ISBN 978-0-620-44584-9
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
SIDE EFFECTS OF CURRENT-LIMITING REACTORS IN
TRANSMISSION LINE
Yang Pengcheng, Chen Shuiming*, Xu Wei, Bian Xiao, Wang Wei
State Key Lab of Control and Simulation of Power Systems and Generation Equipments
Tsinghua University, Beijing 100084, China
*Email: chensm@tsinghua.edu.cn
Abstract: Air-cored Current-Limiting Reactor (CLR) is widely used to limit the magnitude of
fault current in power systems, while at the same time the application of CLR also brings some
problems. This paper deals with the side effects of CLR on three types of transient overvoltages in
the power transmission line, namely, transient recovery voltage (TRV), switching overvoltage
(SOV) and temporary overvoltage (TOV). Various simulations are carried out with
PSCAD/EMTDC. Researches show that TRV caused by single-phase short circuit fault exceeds
the limit in China. For this problem, parallel capacitors can be used to restrain TRV, and the
method of choosing its location and capacity is also discussed in this paper. The simulation results
indicate that with the increase of CLR impedance, the magnitude of SOV and TOV also goes up or
even exceeds the limit. Equivalent Circuit Method is developed to evaluate the influence of CLR
on SOV. In general, CLR will cause the TRV, SOV and TOV rise. Simulations are strongly
recommended before CLR be used to ensure the overvoltage of transmission line below the limit.
1
the voltage drop, the joule losses and the high magnetic
INTRODUCTION
fluxes (higher distances/clearances required). On the
As the power system developing, the short-circuit
other hand, despite these disadvantages, their effects
current levels are also increasing rapidly. In some
could be economically compensated when avoiding
substations, the short-circuit current levels have been
equipment substitution.
close to or even exceeded the capacity of circuit
breakers. Decreasing the short-circuit current levels can
It can also be demonstrated that the presence of a
not only prevent important equipments from being
lumped inductance in an electric circuit could lead to an
broken down by large fault current, but also reduce
increase in the severity of the transient recovery voltage
electromagnetic interference caused by fault current.
(TRV) across the circuit breaker (CB) contacts,
The most common solutions to high fault current levels
associated with the interruption of the circuit current [1].
are[1]: up-rating of switchgear and other equipment;
The switching overvoltage (SOV) and temporary
splitting the grid and introducing higher voltage
overvoltage (TOV) will also increase because of the
connections (AC or DC); introducing higher impedance
lumped inductance. In this paper, various simulations
transformers and series reactors; and using complex
are carried out with PSCAD/EMTDC, the results of
strategies like sequential network tripping. Nevertheless,
which are shown in the following sections. The CLR
these alternatives may create other problems such as
discussed in this paper is 0.025H.
loss of power system security and reliability, high costs,
2
and increase of power losses. Up to now, the usage of
air-core current-limiting reactor (CLR) is an adopted
SIDE EFFECTS OF CLR ON TRV
When CLR is inserted into the circuit, for instance, to
solution. The applications of CLR in Brazil [1] and
limit the short circuit current, the rate of rise of the
Canada [2] showed that CLR had good effects on
transient recovery voltage tends to drastically increase
restraining fault current.
because of its very large surge impedance (at least
several thousands of Ohms). Fortunately, however,
The guidance factors for CLR dimensioning, which
installing a suitable capacitor across the reactor may
could even make the CLR application unfeasible were
Pg. 1
Paper G-41
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
easily solve this problem. In some cases it might be
2)
necessary to install capacitors from each side of the
of line, the amplitude as well as steepness of TRV at
reactor to ground. In any case, usually an in-depth
Huangdu exceeds the limit and the steepness of TRV at
computer analysis must be performed to make sure the
Sijing exceeds the limit.
While single phase fault takes place in the middle
circuit breaker characteristics are not exceeded.
3)
While single phase fault takes place near Sijing
Based on 500kV Sijing-Huangdu transmission line
substation, the steepness of TRV at both Huangdu and
where CLR was used for the first time in China [3],
Sijing exceeds the limit.
TRV and the suitable restraining measures are presented
TRV while single phase fault takes place near Sijing
in this section.
Substation are shown in Figure 2
The equivalent network and the parameters of
transmission lines are shown in Figure 1 and Table 1.
(a)
Fig 1: Equivalent Network
Table 1: Transmission Line Parameters of Equivalence
Power Network
Line Names
Wires
Length
Shipai～Huangdu
Double-circuit 4×400
38 km
Huangdu～Sijing
Double-circuit 4×400
23 km
Sijing～Nanqiao
Double-circuit 4×400
26 km
Huxi～Sijing
Double-circuit 6×630
25 km
As defined in GB 1984－2003 of China, the standard
(b)
value of TRV across the circuit breaker is shown in
Fig 2: TRV while Fault near Sijing Substation (a) TRV
Table 2.
2.1
at Huangdu (b) TRV at Sijing (The Line in Red is the
Limit of TRV)
TRV Caused by Single Phase Short-circuit
Lots of simulations have been done to calculate TRV at
2.2
substations when single phase fault taken place. The
As mentioned in the beginning of this section, parallel
results show that:
1)
Measures to Restrain TRV
capacitors can be used to restrain TRV. In the project
design, 60 nF capacitors are installed at Sijing
While single phase fault takes place near Huangdu
substation. TRV while single phase fault near Sijing
substation, the amplitude of TRV at Huangdu exceeds
substation are shown below.
the limit and the steepness of TRV at Sijing exceeds the
limit.
Pg. 2
Paper G-41
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
Table 2: Standard Value of TRV with 4-Parameters in 500kV
Rated voltage
First off
Amplitude
First Reference
Time1
Amplitude of
Time2
Coefficient
Factor
Voltage (kV)
(μs)
TRV (kV)
(μs)
Outlet Fault
1.3
1.4
438
219
817
876
Short Line Fault
1
1.4
337
168
629
672
Test Method
(kV)
550
Figure 3 demonstrate that capacitors installed at Sijing
have some effects on restraining TRV at Sijing. While
at Huangdu, there is little effect. TRV at both sides of
transmission line still exceeds the limit. In order to
suppress TRV to the limit, much larger capacitors
should be installed at both sides of the line.
900
None
L+C
L
800
700
600
(a)
kV
500
400
300
200
100
0
-100
0.3158
0.316
0.3162
0.3164
0.3166
s
0.3168
0.317
0.3172
0.3174
(a)
900
None
L+C
L
800
700
600
(b)
kV
500
400
Fig 4: TRV While Fault near Sijing Substation when
0.8μF capacitors installed (a) TRV at Huangdu (b) TRV
300
200
at Sijing (The Line in Red is the Limit of TRV)
100
0
-100
0.316
0.3162
0.3164
0.3166
0.3168
s
0.317
0.3172
0.3174
3
0.3176
EFFECTS OF CLR ON SWITCHING
OVERVOLTAGE
(b)
Fig 3: TRV while Fault near Sijing Substation when 60
nF capacitors installed (a) TRV at Huangdu (b) TRV at
With CLR installed on the transmission line, theoretical
Sijing
at the same time. Taking switching overvoltage of three
(Red-Limit;
Blue-no
CLI
and
analysis shows that switching overvoltage will increase
Capacitor;
phases energizing line with no load for example [4],
Green-with CLI; Black-with CLI and capacitor)
U c = U cm [− cos(ωt + ϕ ) +
Researches suggest that 1 μF and 0.8 μF parallel
capacitors installed at Huangdu and Sijing substation
2
ω 
2
2
−δ t
  sin ϕ + cos ϕ e cos(ω0t + θ )]
ω
 0
respectively is a good choice. In this case, the TRV at
both sides of line meets the limit as shown in figure 4.
Pg. 3
(1)
Paper G-41
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
Where UC is the voltage at the terminal of transmission
line, and ϕ 0 is the phase angle when energizing, R L
For that switching overvoltage depends on the phase,
and C are equivalent resistance inductance and capacitor
maximum 98% statistical overvoltage.
Monte Carlo based simulations were made to get the
of transmission line.
Table
φ = φ0 − arctan
ω0 =
4:
Three
Phase
Energizing
Switching
Overvoltage of 750kV transmission line
1
ωC , tan θ = ω tan φ , δ = R ,
R
ω0
2L
ωL −
0km
80km
160 km
240 km
320 km
400 km
1.49p.u
1.61p.u
1.68p.u
1.72p.u
1.76p.u
1.75p.u
1.52p.u
1.64p.u
1.70p.u
1.74p.u
1.79p.u
1.75p.u
No
1
−δ 2
LC
CLR
For the sake of simplicity, it is assumed that R is so
With
small that it could be ignored; as a result attenuation
coefficient is 0. In the case that ϕ 0 is 90 degree, the
CLR
following can be derived
U cm =
Table 5: Single Phase Reclosing Switching Overvoltage
of 750kV transmission line
1
Uc
ω2
1− 2
ω0
(2)
0km
80km
160 km
240 km
320 km
400 km
1.25p.u
1.31p.u
1.34p.u
1.34p.u
1.32p.u
1.29p.u
1.24p.u
1.33p.u
1.36p.u
1.36p.u
1.34p.u
1.29p.u
No
CLR
ω0 =
1
(3)
LC
With
CLR
−b ± b2 − 4ac
will
2a
rise as far as L increases. Results of related simulations
These results show that adding CLR to the transmission
are consistent with the theory. These simulations are
consistent with the theory above. As the impedance of
based on a real-life 750kV power transmission line, the
CLR is small compared to that of the transmission line,
parameters of which are shown in Table 3
the rising rates of switching overvoltage are not
As shown above, ω0 and U cm
line indeed increases the switching overvoltage which
obviously. Actually, switching overvoltage of three
phases energizing line with no load and single phase
Table 3: Parameters of 750kV Transmission Line
reclosing rise by 1.74% and 1.69% separately. The most
Line Names
Wires
Length
severe switching overvoltage is 1.79p.u., lower than the
Yinchuan~Lanzhou
6×400
400 km
limit value in China.
Table 6: Switching Overvoltage while Different CLR
CLR(Ω)
0 km
80km
160 km
240 km
320 km
400 km
7.85
1.52 p.u.
1.64 p.u.
1.70 p.u.
1.74 p.u.
1.79 p.u.
1.75 p.u.
Three Phase
20
1.55 p.u.
1.66 p.u.
1.73 p.u.
1.76 p.u.
1.82 p.u.
1.76 p.u.
Energizing
40
1.60 p.u.
1.70 p.u.
1.76 p.u.
1.81 p.u.
1.86 p.u.
1.76 p.u.
60
1.64 p.u.
1.76 p.u.
1.85 p.u.
1.89 p.u.
1.90 p.u.
1.77 p.u.
7.85
1.24 p.u.
1.33 p.u.
1.36 p.u.
1.36 p.u.
1.34 p.u.
1.29 p.u.
Single Phase
20
1.23 p.u.
1.37 p.u.
1.38 p.u.
1.40 p.u.
1.39 p.u.
1.28 p.u.
Reclosing
40
1.23 p.u.
1.42 p.u.
1.42 p.u.
1.47 p.u.
1.47 p.u.
1.27 p.u.
60
1.24 p.u.
1.44 p.u.
1.44 p.u.
1.49 p.u.
1.48 p.u.
1.29 p.u.
Pg. 4
Paper G-41
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
Further more, effects of other CLR are also researched.
( L0 * l + LC )* C0 * l = (l + le ) 2 * L0 C0
Based on Equation 3, as the impedance of CLR
(4)
increases, the overvoltage will rise as well. Effect of
Where l is the length of line; LC is the impedance of
CLR with different impedance is shown in Table 6.
CLR; le is the length of equivalent line for CLR.
As previously stated, it is obvious that installing CLR to
Generally, le is much smaller than l, so the quadratic
transmission
term can be ignored
line
will
increase
the
switching
overvoltage. The up-rate of overvoltage depends on the
le =
impedance of CLR, especially for 3 phase energizing
switching overvlotage. If the impedance of CLR is
greater than 20 Ω, it will exceed the limit (1.8 p.u.).
LC
2L0
(5)
Based on the equation, in the simulations, CLR can be
At the same time, a simple method called Equivalent
substituted by a segment of line whose length is le. As
Circuit Method is developed to estimate the increase of
for the 750kV transmission line studied in this section,
switching overvoltage cause by CLR. As shown in
the inductive reactance of line is 0.2649 Ω/km, so the
Equation 2, the increase depends on ω0. CLR leads to
length of equivalent line is 14.82km. The simulations’
the total impedance of line rises, which is equivalent to
results of Equivalent Circuit Method are shown in Table
prolong the transmission line. Correspondingly, CLR
7.
can be considered as line for the sake of simplicity. It is
As shown below, the error of Equivalent Circuit Method
assumed that ω is the oscillation frequency of line
is 0.68% and 1.46% for switching overvoltage of 3
with CLR, and ω ' is the oscillation frequency of
phase energizing and single phase reclosing separately.
equivalent line. ω = ω ' , following equation can be
As the error is small, it is a good choice to estimate the
derived:
switching overvoltage with Equivalent Circuit Method
when CLR is installed.
Table 7: Switching Overvoltage Results with Different Methods
Method
0 km
80km
160 km
240 km
320 km
400 km
Three Phase
With CLR
992 kV
1069 kV
1113 kV
1138 kV
1167 kV
1145 kV
Energizing
Equivalent Circuit
954 kV
1056 kV
1114 kV
1145 kV
1159 kV
1146 kV
Single Phase
With CLR
809 kV
871 kV
885 kV
890 kV
877 kV
839 kV
Reclosing
Equivalent Circuit
826 kV
890 kV
903 kV
892 kV
902 kV
860 kV
Table 8: Power Frequency Overvoltage of 750kV Transmission Line
Method
0 km
80km
160 km
240 km
320 km
400 km
With CLR
1.11 p.u.
1.15 p.u.
1.18 p.u.
1.21 p.u.
1.22 p.u.
1.23 p.u.
No CLR
1.10 p.u.
1.13 p.u.
1.16 p.u.
1.19 p.u.
1.20 p.u.
1.21 p.u.
With CLR
1.04 p.u.
1.16 p.u.
1.20 p.u.
1.20 p.u.
1.14 p.u.
1.04 p.u.
No CLR
1.05 p.u.
1.16 p.u.
1.20 p.u.
1.20 p.u.
1.14 p.u.
1.04 p.u.
With CLR
1.11 p.u.
1.16 p.u.
1.19 p.u.
1.22 p.u.
1.24 p.u.
1.24 p.u.
No CLR
1.13 p.u.
1.18 p.u.
1.22 p.u.
1.25 p.u.
1.27 p.u.
1.27 p.u.
Power Frequency
Single Phase Fault
Load Rejection
Pg. 5
Paper G-41
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
4
60 nF capacitor used in the original plan can not restrain
SIDE EFFECTS OF CLR ON TEMPORARY
TRV to the limit perfectly. Researches show 1 μF and
OVERVOLTAGE
0.8 μF parallel capacitors installed at each end of line
CLR will lead to temporary overvoltage rising as well.
respectively can restrain TRV to the limit. Unfortunately,
As for unload lossless transmission line, the ratio of
these capacitors are too expensive for real project. Thus,
voltage at terminal to voltage at head end is [4]
further researches are needed to find another proper way
U&
1
K12 = 2 =
&
U1 cos α l X s sin α l
−
ZC
to solve this problem.
(6)
For switching overvoltage and temporary overvoltage,
installing CLR will also lead to a rise of these
overvoltages except for single phase fault overvoltage.
Where α is phase-shift coefficient, l is the length of line,
Researches show that as far as the impedance of CLR
ZC is line impedance and Xs is the impedance of CLR.
increases, the overvoltage goes up. Equivalent Circuit
α = ω L0C0 , Z c = L0 C0
Method introduced in this paper can be used to estimate
the switching overvoltage while CLR installed.
It is obviously that the power frequency overvoltage will
Regardless of TRV or switching overvoltage or
rise when CLR installed. In order to determine whether
temporary overvlotage, CLR will lead to an increase. As
temporary overvoltage will exceed the limit, related
a result, simulations are strongly recommended before
simulations are made. The line parameters are the same
CLR be used to ensure the overvoltage of transmission
to those in Section 3 which is shown in Table 3.
line below the limit
According to Table 8, following conclusions can be
6
drawn:
1)
CLR will lead to power frequency overvoltage and
load
rejection
overvoltage
increase.
[1]
The
current
limiting
limitation,
There is little effect of CLR on single phase
reactors
International
for
short
Power
circuit
Systems
Transients ( IPST’ 05) . Montreal, Canada, 2005.
grounding fault overvoltage.
[2]
3)
J. Amon F., P. C. Fernandez, E. H. Rose, et al,
Brazilian successful experience in the usage of
overvoltage at the terminal is more severe.
2)
REFERENCES
Terrance A. Bellei, Ernst H. Camm, Gene
When CLR installed, the most severe temporary
Ransom. Current-Limiting Inductors used in
overvoltage is 1.27 p.u. which is close to the limit
Capacitor Bank Applications and Their Impact on
(1.3 p.u.)
Fault Current Interruption. Proceedings of the
IEEE Power Engineering Society Transmission
5
CONCLUSIONS
and Distribution Conference, v 1, 2001: 603-608
[3]
Installing CLR could decrease the fault current levels,
Chen Shuiming, Xu Wei, Wang Zhenxing, et al.
but other problems will be caused at the same time.
Effects of 500 kV Current-Limiting Inductors on
Overvoltage of the transmission line will be close to or
Transient
even exceed the limit. So attention should be paid on the
Countermeasures. North China Electric Power.
level of overvoltage before CLR being installed.
2008,5(1):11~15(in Chinese)
[4]
For TRV across the CB, CLR will lead the amplitude and
Zhang Weibo,
Over-voltage
steepness of TRV exceeding the limit. Installing parallel
Recovery
Voltage
He Jinliang,
Protection
and
Its
Gao Yuming.
and
Insulation
Coordination [M]. Beijing: Tsinghua University
capacitor is a good choice to restrain TRV. As to the
Press, 2002. (in Chinese)
transmission line where CLR is installed first in China,
Pg. 6
Paper G-41