Using Simulation Tools to Predict and Prevent Vacuum Circuit Breaker Switching Induced Transformer Failures
Steven B. Swindler, [email protected] J. Dionise, [email protected] A. Johnston, [email protected] E. McDermott, [email protected]
Intelligent Ships Symposium; May 21, 2015
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Concerns with Switching Transformers at Medium-Voltage
5/21/2015ISS 2015: VCB Switching;
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Due to a high prevalence of medium-voltage (MV) transformer internal winding failures in industry, IEEE developed IEEE Std C57.142™-2010: IEEE Guide to Describe the Occurrence and Mitigation of Switching Transients. C57.142 identifies the following conditions as indicating a vulnerability to switching-induced transformer failures
1. Switching device directly connected via cable to 1 or 2 transformers2. Transformer unloaded, lightly loaded, or feeding non-linear loads3. Load, when switched, is primarily inductive 4. Switching produces oscillations near transformer natural frequencies5. Long or short cables between switch and transformer (many papers indicate
that short cables are worse from an oscillation perspective)6. Load is switched frequently
Additionally, vacuum circuit breakers (VCBs) typically used on MV systems have characteristics that may exacerbate switching oscillations
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Overview
5/21/2015ISS 2015: VCB Switching;
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1. Unique concerns of medium-voltage electric power systems2. Vulnerability of dry-type transformers3. Transient-producing behavior of vacuum circuit breakers4. Mitigation with surge arresters and RC snubbers5. New tests and simulations in the design process
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Above 1000 Volts, new concerns arise with switchgear applications and transients.
5/21/2015ISS 2015: VCB Switching;
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M
M
LC42
LC12
LC21
LC31
LC32
LC22
LC41
LC11
IPS2
IPS4
IPS1
IPS3
TIEATIEB
IM136.5 MW4.16 kV
IM236.5 MW4.16 kV
ATG44 MW13.8 kV
ATG34 MW13.8 kV
MTG236 MW13.8 kV
MTG136 MW13.8 kV
0
5
10
15
20
25
30
0 10 20 30 40 50 60 70 80
TRV for 14-kA Fault at IPS2 Bus
Volta
ge (k
V)
Time (us)
T100 Rating TRV (1 nF) TRV (40 nF) T70 Rating
2011 ISS IX Example:Mitigating TransientRecovery Voltage (TRV)With Bus Capacitance.
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VCBs can “chop” several Amperes of current; producing overvoltages that are mitigated with capacitance.
5/21/2015ISS 2015: VCB Switching;
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VCB
Cxf Lm Rm
Ichop
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
5 50 500
Peak
Vol
tage
[kV]
Cable Length [ft]
1 pF
0.5 nF
1 nF
2 nF
5 nF
10 nF
0.125 uF
0.25 uF
Adding Capacitance Suppresses the Peak Transient Voltage
Predictions of necessary capacitance from hand calculations of simplified circuit.
2 21 1
2 2m chop xf peakL I C V
m
xf
LZ C
*peak chopV Z I
12 m xf
fL C
mRZ
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Dry-type transformers reduce weight and risk of fire, but are not as well insulated as oil-filled transformers.
5/21/2015ISS 2015: VCB Switching;
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0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03
Cres
t Vol
tage
[kV]
Time to Crest [s]
Transformer/Arrester Coordination
Liquid Xfmr
Dry Xfmr
Dist Arr
Station Arr
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The circuit model has to include transient (or high-frequency) behavior of VCB, cable and transformer.
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Zsrce Cable
VCB
GeneratorsRsnub
Csnub
Cxf Lm RmCTRV
v’Z’=V/I
R’d
d
L’d
C’d/2 C’d/2
Distributed-Parameter Cable Transformer Frequency Response Analysis
Arrester
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The Alternative Transients Program (ATP) supports detailed studies, with no software licensing cost.
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www.emtp.org
MATLAB / SimPowerSystems also works, but use the “Specialized Technology Library”
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Text-based modeling language code in ATP reproduces the multiple re-ignition behavior of the VCB.
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(f ile Reignite.pl4; x-v ar t) v :XFHIC - 0.0 0.2 0.4 0.6 0.8 1.0[ms]
-50.0
-37.5
-25.0
-12.5
0.0
12.5
25.0
37.5
50.0
[kV]
Oscillatory voltages;No RC snubber.
(f ile Reignite.pl4; x-v ar t) c:MEAS -VCBC 0.29 0.30 0.31 0.32 0.33 0.34 0.35 0.36 0.37[ms]
-800
-600
-400
-200
0
200
400
600
800
[A]
High-frequencycurrent interruptions;No RC snubber.
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Transformer voltage reduced from 61 kV (red) to 17 kV (green) by adding an RC snubber (0.125 mF, 50 W)
5/21/2015ISS 2015: VCB Switching;
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chop1.pl4: v :XFHIC -
chop2.pl4: v :XFHIC -
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0[ms]-75
-50
-25
0
25
50
[kV]
Chopping transformer magnetizing current; 1.13 Amps.
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Chop4.pl4: v :XFHIC -
chop3.pl4: v :XFHIC -
chop5.pl4: v :XFHIC -
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0[ms]-150
-100
-50
0
50
100
150
[kV]
The VCB may chop up to 5 Amperes, which increases the transient voltage.
5/21/2015ISS 2015: VCB Switching;
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Chopping 5 Amps; opening under light load.
150 kV with no mitigation.
20 kV with Arrester only, but high-frequency oscillations. 51 kV with RC snubber only, and
slower oscillations.
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A caveat with RC snubbers; more capacitance can worsen ferroresonance if one or two poles of the VCB delay opening.
5/21/2015ISS 2015: VCB Switching;
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(f ile Ferro1.pl4; x-v ar t) v :XFHIA - v :XFHIB - v :XFHIC - 0.00 0.02 0.04 0.06 0.08 0.10[s]
-50.0
-37.5
-25.0
-12.5
0.0
12.5
25.0
37.5
50.0
[kV]
Sustained non-linear overvoltages may cause transformer or other equipment to fail.
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Conclusion – new engineering concerns arise with adoption of medium-voltage electric power systems.
• This is still new to the Navy– Consult IEEE Standards C37.011, C57.142, C62.22
• Needs for transient simulation– Non-linear effects of transformers, switchgear, loads and
possibly surge arresters– Optimize the R and C parameters of a snubber– Investigate high-resistance grounding
• Needs for new tests– Transformer / system interactions– Require frequency response tests (SFRA) on new
transformers
5/21/2015ISS 2015: VCB Switching;
Distribution A: Approved for public release; distribution is unlimited