B4-1089
AORC Technical meeting 2014
http : //www.cigre.org
130MVA-STATCOM Installation for Transient Stability Improvement
Y. Matsushita, S. Iwasaki, T. Imanishi
The Kansai Electric Power Co., Inc.
Japan
K. Masaki, F. Nakamura
Mitsubishi Electric Corp.
Japan
J. Ieda
TMEIC
Japan
SUMMARY
KANSAI (The Kansai Electric Power Co., Inc.) transmits electricity generated by hydroelectric power
stations through long-distance 154kV transmission line. There are problems that the whole of potential
power is unable to be supplied under heavy load conditions and that a system fault outside of the
154kV line may cause the loss of synchronism of generators. Therefore KANSAI has installed a new
STATCOM (STATic synchronous COMpensator) with transient stability improving control to solve
these problems.
The STATCOM is a parallel system of 3-stage-converter (78MVA GCT (Gate Commutated Turn-off
thyristor) -STATCOM) and 2-stage-converter (52MVA GCT-STATCOM). Each converter is
connected to 154kV bus through multi-stage transformers. The STATCOM system is equivalent of
130MVA-STATCOM. The STATCOM control scheme is configured by AVR (Automatic Voltage
Regulator) control, PSS (Power System Stabilizer) control, and Q (reactive power) bias control to
improve the damping force and the synchronizing power of the system. In addition, for improving
transient stability, the STATCOM coordinates the AVR and PSS depending on the state of a system
phenomenon at the system fault.
We performed eigenvalue analysis and transient stability analysis to check the system design.
Eigenvalue analysis verified that the STATCOM improved the steady-state stability and had
redundancy to it. Transient stability analysis verified that the STATCOM prevented
generators from losing synchronism.
We performed real-time simulator test to confirm the performance of the STATCOM during a system
fault because it is difficult to cause actually a system fault at the hydroelectric power system.
We simulated the power system in detail by analog type real-time power system simulator and
connected the simulator with STATCOM miniature model, actual control device and multi-stage
transformer model. The test confirmed that the STATCOM operated properly at various faults.
After installing actual STATCOM in Inuyama Switching Station, we conducted performance tests and
field tests. It is confirmed that STATCOM enhanced the steady-state stability of the hydroelectric
power system and increases TTC (Total Transfer Capability) to maximum flow.
KEYWORDS
STATCOM - Transient Stability - Steady State Stability - GCT thyristor
Masaki.Kenji@db.MitsubishiElectric.co.jp
1. Introduction
It tends to install inexpensive and efficient FACTS devices as a countermeasure against various
problems in power system. As restructuring of transmission system has been performed in
consideration of reliability and economy recently, requirement for STATCOM has been becoming
also more demanding such as improvement of transient stability or prevention of the loss of
synchronism [1].
Since KANSAI transmits electricity generated by hydroelectric power generation through longdistance 154kV transmission line, there is a problem that the whole of potential power is unable to be
supplied under heavy load conditions. Moreover there is a problem that a system fault outside of the
154kV line may cause the loss of synchronism of generators. Therefore KANSAI has installed a new
STATCOM with transient stability improving control to solve these problems.
2. 130MVA-STATCOM
(1) Purpose
Figure 1 shows the hydroelectric power system with 154kV long-distance transmission line. Power
flow from the group of generators is supplied to C-S/S through Inuyama-SW/S and B-S/S via 154kV
long-distance transmission line. The distance from the group of generators to C-S/S is about 250km.
Therefore, it makes the power system unstable under heavy load condition, and makes full-power
operation of all generators impossible (about 300MW). Moreover, system faults outside of the 154kV
line in Figure 1 may cause loss of synchronism of generators. Then it is necessary to install the new
STATCOM at Inuyama-SW/S which is the electrical median point of the system and improve steadystate stability and transient stability by the STATCOM.
(2) Configuration
Figure 2 shows the system configuration of the 130MVA-STATCOM. Table 1 shows the specification
of 130MVA-STATCOM. The STATCOM is a parallel system of 3-stage-converter (the left-side :
78MVA-STATCOM) and 2-stage-converter (the right-side : 52MVA-STATCOM). Each converter is
connected to 154kV bus through multi-stage transformers. By both STATCOMs running, the
STATCOM system is equivalent of 130MVA-STATCOM. The large capacity 6kV-6kA GCT (Gate
Commutated Turn-off) thyristor in Figure 3, which achieves high reliability, downsizing, and low loss,
is employed for the 3-level converter unit.
(3) Control
The system stability of power system shown in Figure 1 are weak especially under heavy load flow
because of its long-distance transmission line. For improving system stability, it is necessary to
enhance the damping force and the synchronizing power of the system. Therefore the STATCOM
control scheme is configured by AVR (Automatic Voltage Regulator) control, PSS (Power System
Stabilizer) control, and Q (reactive power) bias control as shown in Figure 4. The AVR control
improves the synchronizing power. The PSS control improves the damping force. The Q bias control
reduces transmission loss and improves steady-state stability. In addition, for improving transient
D-P/S
G
C-S/S
Infinite Bus
System
~
B-S/S
G
154kV
Hydro
generators
G
Inuyama SW/S
78MVA
52MVA
F-P/S
J-bus
G
154kV
275kV
300MW
G
H-P/S
G
Fault-A
77kV 3LG
78MVA 52MVA
E-P/S
130MVA STATCOM
Figure 1. Power System diagram
G
G
I-P/S
G-P/S
group
Figure 2. STATCOM configuration
1
Table 1. Specification of 130MVA-STATCOM
Specification of STATCOM System
±130MVA
Capacity
AC grid voltage
154kV
System configuration
2-parallel
±78MVA, ±52MVA
Capacity of each STATCOM
Specification of 78MVA-STATCOM
±78MVA
Capacity
6kV-6kA GCT，1S1P
Power device
3-level full-bridge ×3phase
Inverter circuit
Multiplex transformer
3-stage multiplex
Capacity /stage of converter
26MVA
3846V，2253A
Voltage, Current /stage of converter
±3000V
DC voltage
Specification of 52 MVA-STATCOM
±52MVA
Capacity
6kV-6kA GCT，1S1P
Power device
3-level full-bridge ×3phase
Inverter circuit
Multiplex transformer
2-stage multiplex
Capacity /stage of converter
26MVA
3846V，2253A
Voltage, Current /stage of converter
±3000V
DC voltage
Figure 3. 6kV-6kA GCT thyristor
Transient Stability
Coordination control
Power flow
Bus voltage
Power flow
PSS control
ΔV type
AVR control
Current
control
reference
Q bias control
Steady-State Stability
Figure 4. STATCOM control
stability much more, the STATCOM coordinates the AVR and PSS by adjusting the gains and limiters
of AVR and PSS depending on the state of a system phenomenon at the system fault. This control
scheme can maximize the effect of improving transient stability by the STATCOM and prevent the
loss of synchronism.
Each STATCOM transmits and receives each operating state signals with each other, and shifts to
appropriate operating condition depending on operating state signal of other STATCOM. The output
of Q bias control is shared with each STATCOM as the capacity ratio when both STATCOM is
running. However, if either one halts, the other one bears total output of Q bias control.
We performed eigenvalue analyses to check steady-state stability enhancing effects by the 130MVASTATCOM. Figure 5 shows the eigenvalue of the power system. In this case, all generators run at
rated power and the steady-state stability is the severest. As shown in Figure 5, real part of the
eigenvalue is positive when no STATCOM exists, which means that the power system is unstable.
However, real part of the eigenvalue is negative when the 130MVA-STATCOM exists. Moreover, the
eigenvalue is negative when capacity of STATCOM is 52MVA. These results show that each
STATCOM ensures steady-state stability alone, that is, the STATCOM system has redundancy to
steady-state stability.
Moreover, we performed transient stability analysis to confirm that 130MVA-STATCOM improves
transient stability of the power system and prevent all generators from losing synchronism against any
system faults outside of the 154kV line. The following Fault-A are the severest fault points outside of
the 154kV line in Figure 1. The 130MVA-STATCOM must prevent all generators from losing
synchronism against Fault-A.
・Fault-A : B-S/S 77kV Bus Feeder Line 3LG fault (Fault period : 233ms)
Figure 6 shows a result of transient stability analysis of Fault-A. In this case, transient stability is the
severest because of heavy power flow which all generators output at rated operation, the closest fault
point to 154kV system and the longest duration fault. As shown in Figure 6, generators lose
synchronism at first wave when no STATCOM exists. On the other hand 130MVA-STATCOM
prevents the loss of synchronism using the control scheme described above against the severest FaultA.
2
2.0
1.8
Period [sec]
With
1.6
130MVA-STATCOM
1.4
]
c
e
1.2
s[
With
1.0
d
52MVA-STATCOM
o
rie
0.8
p
Without
STATCOM
0.6
0.4
0.2
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.0
0.1
0.2
0.3
-Damping
[1/sec]
Damping [1/sec]
Figure 5. System study for steady-state stability by
eigenvalue analysis
Figure 6. System study for transient stability
at Fault-A by simulation
3. Real time Simulator Test
We performed real-time simulator test to confirm the performance of the STATCOM during a system
fault because it is difficult to cause actual system fault at the hydroelectric power system. The
hydroelectric power system containing 154kV long-distance transmission line as shown in Figure 1
was simulated in detail by analog type real-time power system simulator. We connected the simulator
with STATCOM miniature model which is composed of the same constitution as the actual system,
actual control device and multi-stage transformer model. This real time simulator test verified
operation of the STATCOM at the time of various system faults.
Figure 7 shows impedance-frequency characteristic of the hydroelectric power system by the real-time
simulator and one by electromagnetic transient analysis. The upper figure is f-z characteristics of
simulator. The lower figure is one of electromagnetic transient analysis model. Both characteristics are
very well matched. These show that the power system is simulated with great accuracy by real-time
simulator.
Figure 8 shows simulator test result of a close-in 3LG fault. Voltage of the STATCOM connection bus
drops to 0pu. The STATCOM detects a voltage drop and performs gate-block (GB) until the fault is
cleared. After the fault is cleared, the STATCOM detects a restoration voltage and performs gate deblock(DEB) immediately. The test confirmed that the STATCOM operates properly at a close-in 3LG
fault.
4. Field Test
After installing actual STATCOM in Inuyama SW/S, we conducted performance tests and field tests.
Figure 9 shows performance test result to verify the the operational mode changing function as one of
performance tests. Before 52MVA-STATCOM is stopped, the 130MVA-STATCOM outputs
Figure 7. Impedance-Frequency characteristics
Figure 8. Simulator test result of a close-in 3LG fault
3
Figure 9. Test result of the mode switching
of the STATCOM control
Figure 10. Test result of transmission capability
10Mvar by Q bias control (78MVA-STATCOM outputs 6Mvar and 52MVA-STATCOM outputs
4Mvar). After 52MVA-STATCOM is stopped, 78MVA-STATCOM performs gate-block (GB)
temporarily and changes from double bundle operational mode to single operational mode. Q bias
control of 78MVA-STATCOM sets command value into 10Mvar. 78MVA-STATCOM performs gate
de-block(DEB) immediately. This test confirmed that the STATCOM operates stably without current
fluctuation of it when changing operational mode.
We also performed a field test which checks that the STATCOM increases TTC of hydroelectric
power system. As in figure 5 in the absence of STATCOM, the power system becomes unstable under
full-power operation of all generators. That is, TTC is less than the maximum flow. In this test, the
STATCOM was operated and the output of the generators was increased gradually. Figure 10 shows
result of the field test under maximum flow. Figure 10-① shows that the power system is stable under
maximum flow by the 130MVA-STATCOM actuating and outputting reactive power by Q bias
control. Additionally, in order to confirm the redundancy for the steady-state stability, 78MVASTATCOM is stopped when both STATCOM operate at the maximum flow. After 78MVASTATCOM is stopped, 52MVA-STATCOM changes operational mode and increases reactive current
output by Q bias control. Figure 10-② shows that even 52MVA-STATCOM solely ensures steadystate stability and increases TTC to maximum flow. Then 78MVA-STATCOM restarts, and 52MVASTATCOM changes operational mode and returns reactive current output to previous value in Figure
10-③. This test confirmed that the STATCOM enhances the steady-state stability of the hydroelectric
power system and increaces TTC to maximum power flow since system voltage, power flow and
output of reactive current of the STATCOM are stable regardless of the operational mode of the
STATCOM.
5. Conclusions
A new STATCOM has been installed for stable power transmission of hydroelectric power. The
STATCOM has the smart effect of transient stability improvement as well as the effect of steady-state
stability improvement. The system stability improvement effected by the STATCOM was confirmed
by simulator test and field test. This STATCOM has started the commercial operation in 2013.
References
[1] S. Mori, "Initiatives perspectives by the power industry towards a low carbon emission society,"
Keynote address of Paris Session CIGRE 2010.
4