The International Symposium on High-Voltage Technique "Höfler's Days", 7–8 November 2013, Portoroz, Slovenia.
1
Transients Caused by Uncontrolled and
Controlled Switching of Circuit Breakers
Ivo Uglešić, Božidar Filipović-Grčić and Srećko Bojić
Abstract—This paper describes transients caused by
uncontrolled and controlled switching of high-voltage circuit
breakers. Inrush currents due to shunt reactor energization were
analyzed. Switching-off, energization and auto-reclosure of
unloaded 400 kV transmission line is presented. Transient
recovery voltage and voltage distribution between breaking
chambers of circuit breaker are investigated. Calculation models
were developed in EMTP-RV software and some field
measurements are presented. Results show that controlled
switching significantly reduces inrush currents and suppresses
switching overvoltages.
Index Terms—circuit breaker, controlled and uncontrolled
switching, shunt reactor, inrush current, no-load 400 kV
transmission line, simulations, measurements.
I. INTRODUCTION
U
NCONTROLLED switching of shunt reactors, shunt
capacitors and transmission lines may cause severe
transients such as high overvoltages or high inrush currents
[1]. Conventional countermeasures such as pre-insertion
resistors, damping reactors or resistors, or arresters are used to
limit the magnitude and effect of the switching transients, after
they have occurred. In addition, system and equipment
insulation may be upgraded to withstand the stresses. These
methods, however, may be inefficient, unreliable or expensive,
and do not treat the root of the problem [2].
Controlled switching is a method for eliminating harmful
transients via time controlled switching operations. Closing or
opening commands to the circuit breaker are delayed in such a
way that switching will occur at the optimum time instant
related to the voltage phase angle. Controlled switching has
become an economical substitute for a closing resistor and is
commonly used to reduce switching surges. The number of
installations using controlled switching has increased rapidly
due to satisfactory service performance since the late 1990s
[3]. Currently, it is often specified for shunt capacitor and
shunt reactor banks because it can provide several economic
benefits such as elimination of closing resistors and extension
of a circuit breaker nozzle and contact maintenance interval. It
also provides various technical benefits such as improved
I. Uglešić and B. Filipović-Grčić are with the University of Zagreb,
Faculty of Electrical Engineering and Computing, Unska 3, 10000 Zagreb,
Croatia (e-mail: ivo.uglesic@fer.hr; bozidar.filipovic-grcic@fer.hr).
S. Bojić is with Energy Institute Inc., Ul. grada Vukovara 37, 10000
Zagreb, Croatia (e-mail: srecko.bojic@ie-zagreb.hr).
power quality and suppression of transients in transmission
and distribution systems [4].
This paper describes switching transients caused by
uncontrolled and controlled switching of circuit breaker.
Switching of shunt reactor and no-load transmission line is
analyzed using EMTP-RV software. Field measurements are
presented and compared with simulation results.
II. TRANSIENTS CAUSED BY SWITCHING OF SHUNT REACTOR
The function of shunt reactors in transmission networks is to
consume the excess reactive power generated by overhead
lines under low-load conditions, and thereby stabilize the
system voltage. They are quite often switched in and out on a
daily basis, following the load situation in the system.
Energization of a shunt reactor may cause inrush currents with
high asymmetry and long time constants. The actual magnitude
of the inrush current is quite dependent on the range of
linearity of the reactor core and on the time instant of circuit
breaker pole operation with respect to the reference signal.
Switching operations at unfavorable instants can cause
currents that may reach high magnitudes and have long time
constants. At shunt reactors with solidly grounded neutral,
unsymmetrical currents cause zero-sequence current flow
which can activate zero-sequence current relays [5].
A. Model Description
The inrush currents due to energization of 150 MVAr shunt
reactor in 110 kV network have been observed. Both
uncontrolled and controlled circuit breaker switching is
simulated. Shunt reactor manufacturer data are shown in Table
I.
TABLE I 150 MVA SHUNT RECTOR DATA
Rated power
Rated frequency
Rated voltage
Rated current
Core type
Total losses (at 110 kV)
Impedance in saturation
Zero sequence impedance
Stationary magnetic flux
Capacitance of winding to
ground
150 MVAr
50 Hz
110 kV
787 A
Five limb
363 kW
38 Ω
80,7 Ω per phase
1,32 T
1,36 nF per phase
Calculation of inrush currents requires an adequate
modeling of the reactor nonlinear flux-current curve. The
nonlinearity is caused by the magnetizing characteristics of the
shunt reactor iron core. Recorded RMS voltage-current curve
The International Symposium on High-Voltage Technique "Höfler's Days", 7–8 November 2013, Portoroz, Slovenia.
550
500
450
400
350
300
250
Ln=256.77 mH
200
150
100
50 A'
0
0
250 500 750
Fig. 1.
reactor
L'air=96.997 mH
switching occurs at an instant near the voltage zero-crossing in
phase A, since it results with the maximum DC component of
current.
C'
B'
U (kV)
ψ (Vs)
obtained from manufacturer test data is converted into
instantaneous flux-current saturation curve (Fig. 1) which is
used in the nonlinear inductance model in EMTP-RV [6] and
approximated with two segments (linear area A’-B’, below
knee of the saturation curve and saturation area B’-C’).
2
1000 1250 1500 1750 2000 2250 2500 2750 3000
i (A)
Fig. 3. Shunt reactor voltages in case of reactor uncontrolled energization
Instantaneous flux-current saturation curve of 150 MVAr shunt
Model for analysis of shunt reactor switching in EMTP-RV is
shown in Figure 2.
A
m2
+VM
?v
R2
BUS1
+
a
RCu
b
+
SW1 ?i
+
6.66ms|15|0
10ms|15|0
13.33ms|15|0
?i
R1
110kVRMSLL /_0
+
RL1
RFe
+
+
AC1
Lnonl1
?if
L
c
m3
+VM
?v
+
R4
B
?i
Lnonl2
?if
L
+
L1
?i
+
3L0
+
+
RFe
Tr0_2
?i
R3
RCu
1
2
1
+
R6
C
m4
+VM
?v
Tr0_1
+
?i
R5
RCu
+
RFe
+
Lnonl3
?if
L
1
2
Fig. 4. Shunt reactor currents in case of reactor uncontrolled energization:
IAmax= 3455 A (3.10 p.u.), IBmax=-2982 A (2.68 p.u.), ICmax=-2494 A
(2.24 p.u.)
Conducted simulation shows that transient inrush current
with amplitude of 3.10 p.u. and high DC component can last
up to 3.5 seconds (Fig. 5). This could cause difficulties, such
as unwanted operation of the overcurrent relay protection.
+
A
m1
?i
1
ZVJ
Fig. 2. Model for analysis of shunt reactor switching in EMTP-RV
Each phase of a three phase shunt reactor is modeled as a
nonlinear inductance with serially connected resistance
RCu=146.5 mΩ, representing copper losses and parallel
connected RFe=133.3 kΩ, representing iron losses. Magnetic
coupling among the three star connected phases is represented
with zero sequence inductance L0=257 mH which provides a
path for the zero sequence current [7]. Equivalent 110 kV
network is represented with positive (R1=265 mΩ, L1=7 mH)
and zero (R0=216 mΩ, L0=5,7 mH) sequence impedances,
determined from single-phase and three-phase short circuit
currents: I sc1 = 33.8 kA∠ − 83.1o , I sc3 = 31.7 kA∠ − 83.1o .
B. Uncontrolled Energization
By uncontrolled energization the following instants of pole
closing were considered: tA=15 ms, tB=13 ms and tC=17 ms.
Figures 3 and 4 show shunt reactor voltages and currents,
respectively. The highest inrush current happened when
Fig. 5. Shunt reactor current in phase A in case of reactor uncontrolled
energization
Zero sequence current occurs in case of uncontrolled reactor
energization (Fig. 6) as a consequence of asymmetry. This may
cause the false operation of relay protection, used for detecting
single phase-to-ground faults.
3
Magnetic flux (Vs)
I (A)
The International Symposium on High-Voltage Technique "Höfler's Days", 7–8 November 2013, Portoroz, Slovenia.
Fig. 9. Magnetic flux in case of reactor controlled energization
Fig. 6. Zero-sequence current in case of reactor uncontrolled energization
Imax=-2052 A (1.84 p.u.)
C. Controlled Energization
Figures 7 and 8 show shunt reactor voltages and currents in
case of controlled energization at optimum instants of circuit
breaker poles closing at peak voltages (tA=10 ms, tB=6.66 ms
and tC=13.33 ms).
U (kV)
Fig. 10. The distribution of the magnetic flux in the five limb core of shunt
reactor - phase A (1), B (2) and C (3)
Conducted simulation shows that amplitudes and DC
components of inrush current (Fig 11) and zero-sequence
current (Fig 12) are significantly lower in case of controlled
switching. As a consequence, successfuly controlled switching
reduces the mechanical and electromagnetic stresses of the
high voltage equipment and also prevents the unwanted
operation of relay protection.
I (A)
I (A)
Fig. 7. Shunt reactor voltages in case of reactor controlled energization
t (s)
Fig. 11. Shunt reactor current in phase A
The current in phase A (Fig. 8) is slightly larger than in the
other two phases, due to the appearance of the DC component,
which is caused by initial magnetic flux in the core limb of that
phase at the moment of energization. This initial magnetic flux
is a part of a magnetic flux from the phase B, which is firstly
being switched on (Fig. 9). The final distribution of the
magnetic flux in the reactor core is shown in Fig. 10. Due to
the air gaps utilized in shunt reactor core there are no severe
saturation effects [8].
I (A)
Fig. 8. Shunt reactor currents in case of reactor controlled energization,
IAmax=-1260 A (1.13 p.u.), IBmax=1090 A (0.98 p.u.), ICmax=1123 A (1.01 p.u.)
Fig. 11. Zero-sequence current, Izmax=1122 A (1.01 p.u.)
4
The International Symposium on High-Voltage Technique "Höfler's Days", 7–8 November 2013, Portoroz, Slovenia.
III. TRANSIENTS CAUSED BY SWITCHING UNLOADED 400 KV
TRANSMISSION LINE
B. Model Description
Model for the analysis of switching the 231 km long 400 kV
unloaded transmission line [9] is shown in Fig. 14.
The equipment in high voltage substation was represented
by surge capacitances, whereas transmission lines, busbars and
connecting leads by a frequency depending line model [10].
The phase transpositions of the transmission lines have been
taken into account. The MO surge arresters were modeled with
nonlinear U-I curves for switching overvoltages.
The model of CB with two breaking chambers for switching
the transmission line 2 is shown in Fig. 15.
A. Measurements of switching transients
The measurements of switching transients caused by
uncontrolled switching of the 231 km long line were
performed. Figures 12 and 13 show recorded TRV and phase
voltages on line side in case of switching-off line by circuit
breaker equipped with grading capacitors.
800
Napon izmeðu kontakata prekidaèa (kV)
600
400
200
+
0.5
0.010nF
0
+
+
-200
+
0.5
0.010nF
+
+
1uH
1uH
-400
-600
-800
-0.05
0
0.05
SW8 ?vi
+
-1ms|10ms|0
0.1
SW9 ?vi
+
-1ms|10ms|0
0.01nF
400
+
+
+
Vrijeme (s)
Fig. 12. Recorded TRV in case of regular switching-off: UL1= -686 kV (2.08
p.u.),UL2=-657 kV (1.99 p.u.), UL3=641 kV (1.94 p.u.)
0.06nF
0.01nF
C13
C14
Fig .15.
Model of circuit breaker with C11
two braking chambers
300
The capacitance between the open contacts of breaking
chambers is 10 pF and inherent earth capacitances were taken
into account as depicted in Fig. 15.
100
0
-100
The equivalent networks were represented with a voltage
source in series with sequences impedances, which are
obtained from short circuit currents in case of switching state
prior to a fault (Table II).
-200
-300
-0.02
-0.01
0
0.01
Vrijeme (s)
0.02
0.03
0.04
0.05
Fig. 13. Recorded phase voltages on line-side after regular switching-off
UL1=360 kV (1.09 p.u.), UL2= 351 kV (1.06 p.u.), UL3= -348 kV (1.06 p.u.)
5.52nF
+
+
17.960nF
Capacitor voltage transformer 4400 pF
Current transformer 680 pF
Disconnector 200 pF
Post insulators in line bay 2x120 pF
Capacitor voltage transformer 4400 pF
Current transformer 680 pF
Disconnector 200 pF
Post insulators in line bay 2x120 pF
0.68nF
Transmission line 2
a
b
c
+
Equipment in transformer bay:
Autotransformer 2700 pF
Current transformer 680 pF
Circuit breaker 60 pF
Disconnector 200 pF
8 x post insulator 120 pF
Capacitor voltage transformer 4400 pF
+
a
b
c
FD
a
SW8 ?tT b
+
c
10ms|1|0
Connecting leads 510 m
672000
RL3
ZnO3
Main busbars 630 m
+
+
FD
+
418kVRMSLL /_0
ZnO +
672000
4.08nF
?vi
34x120 pF
Busbar post insulators
a
b
c
400 kV network equivalent
Transmission line 1
a
b
c
a
b
c
+
FD
RL5
a
b
c
a
b
c
+
RL6
+
400 kV network equivalent
RL4
a
+
+
c
FD
400 kV network equivalent
Transmission line 3
Transmission line 4
+
418kVRMSLL /_0
AC5
418kVRMSLL /_0
AC6
ZnO4
AC4
418kVRMSLL /_0
+
a
b
c
RL1
+
418kVRMSLL /_0
+
?vi
a a
b b
c c
+
FD
a
b
c
RL9
+
418kVRMSLL /_0
+
+
+
AC2
FD
a
b
c
12.640nF
Equivalent network 110 kV
AC3
+
AC9
Fig. 14. Model for analyzes of circuit breaker switching no-load 400 kV transmission line in EMTP-RV
684000
ZnO +
-0.03
+
-400
-0.04
ZnO +
Napon na NMT (kV)
200
?vi
ZnO1
5
The International Symposium on High-Voltage Technique "Höfler's Days", 7–8 November 2013, Portoroz, Slovenia.
TABLE II
SHORT CIRCUIT CURRENTS IN 400 KV SUBSTATION
Connections:
Transmission line 1 (86.3 km)
Transmission line 2 (231 km)
Transmission line 3 (91.5 km)
Transmission line 4 (152 km)
Power transformer
TR 1 (400/110 kV)
Power transformer
TR 2 (400/110 kV)
Total:
I3ph (kA/°)
3.4/-85.5
3.4/-85.5
2.4/84.8
4.1/-84.9
3.9/84.9
I1ph (kA/°)
2.4/-82.2
2.4/-82.2
1.8/-80.0
3.3/-79.9
3.0/-80.1
1.2/-81.5
1.3/-84.8
between breaking chambers is very important for CB dielectric
stresses during switching operations. Simulation results show
pretty unequal voltage distribution between breaking chambers
in phase L1 where the maximum peak of TRV occurs (Fig.
18).
m10a@vn
m10a@vn
m7a@vn
SW8@vb
87
7
6
6
5
5
1.1/-81.5
1.3/-84.8
4
4
19.5/-84.7
15.6/-81.6
33
22
C. Switching-off unloaded 400 kV transmission line
When an unloaded line is regularly switched-off the electric
arc distinguishing occurs at current natural zero-crossing. Fig.
16 shows phase voltages on line-side after regular switchingoff. Voltage is highest in the phase which is firstly switchedoff due to the electromagnetic coupling of the other phases and
due to Ferranti effect.
4004
L3
m7c@vn
11
0
0
−1
−1 0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Fig. 18. Distribution of CB recovery voltage between breaking chambers
The voltage distribution between the breaking chambers
could be improved by installing the grading capacitors, which
are especially important in cases when switching-off relatively
long lines. Further analyses show the influence of grading
capacitors of 500 pF on voltage distribution. Simulation results
show significant improvement of voltage distribution and
reduction of TRV amplitude (Fig. 19).
m7b@vn m7a@vn
L2
L1
30034
3
2002
2
1001
1
000
-100−1−1
-200−2−2
m10a@vn
m10a@vn
4.5
4
4
-400−4−4
3.5
3.5
−5
-500−5 00
0
m7a@vn
4.5
8
-300−3−3
0.01
0.01
10
0.02
0.02
20
0.03
0.03
30
0.04
0.04
40
0.05
0.05
Time (s)
0.06
0.06
0.07
0.07
0.08
0.08
50
60
70
80
t (ms)
Fig. 16. Phase voltages on line-side after regular switching-off
0.09
0.09
90
0.1
0.1
3
3
100
2.5
2.5
22
1.5
1.5
Since the capacitor voltage transformers are installed on
both sides of the line the discharging of trapped charge is slow.
Such discharging depends on weather conditions, mainly on
humidity. So, the trapped charge has a very significant
influence on CB transient recovery voltage (Fig. 17).
m10c@vn−m7c@vn
m10b@vn−m7b@vn
11
0.5
0.5
0
0
−0.5
−0.5 0
0
0.01
0.01
0.02
0.02
0.03
0.03
0.04
0.04
0.05
0.05
0.06
0.06
0.07
0.07
0.08
0.08
0.09
0.09
0.1
0.1
Fig. 19. Distribution of CB recovery voltage between breaking chambers in
case with grading capacitors
m10a@vn
8
Fig. 20 shows the comparison of calculated TRV peak
values in cases with and without grading capacitors.
8
6
6
4
4
2
2,5
2
Total TRV
2
−2
−2
Without grading capacitors
(Chamber 1)
U (p.u.)
1,75
−4
−4
−6
−6
−8
−8 0
0
Maximum withstand voltage 2,4 p.u. (823 kV)
2,25
0
0
0.01
0.01
0.02
0.02
0.03
0.03
0.04
0.04
0.05
0.05
0.06
0.06
0.07
0.07
0.08
0.08
0.09
0.09
0.1
0.1
1,5
Without grading capacitors
(Chamber 2)
1,25
1
With grading capacitors
(Chamber 1)
0,75
With grading capacitors
(Chamber 2)
0,5
Fig. 17. TRV in case of regular switching-off: UL1=758 kV (2.32 p.u.),
UL2=713 kV (2.18 p.u.), UL3=692 kV (2.12 p.u.)
0,25
0
1
2
3
Phase
Besides the peak value of TRV the voltage distribution
Fig. 20. Calculated TRV when switching-off unloaded 400 kV line
The International Symposium on High-Voltage Technique "Höfler's Days", 7–8 November 2013, Portoroz, Slovenia.
The CB should withstand the maximum voltage of 823 kV
(2.4 p.u.) across the open contacts [11]. Compared to this, the
computed value of recovery voltage is only 10 % smaller
(758 kV/2.2 p.u.). However, the greatest part (nearly 80 %) of
TRV stresses the breaking chamber closer to the substation.
D. Energization of unloaded 400 kV transmission line without
trapped charge
Energization and auto-reclosure of long transmission lines
can cause undesirable overvoltages in the transmission
network, so special overvoltage mitigation measures are
employed to meet the insulation coordination considerations.
The most common practice has been to use metal-oxide surge
arresters and circuit breakers equipped with closing resistors,
but this solution is relatively expensive.
Worst case of uncontrolled energization at peak voltage in
all phases is analyzed. Figure 21 shows voltages at the end of
transmission line without surge arresters in case of
uncontrolled switching.
6
TABLE III
SWITCHING OVERVOLTAGE AMPLITUDES AT THE END OF UNLOADED LINE
IN CASE OF ENERGIZATION WITHOUT TRAPPED CHARGE
Voltage amplitude (kV)
Uncontrolled switching
Controlled switching
UL1
UL2
UL3
UL1
UL2
UL3
Without surge
752
803
723
arresters
392
401
397
With surge
634
630
632
arresters
Controlled energization at optimum instants of circuit breaker
poles closing at voltage zero-crossing is simulated. Figure 23
shows voltages at the end of the line for this case.
Fig. 23. Voltages at the end of transmission line in case of controlled
switching
Fig. 21. Voltages at the end of transmission line without surge arresters in
case of uncontrolled switching
E. Auto-reclosure of unloaded 400 kV transmission line
In the case of transmission line with a capacitive potential
transformers connected at both ends, no leakage path exists for
the trapped charge. Figure 24 shows voltages at the end of
transmission line without surge arresters in case of
uncontrolled switching.
Figure 22 depicts voltages at the end of transmission line
with surge arresters Ur=342 kV in case of uncontrolled
switching.
Fig. 24. Voltages at the end of transmission line without surge arresters in
case of uncontrolled switching
Fig. 22. Voltages at the end of transmission line with surge arresters in case
of uncontrolled switching
Table III shows the comparison between uncontrolled and
controlled switching regarding the amplitudes of switching
overvoltages at the end of the unloaded line. It can be seen that
switching overvoltages are significantly lower in case of
controlled switching.
Contact closing occurs at voltage peak on the source-side of
the opposite polarity to the trapped charge. This represents the
most severe case of uncontrolled auto-reclosure.
Figure 25 shows voltages at the end of transmission line
with surge arresters in case of uncontrolled switching. The
optimum instant of circuit breaker switching is the voltage
peak on the source-side of the same polarity as the trapped
charge (Fig. 26).
The International Symposium on High-Voltage Technique "Höfler's Days", 7–8 November 2013, Portoroz, Slovenia.
7
protection.
REFERENCES
[1]
Fig. 25. Voltages at the end of transmission line with surge arresters in case
of uncontrolled switching
Fig. 26. Voltages at the end of transmission line in case of controlled
switching
Table IV shows the comparison between uncontrolled and
controlled switching regarding the amplitudes of switching
overvoltages at the end of the unloaded line. It can be seen that
switching overvoltages are significantly lower in case of
controlled switching.
TABLE IV
SWITCHING OVERVOLTAGE AMPLITUDES AT THE END OF UNLOADED LINE
IN CASE OF AUTO-RECLOSURE
Voltage amplitude (kV)
Uncontrolled switching
Controlled switching
UL1
UL2
UL3
UL1
UL2
UL3
Without surge
1027
1115
1363
arresters
386
375
368
With surge
663
671
609
arresters
IV. CONCLUSION
This paper describes switching transients caused by
uncontrolled and controlled switching of high-voltage circuit
breaker. Switching of shunt reactor and no-load transmission
line was analyzed using EMTP-RV software.
Amplitudes and DC components of inrush currents and
zero-sequence current are significantly lower in case of reactor
controlled switching compared to uncontrolled switching.
Switching-off, energization and auto-reclosure of unloaded
400 kV transmission line was presented. Controlled switching
generates significantly lower overvoltages.
As a consequence, controlled switching reduces the
mechanical and electromagnetic stresses of the high voltage
equipment and also prevents the unwanted operation of relay
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Due to Switching of 400 kV Shunt Reactor”, International Conference
on Power System Transients (IPST), Rio de Janeiro, Brazil, June 24-28,
2001.
[2] Karcius M. C. Dantas, Washington L. A. Neves, Damásio Fernandes Jr.,
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39–61, 1995.
[4] Mitsubishi Electric Advance: “Controlled Switching System”, Vol.117,
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Washington, 2003
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[8] ABB, “Controlled Switching, Buyer´s & Application Guide”, Edition 4,
2013.
[9] S. Bojić, I. Uglešić, B. Filipović-Grčić, “Switching Transients in
400 kV Transmission Network due to Circuit Breaker Failure”,
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Vancouver, Canada, July 18-20, 2013.
[10] Ali F. Imece, D. W. Durbak, H. Elahi, S. Kolluri, A. Lux, D. Mader, T. E.
McDemott, A. Morched, A. M. Mousa, R. Natarajan, L. Rugeles, and E.
Tarasiewicz, "Modeling guidelines for fast front transients", Report
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[11] IEC 62271-100: High-voltage switchgear and controlgear; High-voltage
alternating-current circuit-breakers, 2003.