brazil event march 2018

2019 International Conference on Intelligent Green Building and Smart Grid (IGBSG2019), 6-9 Sept., Yichang
China
Analysis of Brazilian blackout on March 21st,2018
and revelations to security for Hunan Grid
Yongyan Liu
State Grid Hunan Electrical Power Company Limited Research Institute
Changsha, China
[email protected]
Abstract—Brazil ±800kV Xingu convertor station’s
technical defects lead to chain reaction in Brazil
that a Brazilian nationwide blackout accident
happened on March 21st, 2018. This blackout
severely impact the north and northeast of Brazil
including 14 states. In this paper, the general
situation of Brazilian power grid is introduced. And
the occurrence and propagation of the blackout are
retrospected. Furthermore, the main reason of the
blackouts are analyzed in this article. According to
the Brazilian blackout, Qishao DC is evaluated
from the relay protection, configuration of security
and stability equipment and strategy analysis of
power plants’ primary frequency regulation.
Combined with the reality of Hunan power grid,
this paper sum up experience and lessons of
Brazilian blackout.
Keywords—Brazil power grid, blackout, defense line
of power grid, accident analysis
I. INTRODUCTION
At the moment of local time in Brazil, March 21, 2018 at
15:48, a power outage happens in Brazil which lead to the
north and northeast of Brazil grid are separated from the
main grid. Fourteen states of northern and northeastern
Brazil have widespread blackout and loss load about
21735MW which count 27 percent of National Integrated
System(SIN). Fourteen states in the north and northeast of
Brazil were severely affected, with 2,049 cities accounting
for 93% (2,204 cities in total). The south, south-east and
midwest of Brazil have been affected, including Sao Paulo,
Rio DE janeiro, Minas, Barana, Santa catarina, Goias, Mato
grosso, South mato grosso and the federal autonomous
region, a total of nine states.
The blackout caused huge economic loss and serious
social impact. At the same time, some problems of Brazilian
power grid are exposed. This paper briefly introduces the
general situation of the Brazilian power grid and analyzes the
development process and main reasons of the blackout. At
the end, this paper analyzes and concludes the experience
and lessons of the Brazil blackout which can be used as
reference for the operation and development of Hunan power
grid.
II. POWER GRID OVERVIEW
A. The overview of Brazilian power grid and the review of
historical blackout
The power grid of Brazil is divided into northwest power
grid, north power grid, midwest power grid and southeast
power grid. The southeast power grid of Brazil, including
economic centers like Rio DE janeiro and Sao Paulo, is the
load center of Brazilian power grid, and its load accounts for
more than 50% of the whole power grid.
Brazil's National Integrated System(SIN) includes: the
Itaipu hydropower station-Sao Paulo's delivery project; the
Tucurui power plant delivery project, which connects the
northern and northeastern power grids, and the north-south
grid interconnection system.
Brazil has suffered several large-scale power outages in
the last decade. At 22:13 on November 10, 2009, the power
transmission line of the Itaipu hydroelectric power plant in
Brazil has fault trip, resulting in power failure in four major
cities in the southeast, including Sao Paulo, Rio DE Janeiro
and other continents [1].
At 0:8 on February 4, 2011, the malfunction of relay
underreaching protection of circuit breaker which installed
between the circuit and the bus of the fault substation
luizgonzaga-sobradinho lead to the northeast power grid
separated from the north power grid and the national power
grid of Brazil, and the isolated operation of the northeast
power grid [2]. At 15:50 on September 13, 2016, due to the
fault tripping of 600kV Madeira I dc project's two poles
successively, the National Integrated Systems’s power failure
occurred within a small scope, and the power grid was
basically restored to normal at 18:31 of the same day [3].
B. Belo Monte phase I 800kV HVDC project
Belo Monte Hydropower Station, which located in the
north of Brazil with installed capacity of 11000MW,
transmits power to Estreito converter station, which located
in the south of Brazil through Xingu converter station and
800kV dc line of Belo Monte phase I, with rated power of
4000MW. At the same time, the northern and northeastern
parts of Brazil, the northern and southern parts, and the
northeastern and southeastern parts of Brazil each are
connected by 500kV ac liaison line.
In order to meet the requirements of power delivery of
Belo Monte Hydropower Station, ANEEL of Brazil hopes
that the first-phase HVDC project (800kV) of Belo Monte
will be put into operation in advance. After the negotiation
with the project company, ANEEL has proposed a phased
bus-bar operation plan for Xingu converter station. The main
wiring diagram of Xingu converter station is shown in Fig.1.
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Manaus
Macapá
Jurupari
SE Xingu
B
F
SA
F
F
Section switch
9522
A
Belo Monte
UHE
Belo Monte
Tucurui
UHE
Tucurui
Imperatriz
Marabá
Sistema NE
Colinas
Sistema NE
Interligação Norte-Sul
Estreito
Sistema S/SE-CO
Fig. 1. Main wiring diagram of Xingu converter station
The phased bus-bar operation plan are as follows.
Stage 1: 500kV B bus operates without circuit breaker to
ensure the debugging and operation of bipolar DC.
Stage2: 500kV A bus with circuit breaker is put into
operation, and 500kV B bus is shut down and relevant
equipment is installed.
Stage 3: 500kV B bus operates with circuit breaker.
Before the blackout, Xingu converter station ac bus-bar is
in the second stage of the construction process. The 500kV A
bus adopts the operation mode with circuit breaker, and the
over current protection’s preset value of section switch 9522
is set to 4000A.
III. THE OVERVIEW OF BLACKOUT AND THE ANALYSIS OF
CAUSES
A. The process of the accident
According to the accident investigation report issued by
Brazilian Power Grid Dispatching Center (ONS) on June 4,
2018, the development process of the blackout is as follows.
1) The over-current protection of the section switch act
which lead to a DC bipolar block of Belo Monte first-phase
HVDC project.
Before 15:48 p.m., the transmission power of the DC line
was increased to 4000MW while the current was 4400A. The
section switch of A bus operate correctly because of the
over-load protection. As a result, the converter station’s
500kV bus voltage drops and the Belo Monte first-phase
HVDC bipolar was blocked.
2) The security device did not operate in time, and the
power system splitting into isolated grid.
After the DC line bipolar blocking, the power flow
transfer to the AC line due to the failure of SEP that the
hydropower units of the Belo Monte Hydropower Station
were not removed in time. As a result, the important links
connecting the north, northeast and south jumped off in
about three seconds after the accident. And the northern
power grid and northeastern power are Split from the
southern main grid. About 15:48:06,The Brazilian grid forms
three main isolated grids: the northern grids, the northeastern
grids and the southern grids(including the southeastern and
central grids).
3) Each isolated network operates independently. The
isolated networks in the East and northeast collapsed.
B. Analysis of Accident Causes
1) The reason of the over-current protection action of the
Xingu converter station’s section switch and the bipolar
block of Belo Monte first-phase HVDC is the error of the
over-current protection’s set value of the section switch 9522.
The ONS stated in its subsequent statement that it was
not clear to them that the over-current protection’s set value
of the section switch 9522 was 4000A. Therefore, they gave
instructions that DC should operate at rated power of
4000MW before the accident. As a result, the AC current
reaches 4400A which was exceeding the set value of 9522
over-current protection.
2) Because the SEP does not consider the extreme
situation of voltage loss of both 500 kV AC buses and the
voltage loss of single bus during single bus operation
transition period.
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a)After the large-scale power transfer from DC line to the
AC channel in the Northern Power grid, many lines tripped.
After the DC bipolar blocking, the SEP receives the cutoff signal, that cutting six units of Belo Monte Hydropower
Station, from Siemens DC control and protection system.
However, the SEP was still judged invalid, so the cut-off
signal was not sent to the Belo Monte Hydropower Station.
As a result, the removal of Belo Monte Hydropower
Station’s units is delayed and the accident was further
expanded.
When the northern power grid is isolated, due to the
unbalance between generation and load, the system
frequency rises to 71.69Hz (power frequency 60Hz), and the
generator unit is cut off by protection. At 15:49:21, the
northern isolated network system collapsed, and the
frequency fluctuation of the northern system is shown in Fig.
2.The total lost load of the northern power grid is 5750 MW,
accounting for 93% of the load before the fault.
3) During the operation of the isolated network, the loss
load of the Northern and Northeastern Power Grids is
relatively serious. The power system remains stable while the
Southern Power Grid’s under-frequency load shedding act.
80
Sao Luiz
70
Manaus
60
f/Hz
Macapa
Belén
50
18:50:53.333
18:50:45.000
18:50:36.666
18:50:28.333
18:50:20.000
18:50:11.666
18:50:03.333
18:49:55.000
18:49:46.666
18:49:38.333
18:49:30.000
18:49:21.666
18:49:13.333
18:49:05.000
18:48:56.666
18:48:48.333
18:48:40.000
18:48:31.666
18:48:23.333
18:48:15.000
18:48:06.666
18:47:58.333
18:47:50.000
18:47:41.666
18:47:33.333
18:47:25.000
18:47:16.666
18:47:08.333
30
18:47:00.000
40
Time
Fig. 2. Frequency Fluctuation in Northern power System
b) After the accident, the transfer of power flow resulted
in the power system separation of the Northeast Power Grid
to the North and South Power Grids from Pres. Dutra
Substation, Ribeiro Gonalves Substation and Bom Jesus Da
Section switch
9552 trip
Lapa Substation. The frequency of isolated network dropped
to 57.3Hz, and the frequency fluctuation in Northeast power
system is shown in Fig.3.
60Hz
58.5Hz
The thermal power plants
removed from the power grid
57
Frequency Restored
after load shedding
Two units of Paulo Afonso
Hydropower Plant were cut off
successively
52
f/Hz
The frequency is less than 58.5Hz
and maintains for more than 10s.
The relay protection equipment act.
47
Fortaleza
18:48:49.166
18:48:48.333
18:48:47.500
18:48:46.666
18:48:45.833
18:48:45.000
18:48:44.166
18:48:43.333
18:48:42.500
18:48:41.666
18:48:40.833
18:48:40.000
18:48:39.166
18:48:38.333
18:48:37.500
18:48:36.666
18:48:35.833
18:48:35.000
18:48:34.166
18:48:33.333
18:48:32.500
18:48:31.666
18:48:30.833
18:48:30.000
18:48:29.166
18:48:28.333
18:48:27.500
18:48:26.666
18:48:25.833
18:48:25.000
18:48:24.166
18:48:23.333
18:48:22.500
18:48:21.666
18:48:20.000
18:48:19.166
18:48:18.333
18:48:17.500
18:48:16.666
18:48:15.833
18:48:15.000
18:48:14.166
18:48:13.333
18:48:12.500
18:48:11.666
18:48:10.833
18:48:10.000
18:48:09.166
18:48:08.333
18:48:07.500
18:48:06.666
18:48:05.833
18:48:05.000
18:48:04.166
18:48:03.333
18:48:02.500
18:48:01.666
18:48:00.833
18:48:20.833
Recife
42
Time
Fig. 3. Frequency fluctuation in Northeast power system
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and maintains for more than 10s. As a result, the relay
protection equipment act, and the thermal power plants is
removed from the power grid. The system frequency drops
sharply, and the Northeast isolated network system collapses.
Before isolated network formed in the Northeastern
Power grid, under frequency load shedding for 5 rounds with
a total load shedding of 1000MW was performed. After the
under frequency load shedding operation, the isolated
network frequency of northeast power grid was restored to
60Hz, and the system maintained short-term stability. At
15:48:20 and 15:48:25, two units of Paulo Afonso
Hydropower Plant were cut off successively because of the
relay protection equipment. The isolated network frequency
dropped again from about 60 Hz to less than 58.5 Hz. As the
Northeast power grid didn’t has further action in under
frequency load shedding, the frequency is less than 58.5Hz
c)After the accident occurred, the southern power system
formed an isolated network at about 15:48:06. At around
15:48:08, the frequency of southern power system dropped
to 58.44 Hz (power frequency 60 Hz). After the 3665MW
load was removed from the system by under frequency load
shedding, the system gradually restored to stability. The
frequency fluctuation of the system in the southern power
system is shown in Fig.4.
60.15522
Brasilia
59.65522
Belo
Horizonte
Curitiba
f/Hz
Campo Grande
59.15522
Sao Carlos
Florianopolis
Campinas
58.65522
18:48:42.500
18:48:41.666
18:48:40.833
18:48:40.000
18:48:39.166
18:48:38.333
18:48:37.500
18:48:36.666
18:48:35.833
18:48:35.000
18:48:34.166
18:48:33.333
18:48:32.500
18:48:31.666
18:48:30.833
18:48:30.000
18:48:29.166
18:48:28.333
18:48:27.500
18:48:26.666
18:48:25.833
18:48:25.000
18:48:24.166
18:48:23.333
18:48:22.500
18:48:21.666
18:48:20.000
18:48:19.166
18:48:18.333
18:48:17.500
18:48:16.666
18:48:15.833
18:48:15.000
18:48:14.166
18:48:13.333
18:48:12.500
18:48:11.666
18:48:10.833
18:48:10.000
18:48:09.166
18:48:08.333
18:48:07.500
18:48:06.666
18:48:05.833
18:48:05.000
18:48:04.166
18:48:03.333
18:48:02.500
58.15522
18:48:20.833
58.44Hz
Time
Fig. 4. Frequency fluctuations in the southern, southeastern and central Western Power system
IV. THE ENLIGHTENMENT OF THE BLACKOUT TO HUNAN
POWER GRID
Brazil's 3.21 blackout was caused by the incorrect set
value of the section switch’s relay protection. The incorrect
action of stability control equipment after the blocking of the
DC system led to the further expansion of the blackout,
which led to the tripping operation of the regional grid tie
lines and the power system separation.
A. Attention on the coordination of relay protection and
operation mode
According to the 3.21 Brazilian blackout briefing, the
tripping of section switch is not because of the incorrect set
value. The real reason is that the Brazilian Power Grid
Dispatching Center(ONS) is not clear about the set value of
the section switch and the actual wiring, but still issued an
order to transmit at the rated power of 4000MW which
resulting in the trip of the section switch.
As the first defense line of power grid, the relay
protection devices, which cooperate with the operation mode,
is the key to ensure the safety and stability of the power grid.
According to the domestic industry habits, to ensure the relay
protection equipment do not work, the set value should take
full account of the load level of the line. And the set value is
issued or filed by the dispatching department. There is no
case that the dispatching department is not clear about the
actual set value. Therefore, the blackout in Brazil exposed
the problem of information exchange and sharing between
the Brazilian power grid dispatching center and converter
station.
In addition, there is high power transmission on the
AC/DC channel in Brazilian power grid. The carrying
capacity when DC blocking and stability control equipment
did not cutting of the units wasn’t take into consideration.
Therefore, when bipolar blockade occurs in Belo Monte
first-phase (±800 kV) HVDC transmission project, the AC
line trips successively.
For Hunan power grid, Qishao DC power transmission
has reached a maximum of 4500MW. It is necessary to pay
more attention to the safety of the power system when power
on DC lines transfer to AC channel after DC block.
B. Development of Safety and Stability Device
Configuration and Strategies
From the development of blackouts, stability control
equipment of Xingu converter station did not cut the units of
Belo Monte Hydropower Station, which is the root of
accident expanding. In the actual fault, the DC control and
protection system issued the cut-off instructions, but the
stability control equipment decided that the cut-off
instructions were invalid for the reason that the stability
control equipment did not allocation the action strategy when
both 500kV bus lose voltage or single bus, during the
transitional period, lose voltage.
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Shaoshan converter station of Hunan power grid is the
receiving station of Qishao DC. It is suggested that the
configuration and strategy of stability control equipment of
Shaoshan converter station should be further improved,
especially in special working conditions which may occur
during the transition period of construction. And the stability
control equipment should be tested before it connect to grid.
It should be ensured that the stability control equipment can
cut load correctly in normal operation, maintenance
operation and transition period.
C. Attention on primary frequency regulation
Characteristics of Units
During the blackout in Brazil, as the receiving end of the
Belo Monte first-phase (±800 kV) DC project, the southern
power grid’s frequency dropped to 54.88 Hz after the
accident. The frequency of the power system recovery takes
about 17 seconds. The recovery time of the receiving-end
grid’s frequency is closely related to the operating speed of
the unit's primary frequency regulation characteristic.
Similarly, to ensure that the primary frequency regulation
of units in Hunan province can act correctly in time in case
of various blocking accidents and holdover frequency
stability. Hunan power grid, as the receiving end of Qishao
DC, is suggested to strengthen the technical supervision of
primary frequency regulation parameters.
D. Improving the under-frequency load shedding
configuration
After expansion of effect of the blackout in Brazil, the
strategy of under frequency load shedding is insufficient
after the operation of the isolated network in the
Northeastern Power grid. As a result, two units in the Paulo
Afonso hydropower plant overload trip out because of the
over load. And the frequency of the system cannot be
restored, which eventually leads to system collapse. From
this point of view, the power grid should be equipped with
enough sufficient under frequency load shedding. And its
configuration should cooperate with the system separation
scheme to ensure the security of the system or the isolated
network.
Fourteen regional power grids in Hunan power grid are
equipped with basic I-V load shedding rounds, which
divided by equal capacity, with a total load shedding of
7270MW. In addition to the Xiang xi, Huaihua and
Zhangjiajie power grids, the other regional power grids are
equipped with special three rounds of under frequency load
shedding, which divided by equal capacity, with load
shedding capacity of about 1620MW. Hunan power grid’s
under frequency load shedding configuration uses the
average maximum load of each region as the base, and the
under frequency load shedding allocates about 40% of the
total load.
With the development of society and economy, the
electrical load of Hunan power grid has reached new heights.
The allocation of under frequency load shedding
configuration in Hunan power grid should match the
electrical load of the grid. It ensures that the load can be
effectively reduced under the extremely arduous condition of
low frequency. And it also ensures the safety of the power
grid, and avoids large-scale blackouts.
CONCLUSION
In this paper, the background, cause and development
process of Brazilian blackout are introduced in detail. And
the causes of occurrence and expansion of the accident are
analyzed based on the introduction of Brazilian blackout.
According to the problems in each link of accident
development, the possible operation risks of Hunan power
grid are analyzed.
Hunan power grid should attach importance to relay
protection’s set value management, and carry out safety and
stability device configuration and strategy combing to set
effective fault response measures. Meanwhile the technical
supervision of primary frequency modulation parameters of
important units should be carried out, and the underfrequency load shedding configuration of Hunan power grid
should be improved.
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