02_Resistivity Test Results. See Annex A.
•
02. Borehole Location Plan_Rev.1. See Annex A.
•
Short Circuit Calculation N° 3006-500A-DE322001
•
Electrical Grounding Philosophy N° 3006-500A-DE272401
•
Instrument Grounding Philosophy N° 3006-500A-DI2C6011
•
Earthing & Lightning Protection Calculation N° 3006-500A-DE426002
DEFINITIONS
1)
COMPANY:
PDVSA, Petróleos, S.A.
2)
MAIN PROJECT: Engineering, Procurement, Construction and Start Up Assistance of the
Environmental Units, Auxiliary Units and Revamp of the Atmospheric
Distillation Units of the Deep Conversion Project, Puerto La Cruz
Refinery
3)
PROJECT:
4)
CONTRACTOR: A consortium formed by HYUNDAI ENGINEERING & CONSTRUCTION
CO., LTD., HYUNDAI ENGINEERING CO., LTD., and WISON
ENGINEERING LTD. who is the EPC Contractor for the MAIN
PROJECT.
Detail engineering service for DA-1 & DA-2 Units
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DISCIPLINE: ELECTRICAL
TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION FOR DA-1 &
2 UNITS
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PDVSA DOC. No.
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PAGE 6 OF 61
5)
SUBCONTRACTOR:
INELECTRA S.A.C.A.
6)
CONFEED:
A consortium formed by JGC, INELECTRA and CHIYODA, who is the
contractor for the RPLC Deep Conversion Project Phase II.
7)
RPLC:
Refinery Puerto La Cruz
8)
SOC:
Seoul Operation Center
9)
PMT:
Project Management Team
10) PMC:
Project Management Consultant as a member of COMPANY and Toyo
Engineers
11) DHT:
Document Handling Team
12) Project Space:
CONTRACTOR’s EDMS
13) SIMDE:
COMPANY’s EDMS
14) PM:
Project Manager
15) EM:
Engineering Manager
16) SE:
Senior Engineer
17) JE:
Junior Engineer
18) LD:
Lead Discipline Engineer
19) DC:
Document Controller
20) DRN:
Design Review Notice
5
TERMS
5.1
IEEE 80
Auxiliary ground electrode: A ground electrode with certain design or operating constraints. Its
primary function may be other than conducting the ground fault current into the earth.
Fault current division factor (Sf): A factor representing the inverse of a ratio of the symmetrical
fault current to that portion of the current that flows between the grounding grid and surrounding
earth.
Ground: A conducting connection, whether intentional or accidental, by which an electric circuit
or equipment is connected to the earth or to some conducting body of relatively large extent that
serves in place of earth.
Grounded: A system, circuit, or apparatus provided with ground for the purposes of establishing
a ground return circuit and for maintaining its potential at approximately the potential of earth.
Ground Current: A current flowing into or out of the earth or its equivalent serving as a ground.
Ground Electrode: A conductor imbedded in the earth and used for collecting ground current
from or dissipating ground current into the earth.
Ground Potential Rise (GPR): The maximum electrical potential that a substation grounding grid
may attain relative to a distant grounding point assumed to be at the potential of remote earth.
Ground Return Circuit: A circuit in which the earth or an equivalent conducting body is utilized to
complete the circuit and allow current circulation from or to its current source.
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Grounding Grid: A system of horizontal ground electrodes that consists of a number of
interconnected, bare conductors buried in the earth, providing a common ground for electrical
devices or metallic structures, usually in one specific location.
Grounding System: Comprises all interconnected grounding facilities in a specific area.
Step Voltage: The difference in surface potential experienced by a person bridging a distance of
1 m with the feet without contacting any grounded object.
Surface Material: A material that covers the soil with the purpose to reduce the step and touch
voltages. Generally this material has a high resistivity.
Symmetrical Grid Current (Ig): That portion of the symmetrical ground fault current that flows
between the grounding grid and surrounding earth.
Symmetrical Ground Fault Current (If): The maximum rms value of symmetrical fault current
after the instant of a ground fault initiation. As such, it represents the rms value of the
symmetrical component in the first half-cycle of a current wave that develops after the instant of
fault at time zero.
Touch Voltage: The potential difference between the ground potential rise (GPR) and the
surface potential at the point where a person is standing while at the same time having a hand in
contact with a grounded structure.
Transferred Voltage: A special case of the touch voltage where a voltage is transferred into or
out of the substation from or to a remote point external to the substation site.
5.2
PIP PCCEL001
AC Safety Ground: The grounding system required by NEC Article 250 to provide protection for
personnel and electrical equipment. The instrument ground bus is connected to the safety
ground in accordance with NEC requirements.
Field Instrument Enclosure: The term used in the generic sense to indicate a cabinet or building
that houses instruments and/or wiring termination external to instrument rooms or control
buildings.
Instrument Ground System (IGS): Instrumentation ground system connected to a high-quality
earth ground and isolated from all other grounds.
Instrument Rooms: The term used in the generic sense for a walk-in-type structure, including
rack rooms, remote instrument enclosures, or any completely enclosed structure that houses
control equipment.
Junction Box: A protective enclosure around connections between electric wires or cables. The
junction box may be a field junction box (JB) or it may be within a control building or instrument
enclosure, where it is referred to as an interface box (IB) or marshalling cabinet.
6
6.1
SPECIFICATIONS FOR GROUNDING DESIGN
Grounding Electrodes
According to document N° 3006-5000-DE115001 “General Specification for Electrical System
and Installation”, a grounding grid shall be provided as the general grounding electrode. This
grounding grid shall be of bare copper conductors, buried at minimum of 0.45 meters below
grade level.
According to document N° 3006-5000-DE115001 “General Specification for Electrical System
and Installation” and drawing N° 3006-500A-DE272401 “Electrical Grounding Philosophy” the
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cable size of the main grounding grid shall be a minimum of 2/0 AWG (70 mm2), and a minimum
cable size of 2 AWG (35 mm2) for derivations. The cable size of the main grounding grid for
building substation shall be 250 MCM. Size of cable intended for grounding grid for packaged
substation is to be confirmed. Nevertheless 250 MCM also is to be assumed.
Grounding rods shall be a minimum of 5/8 inch of diameter and 8 feet length.
The underground connections between the main ground grid and the derivations shall be
exothermic type. Compression and mechanical connectors shall be used for aboveground
connections. It is recommended exothermic connections for download conductors intended for
lightning systems.
Exothermic connections shall not be done in areas where flammable liquids or explosive vapors
are present or thought to be present. In the latter case, a combustible gas indicator test shall be
made to assure that the area is safe i.e. the explosimeter reading shall be zero.
The constructive characteristics are shown in the document N° 3006-400A-DE272001
“Grounding and Lightning Installation Details”.
The conductors will have current capacity and mechanical strength to be able to connect to:
6.2

All non-energized metallic structures that accidentally might be, such as: transformers
cases, motor frames and skids, cable trays, ducts, vessels, fences, tanks and any other
miscellaneous supporting structures.

Lightning rods, surge suppressors, control and lighting circuits, neutral of transformers, etc.
Maximum Fault Current
Maximum one-phase short circuit level is at SS98-2C-SWG-501 (34.5 kV) and equals 0.8 kA
(bus-tie breaker closed) according to information indicated in PDVSA Doc. No.
3006-500A-DE322001 Rev. A supplied by Hyundai. One-phase short circuit level at 4.16 kV is
0.4 kA for all study cases according to information indicated in PDVSA Doc. No.
3006-400A-DE322901 Rev. A. Maximum one-phase short circuit level is at SS04-MCC-202A
(0.48 kV) and equals 46.86 kA for case 5 (worst operating condition), also according to
information indicated in PDVSA Doc. No. 3006-400A-DE322901 Rev. A.
All these one phase short circuit currents will return via its equipment grounding conductor or
through the grounding mesh, according to information shown in CABLE LIST DA-1 UNIT
3006-404A-DE707001 and CABLE LIST DA-2 UNIT 3006-405A-DE707001. There are no
expected ground currents to flow into the soil, neither from any near overhead distribution line
nor from any other source. So fault current division factor is assumed to be zero.
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6.3
DATE: 27-09-13
PAGE 9 OF 61
Soil Resistivity
According to document AIG-2012-531-CT-02_Resistivity Test Results, there are four two-layer soil
resistivity models, calculated for process and buildings of interest: two (2) models for DA-1 & two
others for DA-2.
Table 1. Electrical Resistivity Models for DA-1.
Point ERT 01
PROCESS AREA DA‐1
322,643 E; 1,129,635 N
Depth (m)
Resistivity (Ω*m)
0 ‐ 3.6
11.5
> 3.6
2.4
Point ERT 03
SS04 & SRG04
322,605 E; 1,129,711 N
Depth (m)
Resistivity (Ω*m)
0 – 2.1
25.2
> 2.1
22.3
Study points coordinates are UTM
Table 2. Electrical Resistivity Models for DA-2.
Point ERT 05
PROCESS AREA DA‐2 & SRG05
322,882 E; 1,129,322 N
Depth (m)
Resistivity (Ω*m)
0 – 0.5
9.5
> 0.5
8.03
Point ERT 06
SS05
322,869 E; 1,129,326 N
Depth (m)
Resistivity (Ω*m)
0 ‐ 1.04
45.2
> 1.04
8.1
Study points coordinates are UTM
Complete resistivity results are shown in Annex A.
6.4
Electrical Protection Operation Time
The fault duration shall correspond to maximum fault clearing time of backup protections, which
comprises the moment of fault occurrence until the fault clearance. For this period of time it was
assumed 0.25 s at all voltage levels (IEEE Std. 80-2000 Sec 16.2.2). Nevertheless, the assumption
of this period of time corresponds to the expected value.
When the electrical protection coordination studies are issued, further examination of fault clearance
times is needed to confirm actual cross sectional area of transformers neutral groundings, actually
rated at 2/0 AWG in the Electrical Grounding Philosophy, and neutral groundings of diesel
generators, also rated at 2/0 AWG in the Electrical Grounding Philosophy N°
3006-500A-DE272401.
6.5
Conductor Sizing Calculation
Considering the short time temperature rise in a ground conductor, its minimum sizing is determined
by the formula (see IEEE Std 80 – 2000, sec. 11.3.1.1, Equation 41):
A
197.4
=I
∗
Where:
Akcmil = conductor cross section, (kcmil)
∗
∗ ln
0
0
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Tm = maximum allowable temperature, (°C)
Ta= ambient temperature, (°C)
PAGE 10 OF 61
1083 °C
40 °C
αr = thermal coefficient of resistivity at reference
temperature Tr, (1/°C)
Tr = reference
constants, (°C)
DATE: 27-09-13
temperature
for
0.00393 °C-1
material
20°C
ρr = resistivity of the ground conductor at
reference temperature Tr, (µΩ-cm)
1.72 µΩ-cm
K0= (1/ αr)-Tr, (°C)
234°C
tc = duration of the current, (s)
0.25s
TCAP = thermal capacity per unit volume from
Table 1, (J/cm3°C)
3.42 J/cm3°C
Note that αr and ρr are both defined at the same reference temperature of Tr. Table 1 (see IEEE Std
80 – 2000, sec. 11.3.1.1) provides data for αr and ρr at 20°C.
Akcmil = 164.1 kcmil
Result indicates that the grounding conductor must have a minimum size of 164.1 kcmil (4/0 AWG),
equivalent to 83.13 mm2. This size does not take into account the decrement factor. This value is
greater than the one indicated in the Electrical Grounding Philosophy for LV transformers where
actual cross sectional area of transformers neutral grounding is rated at 2/0 AWG. Further
examination of fault clearance times is needed to validate this area.
6.6
Rod Resistance to Ground and Maximum Density Current Calculations
Grounding systems usually consist of local electrodes placed from the grid into the soil in order to
reach deeper layers. For any given 5/8” diameter and 2.4 m length rod, its resistance is:
Rrod 
  4* L  

*  Ln
  1
2 *   L   R  
Where:
Rrod = Resistance of any given rod (W)
r = Average resistivity, (Ω*m)
Given in Table 3
L = Length of rod, (m)
2.4 m
R= Radius of rod, (m)
0.0079375 m
As stated in 6.3 resistivity values are expressed in a two-layer model of soil. But the resistance
equation is given as a function of a resistivity. To account for this, IEEE 80 suggests using an
average value of resistivity in order to compute with this equation. Average values are given below
for all cases.
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Table 3. Average Electrical Resistivity for DA-1/DA-2.
Point ERT 01
PROCESS AREA DA‐1
322,643 E; 1,129,635 N
Point ERT 03
SS04 & SRG04
322,605 E; 1,129,711 N
Average Resistivity (Ω*m)
=(11.5+2.4)/2=6.95
Average Resistivity (Ω*m)
=(25.2+22.3)/2=23.75
Point ERT 05
PROCESS AREA DA‐2 & SRG05
322,882 E; 1,129,322 N
Point ERT 06
SS05
322,869 E; 1,129,326 N
Average Resistivity (Ω*m)
=(9.5+8.03)/2=8.675
Average Resistivity (Ω*m)
=(45.2+8.1)/2=26.65
Resistance for any individual rod follows:
Table 4. Resistance of one rod as a function of its location in DA-1/DA-2.
Point ERT 01
PROCESS AREA DA‐1
322,643 E; 1,129,635 N
Point ERT 03
SS04 & SRG04
322,605 E; 1,129,711 N
Rod Resistance (Ω) = 2.81
Rod Resistance (Ω) = 9.60
Point ERT 05
PROCESS AREA DA‐2 & SRG05
322,882 E; 1,129,322 N
Point ERT 06
SS05
322,869 E; 1,129,326 N
Rod Resistance (Ω) = 3.51
Rod Resistance (Ω) =10.78
All values of grounding rods are lower than maximum NEC limit of 25 Ω per one electrode. All
multiple rods shall meet restrictions given in “Electrical Grounding Philosophy” N°
3006-500A-DE272401 Notes 6 & 7 and in GENERAL SPECIFICATION FOR ELECTRICAL
SYSTEM AND INSTALLATION N° 3006-5000-DE115001 Sec. 13.3.9.
Another condition to be met is the maximum current density around any rod. This is compute using
equation 4.2 of IEEE 142, as follows:
I max 
Where:
dImax = Maximum density current (A/m)
1140 * d
 *t
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UNIT: ATMOSPHERIC DISTILLATION UNIT 1 (U-04) AND UNIT 2 (U-05)
AREA: GENERAL
PHASE: DETAILED ENGINEERING
DISCIPLINE: ELECTRICAL
TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION
PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
PDVSA DOC. No.
3006-400A-DE426902
VONE DOC. No.
N/A
REV. P2
DATE: 27-09-13
PAGE 12 OF 61
t = duration of the current, (s)
d= rod diameter (mm)
0.25 s
15.875 mm
Worst case for any of the above points is the one with less resistivity e.g. ERT 01. For this case Imax
= 1.37 kA/m which shall be use as the maximum density current in order to keep the current density
in the earth to a low value.
6.7
Grounding Bus Bar
6.7.1
Plant/Safety Grounding Bar
PG bus bar shall be used to ground equipment cases, instrument enclosures, panel boards and rack
rooms placed inside process-instrument buildings, analyzer house or other buildings and for
process-field instruments. Other grounding bars shall be allocated each 30 meters minimum in
process areas.
6.7.2
Instrument Grounding bar (IG)
IG bus bar shall be used to connect the instrument ground system (IGS) isolated from all other
grounds. It shall be connected at one point to a high-quality earth ground (a ground rod arrangement
placed for instance in a triangular configuration); each rod will have a grounding test well, and shall
also be connected at one point to the main grounding grid.
6.7.3
Intrinsically Safe Grounding bar (ISG)
Similarly, ISG bus bar shall be used to ground intrinsically safe instrument equipment. It also shall
be connected at one point to a high-quality earth ground (a ground rod arrangement placed for
instance in a triangular configuration); each rod will have a grounding test well, and shall also be
connected at one point to the main grounding grid.
These criteria meet the “Electrical Grounding Philosophy” N° 3006-500A-DE272401.
7
SIMULATIONS
The simulations were made using the commercial software ETAP 7.5.0. The software uses a two
layer soil model, the faulted current along with the expected clearing time to calculate the grounding
grid resistance according to a given electrode arrangement, calculates GPR and evaluates the
dangerous points where surface voltage profiles are greater than maximum tolerable voltages.
The DA-1 and DA-2 grounding grids have an irregular pattern. For that reason calculations were
made using the Finite Element option available in ETAP, recommended for non regular grids
configurations.
Figures 1 to 7 show the arrangement of conductors and grounding rods for all substations.
REFINING MAJOR PROJECTS GENERAL MANAGEMENT
PROJECT: RPLC DEEP CONVERSION PROJECT
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AREA: GENERAL
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DISCIPLINE: ELECTRICAL
TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION
PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
Figure 1. ETAP Graphical Interface for SS04.
Figure 2. ETAP Graphical Interface for SRG04.
PDVSA DOC. No.
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DATE: 27-09-13
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REFINING MAJOR PROJECTS GENERAL MANAGEMENT
PROJECT: RPLC DEEP CONVERSION PROJECT
SUBPROJECT: OFFSITES
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AREA: GENERAL
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DISCIPLINE: ELECTRICAL
TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION
PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
Figure 3. ETAP Graphical Interface for SS05.
Figure 4. ETAP Graphical Interface for SRG05.
PDVSA DOC. No.
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AREA: GENERAL
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DISCIPLINE: ELECTRICAL
TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION
PDVSA DOC. No.
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REV. P2
DATE: 27-09-13
PAGE 15 OF 61
PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
Figure 5. ETAP Graphical Interface for CCM DA-2.
8
SUMMARY
Below are two tables that summarize the physical characteristics of the grounding system for each
substation and area.
Table 5. Summary of the Grounding System for SS04, SS05 & CCM.
UNIT
SS04
SS05
CCM DA‐2
Etouch (Tolerable) Estep (tolerable)
Short
Area (m2) (Horizontal Conductor of
Mesh
Total Ground
Ground
Circuit (kA)
x Vertical)
Size (MCM) Interval (m) Wire Lenght (m) Resistivity (ohm) Em (Calculated)
Es (Calculated)
0
0
0
40m x 24m
18m x 30m
12m x 10m
500
250
500
4m x 4m
6m x 6m
2m x 2m
544m
228m
142m
0.31
0.22
0.28
240.8
267.1
0
0
247.7
294.9
0
0
235.3
245.2
0
0
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TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION
PDVSA DOC. No.
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VONE DOC. No.
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REV. P2
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PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
Table 6. Summary of the Grounding System for DA-1/DA-2, SRG04 & SRG05.
9
UNIT
Total Ground Ground
Area (m2) Conductor Size (AWG) Wire Lenght Resistivity
(m)
(ohm)
DA‐1
21594.39
#2/0
1105m
0.31
36
DA‐2
689249.5
#2/0
793m
0.31
44
SRG04
1338.85
#2/0
150m
0.37
9
SRG05
112.77
#2/0
109m
0.17
6
# of Rods
RESULTS AND RECOMMENDATIONS
No currents will be flowing from the designed grounding grid into the earth so the rise of the grid
potential with respect to remote earth is zero and consequently there are no expected values of step
and touch voltages inside the area.
Though, it is recommended to validate this information with design data from the main substation at
230 kV to analyze if there may exist transferred potentials either from the main substation grid or
interconnected substations grids inside the refinery to the SS-98 2B ground grid, that can affect the
SS-04 and/or SS-05 step and touch potentials.
Simulation results indicates that the grounding grid resistance of DA-1 equals Rg=0.03 W and for
DA-2 is Rg=0.05 W. Grounding grid resistance of SS04 is Rg=0.31 W and for SS05 is Rg=0.22 W.
Similar results for grounding grid resistance of SRG04 which is Rg=0.37 W, that of SRG05 which is
Rg=0.17 W and that of CCM which is Rg=0.28 W Complete simulation results are shown in
Attachment B.
The grounding grids resistances values are low compare to known values of industrial ground grids,
due to low soil resistivity. In all cases the addition of grounding rods will reduce even more the total
resistance of the grids. This can be seen from tables 1 & 2, where resistivity values in deeper layers
are even lower than near surface.
The interconnection with other grids inside the refinery will improve the grounding system.
10
10.1
LIGHTNING PROTECTION CALCULATION
Terms, NFPA 780
Lightning flash density (Ng): The yearly number of flashes to ground per square kilometer (flashes/
Km2/ year).
Rolling sphere method: This is a model based on the simple electrogeometric method. To apply the
method, an imaginary sphere is rolled over the structure. All surface contact points are deemed to
require protection, while the unaffected surfaces and volumes are deemed to be protected. This
method is explained in NFPA 780 2011.
Air Terminal or Strike termination device: A component of a lightning protection system that
intercepts lightning flashes and connects them to a path to ground. Strike termination devices
include air terminals, metal masts, permanent metal parts of structures, and overhead ground wires
installed in catenary lightning protection systems.
REFINING MAJOR PROJECTS GENERAL MANAGEMENT
PROJECT: RPLC DEEP CONVERSION PROJECT
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DISCIPLINE: ELECTRICAL
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PDVSA DOC. No.
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PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
10.2
10.3
DATE: 27-09-13
PAGE 17 OF 61
References
(1)
Codes and regulations
•
National Electrical Code NFPA 70 2011.
•
PDVSA N 201 1993 Obras Eléctricas.
•
NFPA 780 2011 Standard for the Installation of Lightning Protection Systems.
(2)
Project Documents
•
General Specification for Electrical System and Installation Doc. N° 3006-5000-DE115001.
(3)
Project Drawings
•
Plot Plan Unit 04 N° 3006-404A-DM206001
•
Plot Plan Unit 05 N° 3006-405A-DM206001
•
Grounding and Lightning Installation Details N° 3006-400A-DE272001
(4)
Others
•
Actualización de la actividad de rayos en Venezuela, empleando la información del proyecto
satelital de la Nasa. Junio 2009. L. Díaz, M. Martínez, J. Ramírez, J. Rodríguez.
Keraunic Level and Lightning Flash Density
Keraunic level value according to document “Actualización de la actividad de rayos en Venezuela,
empleando la información del proyecto satelital de la Nasa” is considered to be 13 (thirteen)
thunderstorm days per year.
To compute the lightning flash density, the following equation given by IEEE Std. 998-1996 is used.
0.12
1.56
/
/
Where:
NG = lightning flash density
TD = thunderstorm days per year
10.4
Protection Philosophy
Lightning protection shall be designed according to NFPA standard 780, which applies the rolling
sphere method to compute its distances. Facilities located inside protected areas will be considered
adequately protected against lightning strokes. These protected areas are buildings, pipe racks, air
cooler bays and platforms, if they meet grounding requirements. Above platforms equipment
operating under pressure if meet their grounding requirements and its metal thickness greater than
4.8 mm need no lightning design.
Packaged substations lightning system shall be design and installed by package vendor.
10.4.1
Substations
Package substations lightning systems design are beyond the scope of this document. Vendor shall
protect their transformers yards using air terminals. SRG buildings also shall be protected using
Franklin rods installed on the top of them.
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DISCIPLINE: ELECTRICAL
TITLE: GROUNDING AND LIGHTNING SYSTEM CALCULATION
PDVSA DOC. No.
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PDVSA PROJECT NO.: 3006; VONE PROJECT NO.: VPLC
10.4.2
DATE: 27-09-13
SRG04, SRG05 and CCM DA-2 Lightning Protection System
Lightning protection of these buildings consists of air terminals, spaced at a distance no greater than
7.6 m since its rod length is 24 in (0.6 m). Limiting distances found in Sec. 4.6.2.1, 4.8.1, 4.8.1.2,
4.8.3 and in Figure 4.8.3(a) are accomplished in SRG04 and SRG05 lightning design.
Corresponding drawings are shown in Attachment D.
10.4.3
Pipe Rack Structures
The metal framework of a pipe rack structure shall be permitted to be utilized as the main conductor
of a lightning protection system if it is thicker than 4.8 mm and electrically continuous (NFPA 780
2011 Sec 4.16.1). Also pipe racks shall be connected to ground at each 40 meters minimum
according to document “General Specification for Electrical System and Installation”.
10.4.4
Heater B-0501
The heater located in unit 05 is classified as heavy duty, according to NFPA 780 2011 Sec 6.1, due
to the fact that the cross-sectional area of the flue is greater than 0.3 m2 and its height is greater than
23 m. The materials shall be class II as shown in Table 7.
Table 7 Minimum class II material requirements (NFPA 780 2011 Sec 4.1.1.1.2).
Type of conductor
Air terminal, solid
Parameter
Diameter
Cooper
SI
US
SI
US
12.7 mm
1/2 in
15.9 mm
5/8 in
Size each
strand
Main conductor,
cable
15 AWG
13AWG
Weight per
length
558 g/m
0.375
lb/ft
283 g/m
0.190
lb/ft
Cross-section
area
58 mm2
2/0 AWG
97 mm2
4/0 AWG
Size each
strand
Bonding
conductor, cable Cross-section
area
(solid or stranded)
Bonding
Thickness
1.30 mm
conductor, solid
strip
Width
12.7 mm
Main conductor,
solid strip
Aluminum
17 AWG
14 AWG
6 AWG
4 AWG
0.051 in
1/2 in
1.63 mm
0.064 in
12.7 mm
1/2 in
Thickness
1.63 mm
0.064 in
2.61 mm 0.1026 in
Cross-section
area
58 mm2
2/0 AWG
97 mm2
4/0 AWG
If metal structures as metal platforms, ladders, and other metal bodies are inherently bonded
through construction shall not require further bonding. Metal bodies located in the heater system
without an inherently connection shall be bonded to the structure using materials of the
aforementioned table.
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If these heavy-duty metal stacks have a metal thickness higher of 4.8 mm they neither require air
terminals nor down conductors (NFPA 780 2011 Sec 6.10.1). Metal stacks shall be grounded by at
least two grounding electrodes as equally spaced as practicable around the stack.
If metal guy wires and cables are used to support stacks, these last shall be grounded at their lower
ends.
B-0501 vendor shall confirm if these conditions are met for the heater in order to be considered self
protected. The sufficient condition that shall meet the equipment since it is classified as a hazardous
area class I, division 2 (N° 3006-405A-DE217001) is that any openings where flammable
concentrations of vapor or gas escape to the atmosphere shall be closed or protected against the
entrance of flame.
Otherwise, the vendor shall design and install a lightning system according to NFPA 780 Sec. 6
requirements.
11
CONCLUSIONS AND RECOMMENDATIONS
According to the results obtained from grounding calculations, there are no expected values of step
and touch voltages. Also, the grounding grids resistance values are low, which brings an alternative
low resistance path to fault currents. These results correspond to design values indicated in the
Electrical Grounding Philosophy and the General Specification for Electrical System and
Installation.
Results also indicates that the grounding conductor must have a minimum size of 164.1 kcmil (4/0
AWG), equivalent to 83.13 mm2 (not taken into account the decrement factor) for maximum
one-phase short circuit level at SS04-MCC-202A (0.48 kV) which equals 46.86 kA. This value is
greater than indicated in the Electrical Grounding Philosophy and the General Specification for
Electrical System and Installation for LV transformers, where actual cross sectional area of
transformers neutral grounding is rated at 2/0 AWG.
Further examination of fault clearance times is needed to confirm actual cross sectional area for
transformers neutral groundings and neutral groundings of diesel generators.
It is recommended to validate this design with design data from the main substation at 230 kV to
analyze if there may exist transferred potentials either from the main substation grid or
interconnected substations grids inside the refinery to the SS-98 2B ground grid, that can affect
substations step and touch potentials.
12
ATTACHMENTS
ATTACHMENT A. RESISTIVITY RESULTS
ATTACHMENT B. ETAP SIMULATION RESULTS
ATTACHMENT C. GROUNDING DRAWINGS
ATTACHMENT D. LIGHTNING DRAWINGS