Vacuum circuit breaker switching

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Aug 30, 2018 - transformers (step-up and power transformer) ... Evaluate voltage protection margins ..... Example 3 – lightning current distribution / ionization ...
Insulation coordination for wind power plants EMTP-RV Satelite meeting Paris, FRANCE – August 30, 2018 Prof. Dr. Ivo Uglešić Božidar Filipović-Grčić, PhD Bruno Jurišić, PhD Nina Stipetić, mag.ing. Faculty of Electrical Engineering and Computing University of Zagreb, Croatia

Overview

• Insulation coordination definition • Wind Power Plant characteristics • Challenges of insulation coordination in WPPs

• Examples in EMTP-RV ✓Temporary overvoltage due to SLGF ✓Vacuum circuit breaker switching ✓Direct lightning strikes

1

Insulation coordination • The goal of insulation coordination is uninterrupted and reliable power supply in all technical and atmospheric conditions.

• Definition by IEC 60071-1: ✓ Insulation coordination is the selection of the dielectric strength of equipment in relation to the voltage which can appear on the system for which the equipment is intended and taking into account the service environment and characteristics of the available protective devices. ✓ The insulation in a power system (with all its components) should be designed on the way to minimize damage and interruption to service as a consequence of steady state and transient overvoltages and this should be done economically. 2

Wind power plant characteristics • • • •

Transmission system: MVAC, HVAC, HVDC Collector system: MVAC cable network, different topologies Reactive compensation, filters at POI Main components: ✓ wind turbine generators (Type 1 – Type 5) ✓ vacuum circuit breakers ✓ transformers (step-up and power transformer) ✓ cables

3

WPP – typical layout LV/MV step-up transformers

substation MV/HV transformer

feeder breakers

WTGs 4

Overvoltages in WPPs Lightning transients

✓ Coupling through substation transformer ✓ From direct tower strikes

Switching transients

✓ Coupling through substation transformer ✓ Feeder energization ✓ Vacuum circuit breaker switching (VFFT due to prestrikes and restrikes)

Surge arrester selected to protect equipment from these

Temporary overvoltages

✓ Ground faults ✓ Feeder islanding, loss of ground reference ✓ Can be higher than 1.73 pu

Continuous operating voltages ✓ Higher voltage at remote ends

Surge arrester selected to survive these

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Surge arrester typical placement in MV network • adjacent to the substation power transformer • on the feeder side of each feeder breaker • at each interface between overhead and underground feeder sections • at the end of each feeder and branch + LV surge arresters in the tower

6

Insulation coordination steps Conventional process from standards (IEEE C62.22, IEC 60071)

Procedure for WPPs

1. Select the surge arrester to be used 1. Select the available insulation level (MCOV, TOV) (limited range)

2. Determine the protective level of selected surge arrester

2. Select arresters needed to protect that insulation level

3. Determine the locations for surge arresters

3. Determine amount of TOV that can be withstood

4. Determine the voltage at terminals of the protected equipment 5. Select equipment insulation level

TOV mitigation methods

Evaluate voltage protection margins

if margins are inadequate, consider alternatives: different arrester locations, higher insulation level... 7

Temporary overvoltage due to SLGF

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Example 1

Temporary overvoltage: single-line-toground fault, feeder disconnection and loss of ground reference

1.

2. 3. 9

Example 1 • Overvoltage of healthy phases depends on grounding and WTG type • TOV mitigating options: ✓ Transfer tripping (normaly used in new WPPs) ✓ High-speed grounding switch ✓ Grounding transfomer on each feeder

• The choice depends on WTG type

R. Walling, WESC 10

Example 1 WTG voltage measurement

ynD 0.69/33 kV

VCB X

33 kV cable network

GT2

fault

dYn 33/132 kV

GT1

0.69kV /_0

+ VwZ1

0.69kV /_0

+ VwZ11

FDQ

FDQ

+

FDQ

+

SW27

-1|1E15|0

+

SW28

-1|1E15|0

CABLE DATA

FDQ

2

+3 0

33/0.69

1 +

SW26

?v m2 +VM DEV9

Vacuum circuit breaker model

FDQ

m3 + ?i A

+A

m1

a b c

?i

FDQ14 +

a

c b a

BUS_A1

FDQ15 +

m10 +VM

-1|200ms|0

+3 0

1 +

33/0.69

2 FDQ

-1|210ms|0

SW29 a b c

FDQ16 +

cabledata6

CABLE DATA model in: cable_sc_100m_33_6fd_rv.pun

?v/?v/?v

BUS_A2

c b a

+

SW4

-1|1E15|0 +3 0

33/0.69

2

FDQ17

+

+

SW31

SW30 a b c

BUS_A3

c b a

a b c

FDQ18 +

-1ms|220ms|0

-1ms|225ms|0

SW32 a b c

+

1 +

c b a

+

SW33

-1|230ms|0

FDQ19

BUS_A4

cabledata4

CABLE DATA model in: cable_33_800_6ph_fd_rv.pun

?v

c -1ms|215ms|0 b a

+

-1|1E15|0

SW11

2

+3 0

33/0.69

+

SW12

-1|1E15|0 +3 0

1

1

2

33/0.69

1

+3 0

2 FDQ

BUS_A5

c b a

a b c

BUS_A6

FDQ20 +

33/0.69

+

SW19

-1|1E15|0

+

-1|1E15|0

SW20

2

+3 0

33/0.69

1 +

SW34 BUS_A7

a b c

?v

c -1ms|215ms|0 b a

m11 +VM

m8 +VM

FDQ13 a a +

FDQ

b b

Slack: 132kVRMSLL/_0

DEV10

LF

Vacuum circuit breaker model

FDQ12

b 1

2

+

+3 0

DEV11

1nF

FDQ

FDQ2 +

FDQ

?vi>e

?i 2,4Ohm

RL9

?i

+

scope scp1 ?s scope scp2 ?s scope scp3 ?s

+

e_ZNOa

?i

ZNOa

1

+

R17

arrester abb.dat

R18 + 100M

1

+ 100M

R16 + 100M

1

+

1

Tr0_9

+

1

Tr0_8

2

2

+ 1

2

1m

R15 +

1m

R14 +

R13 + 1m

+

20ms|120ms|0 SW36 ?vi

+

20ms|1E15|0 SW37 ?vi

1m

R21 +

1m

R20 +

A

?i m13 +

m12 +A ?i

R19 + 1m

Tr0_7

1

1

2

2

Tr0_12

+

C2

Data function

1

+

1

Tr0_11

2

1

+

1nF

66000

2,4Ohm

ZnO

1

+

e_ZNOc

model in: arrester abb.pun

Tr0_10

33/132

RL7

ZNOb

2,4Ohm

?vi>e 66000

R22 + 100M

+

+

e_ZNOb

R24 + 100M

RL8

+ RL10

?i 12,25Ohm

+ RL11

?i 12,25Ohm

+ RL12

ZNOc

Zn O

?i 12,25Ohm

?vi>e 66000

Zn O

Zn O

+

R23

C1

c

+

SW38 ?vi

20ms|1E15|0

Vacuum circuit breaker model

+ 100M

a b c

DY_2

c c

+

0.69kV /_0

+ VwZ12

0.69kV /_0

+ VwZ13

0.69kV /_0

+ VwZ14

0.69kV /_0

+ VwZ15

0.69kV /_0

+ VwZ16

+ VwZ17 +

-1|1E15|0 +3 0

2

cabledata5

33/0.69

1 +

SW35 c

a b

BUS_A8

c -1ms|500ms|0 b a

SW21

0.69kV /_0

Grounding transformer zig-zag

11

a b c

LF1 Phase:0 132kVRMSLL /_0 BUS: VwZ10

+

Example 1 – GT 2 excluded 1. SLGF occurs at 20 ms on phase C 2. Feeder breaker opens at 100 ms – loss of ground reference 3. WTGs continue to generate

overvoltage limited

1.

2.

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Example 1 – GT included 1. SLGF occurs at 20 ms on phase C 2. Feeder breaker opens at 100 ms – loss of ground reference 3. WTGs continue to generate

overvoltage remains limited

1.

2.

13

Vacuum circuit breaker switching

14

Practical problems with VCB switching in wind farms • The first off-shore wind farms were faced with substantial transformer failures in a very early operation stage. • In the first large offshore wind farms Horns Rev and Middelgrunden (Denmark), almost all of the transformers had to be replaced due to insulation failures. • It is suspected that the switching of the vacuum circuit breakers (VCB) caused the transformer failures. • In order to investigate this phenomenon, a laboratory setup was built, designed to give an insight into high frequency transients generated during breaker switching in offshore wind farms and similar cable systems. „ELECTRICAL TRANSIENT INTERACTION BETWEEN TRANSFORMERS AND THE POWER SYSTEM”, CIGRE WG A2/C4.39 15

Vacuum circuit breaker switching

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Restrike phenomena during breaking of small inductive current

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Restrikes caused by VCB switching

„ELECTRICAL TRANSIENT INTERACTION BETWEEN TRANSFORMERS AND THE POWER SYSTEM”, CIGRE WG A2/C4.39

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Example 2 – Failure of power transformer 110/25 kV

Failure of 25 kV winding

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Example 2 – EMTP-RV model • Detailed model of VCB • Detailed model of power transformer (high-frequency behaviour)

Power transformer VCB MV cable network (capacitive load) GND ZnO1 ZnO

72600

+ model in: polimh29.pun

ZnO

72600

+

SS2

4

State Space

d__2

VCB DEV1

Trafo -A5

+VM m1 ?v

Vacuum circuit breaker model

C2

110 kV network

Data function

Power transformer

+

+ 3.5uF

110kVRMSLL /_0

d__1 d__2 c d__4

+

+

a b c

ZnO

AC2

GND ZnO2

0.100nF GND

C3

L1 GND

482mH

Cable network 20

Simulation results

VCB voltage 21

Simulation results

VCB current 22

Simulation results

VCB current 23

Simulation results

Overvoltage at 25 kV winding of power transformer 24

Simulation results

Overvoltage at 25 kV winding of power transformer

25

Direct lightning strike to wind turbine

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Damages caused by direct lightning strike

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Lightning and surge protection for the wind turbine

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Placement of the SPDs

Example: protection for the generator

SPD according to EN 61643-11/IEC 61643-11

type 2/class II

Nominal AC voltage (Un)

480 V (50/60 Hz)

Max. continuous operating voltage (Uc)

600 V (50/60 Hz)

Nominal discharge current (8/20 µs) (In)

15 kA

Max. discharge current (8/20 µs) (Imax)

25 kA

Voltage protection level (UP)

≤ 3 kV

Temporary overvoltage (TOV)

900 V / 5 sec. 29

Example 3 – Direct lightning strike to WT blade Single WTG 3 MVA operating in the vicinity of substation 22/110 kV. Lightning current 100 kA ?i Icigre1

w1B1a +VM ?v w1B1b +VM ?v w1B1c +VM ?v

+

BUS2

C4

CP

40

TLM4

BUS7

m2 +VM ?v

SM

a b c

+

FDQ

a b c

1

a b c

2

TR2 22/110 kV 15 MVA BUS4

m4 +VM ?v

YD_1

LV_cable

22 kV cable 2 km

BUS3

+

SM1

+

Blade 40 m

WTG 3 MVA

m1 +VM ?v

TR1 0.69/22 kV 3 MVA 2.464nF

100kA/3us

FDQ2 +

BUS3 m5 +VM ?v

DY_1

FDQ

1 a b c

2 +30

22/110

123kVRMSLL /_0

-30

CP

80

TLM3

CABLE DATA model in: lv_cable_rv.pun

f(u)

2.21nF

+

C3

1.155nF

GND

C2

GND

CABLE DATA model in: cabledata1_rv.pun

i

1

?vi + VwZ1

cabledata1

0,7 kV cable 80 m

+

Tower 80 m

+

0.69/22

110 kV network

Fm1

f(u)

C1

0.02

1 2

?vi

+ 700

ZnO

c

1

Fm2 select

Sel1

ZnO1

+ Y Y I

Rn1 I ?vi>i

0.04 GND

model in: arresterlv.pun

ZnO Data function

GND

SPD

Grounding resistance 50 Ω (ionization included)

30

Example 3 – lightning current distribution / ionization

Lightning current

Potential rise at grounding resistance

Current through grounding resistance

Grounding resistance

31

Example 3 – overvoltages at TR1 and WTG terminals

Overvoltages at 0.69 kV side of TR1

Transferred overvoltages at 22 kV side of TR1

Overvoltages at WTG terminals 32

Example 3 – SPD connected in neutral point of TR1 and ideally grounded

Overvoltages at 0.69 kV side of TR1

Transferred overvoltages at 22 kV side of TR1

Overvoltages at WTG terminals 33

Conclusion • Different approaches for reducing TOVs due to SLGF are investigated. Simulations have shown that application of grounding transformer efficintly reduces TOVs during SLGF. • EMTP-RV simulations confimed the fact that VCB switching produces VFTOs which are not high in magnitude, but due to high freqency, the distribution across the transformer winding is nonlinear. This may cause dielectric breakdown of transformer insulation system. • The results of direct lightning strike simulation indicate that use of appropriate SPDs is crucial in order to protect the vulnerable electronic equipment. However, the efficient operation of SPDs depends on grounding resistance value which should be kept as low as possible.

34

Insulation coordination for wind power plants EMTP-RV Satelite meeting Paris, FRANCE – August 30, 2018 This work has been supported in part by the Croatian Science Foundation under the project “Development of advanced high voltage systems by application of new information and communication technologies” (DAHVAT)