Using Simulation Tools to Predict and Prevent Vacuum Circuit Breaker Switching Induced Transformer...

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

DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited

2

Concerns with Switching Transformers at Medium-Voltage

5/21/2015ISS 2015: VCB Switching;

Distribution A: Approved for public release; distribution is unlimited

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

3

Overview



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

4

Above 1000 Volts, new concerns arise with switchgear applications and transients.



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.

5

VCBs can “chop” several Amperes of current; producing overvoltages that are mitigated with capacitance.



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

6

Dry-type transformers reduce weight and risk of fire, but are not as well insulated as oil-filled transformers.



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

7

The circuit model has to include transient (or high-frequency) behavior of VCB, cable and transformer.



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

8

The Alternative Transients Program (ATP) supports detailed studies, with no software licensing cost.



www.emtp.org

MATLAB / SimPowerSystems also works, but use the “Specialized Technology Library”

9

Text-based modeling language code in ATP reproduces the multiple re-ignition behavior of the VCB.



(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.

10

Transformer voltage reduced from 61 kV (red) to 17 kV (green) by adding an RC snubber (0.125 mF, 50 W)



chop1.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.

11

Chop4.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.



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.

12

A caveat with RC snubbers; more capacitance can worsen ferroresonance if one or two poles of the VCB delay opening.



(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.

13

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



Using Simulation Tools to Predict and Prevent Vacuum Circuit Breaker Switching Induced Transformer...

Documents

Transcript of Using Simulation Tools to Predict and Prevent Vacuum Circuit Breaker Switching Induced Transformer...