© 2017 Siemens Industry, Inc. All rights reserved.

Tab 2 – Voltage Stresses – Switching Transients

Distribution System Engineering Course – Unit 10

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-2

Transient Overvoltages

n Decay with time, usually within one or two cycles

n Often called surges

n The two most common types of transient overvoltages:

- Switching Surges

- Lightning Surges

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-3

Time Functions & Transients

n Transient analysis considers many typesof time varying functions:

- Sine & Cosine waves

• Power frequency

• Harmonic frequency

• Resonant frequncy

- Unit Step function

- Exponential functions

- Surge functionsSiemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-4

Switching Surges

n Generally contain frequencies from power frequency to tens of kHz

n Caused by the closing or opening of switching equipment (circuit breakers,

disconnectors, etc.):

- Energizing of

• lines

• cables

• transformers

• reactors

• buses

- Line re-energization or high speed reclosing

- Circuit breaker transient recovery voltages (TRV)

- Faults Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-5

The Ideal Circuit Breaker or Switch Model

When closed When open

Z = 0

Y = 0Y = 0

Z = ¥

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-6

Closing

n 120 V equipment will not conduct until metal-to-metal contact is made

n HV equipment will pre-strike when the dielectric strength of the gap between the

contacts is less than the instantaneous applied voltage

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-7

Energize Capacitor Bank at Various Angles:

Voltages

(file capclose0.pl4; x-var t) v:CAP 90- v:CAP 45- v:CAP 00- v:SINE0 4 8 12 16 20[ms]

-150

-100

-50

0

50

100

150

200

[V]

+VSiem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-8

Energize Capacitor Bank at Various Angles:

Inrush Currents

(file capclose0.pl4; x-var t) c:CAP 90- c:CAP 45- c:CAP 00-0 4 8 12 16 20[ms]

-0.700

-0.525

-0.350

-0.175

0.000

0.175

0.350

0.525

0.700

[A]

+VSiem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Three-phase voltages and currents

captured by event recorder

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Switching Surges

(f ile E1FIG1.pl4; x-v ar t) v :LINOGB0 10 20 30 40 50 60 70 80[ms]

-200

-150

-100

-50

0

50

100

150

200[kV]

- Have only one (or just a few) significant peaks

- Have damped high frequency (100 Hz to 10 kHz) components superimposed on the power

frequency voltage

- Waveform from an EMTP simulation of a line energization

Steady state 60 Hz

- Peak of the surge

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Switching Surge Results Are Statistical

- A switching surge magnitude and waveshape depends upon the instant in time that the circuitbreaker closes.

- Computer simulations can be repeated with various closing times to obtain a statistical distributionof the overvoltages.

0.5%1.0%

2.0%

5.0%

10.0%

20.0%

30.0%

50.0%

60.0%

70.0%

80.0%

90.0%

95.0%

98.0%

99.0%99.5%

40.0%

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2

V (pu)

prob

abili

ty o

f exc

eedi

ng V

0 11111

2-11Siem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-12

Closing Resistors or Reactors

n Some equipment uses closing resistors or reactors to reduce transients

n Applications

- capacitor banks

- EHV lines

Pre-insertion impedance

Closes 1st Closes 2nd

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Analysis of a Voltage Waveform

• Three phase to ground and neutral voltages at the substation bus from simulation of an SLG fault on a network

feeder.

(f ile OA1.pl4; x-var t) v:NQBUSA v:NQBUSB v:NQBUSC v:NQBUSN0.00 0.04 0.08 0.12 0.16 0.20[s]

-35.00

-26.25

-17.50

-8.75

0.00

8.75

17.50

26.25

35.00[kV]

21.21 kV = 1 pu

Steady state voltages

Fault starts at peak of A phase

Peak of C phase switching surge from fault is 32.8

kV (1.547 pu)

TOV during fault is highest on B

PhaseAlmost back to steady state

voltages

Switching surges from fault

clearing

2-13Siem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Saturation Curve for Transformer

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0 10 20 30 40 50 60 70 80 90 100

Peak Current on LV Winding [kA]

Flux

[Web

ers]

0.47 Wb, 1 kA

air coreinductance

ΦΦ voltageΦ-N voltage

2-14Siem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Simulation of a large autotransformer

energizing in a weak system

PSCAD Graphs

0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 ... ... ...

-2.00-1.50-1.00-0.500.000.501.001.502.00

V (

pu)

V at CB

-0.40

0.60

i (kA

)

CB a CB b CB c

-0.100-0.0500.0000.0500.1000.1500.2000.250

i (kA

)

I SA

Surge arrester energy >1.4 MJ

2-15Siem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Simulation of a large autotransformer

energizing in a weak system

PSCAD Graphs

0.190 0.200 0.210 0.220 0.230 0.240 0.250 0.260 0.270 ... ... ...

-2.00-1.80-1.60-1.40-1.20-1.00-0.80-0.60-0.40-0.200.000.200.400.600.801.001.201.401.601.802.00

V (p

u)

V at CB

2-16Siem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Three-phase set of waveforms of inrush currents from transformer energizing

simulation

(file shot0040.pl4; x-var t) c:NQBUSA-1Q070A c:NQBUSB-1Q070B c:NQBUSC-1Q070C0.00 0.04 0.08 0.12 0.16 0.20[s]

-5000

-3750

-2500

-1250

0

1250

2500

3750

5000

[A]

2-17Siem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-18

The Physics of the Interrupting Process

n Process starts when the metallic contacts part

n The last contact point melts & evaporates

n An arc is formed between the contacts

n Arcs contain a high temperature ionized gas (plasma)

n Arcing continues until it is extinguished

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-19

Arc Extinguishing

n Arc cooling exceeds arc heating

n Generally occurs at a current zero

-150

-100

-50

0

50

100

150

time

A

current zero

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-20

Current Chopping

0

2

4

6

8

10

12

time

A

current chop -

- no chop

normal current zeroSiemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-21

Recovery Voltage

n Current interruption is immediately followed by a voltage across the contacts

n In a very short time, the conducting gas must change into an insulating medium

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-22

Resistive Load Switching

n Relatively easy duty

-150

-100

-50

0

50

100

150

time

current

system voltage/

interruption at current zero/

/recovery voltageSiem

ens

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-23

-1.5

-1

-0.5

0

0.5

1

1.5

time

current/

2.0 purecoveryvoltage

capacitor voltage \

-system voltage

Capacitive Current Switching

• Current zero interruption leaves a 1 pu trapped charge on the capacitor

• Recovery voltage reaches 2 pu on 1 phase circuitsSiemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-24

-1.5

-1

-0.5

0

0.5

1

1.5

time

current/

2.0 purecoveryvoltage

reactor voltage -

system voltage \

Inductive Current Switching

n Relatively small currents

n High frequency transient recovery voltage

n current chopping can create very high overvoltages

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-25

Fault Current Interruption

n CBs must safely handle very high magnitude currents

n CBs must open quickly to minimize the impact of the fault on the system

Fault

Siemen

s

Uni

t10-

Ligh

tnin

g an

d S

urge

Pro

tect

ion

©20

17 S

iem

ens

Indu

stry

, Inc

., S

iem

ens

PTI

Mar

ch 2

017

Siemens Industry, Inc., Siemens Power Technologies International 2-26

Transient Recovery Voltages (TRV)

-1

-0.5

0

0.5

1

1.5

2

2.5

time

\current

switch recovery voltage -

system voltage \

0

10

20

30

40

time

average rate of rise

crest

initial rate of rise

Siemen

s