Aug 30, 2018 - transformers (step-up and power transformer) ... Evaluate voltage protection margins ..... Example 3 â 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
5
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
8
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.
12
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
16
Restrike phenomena during breaking of small inductive current
17
Restrikes caused by VCB switching
„ELECTRICAL TRANSIENT INTERACTION BETWEEN TRANSFORMERS AND THE POWER SYSTEM”, CIGRE WG A2/C4.39
18
Example 2 – Failure of power transformer 110/25 kV
Failure of 25 kV winding
19
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
26
Damages caused by direct lightning strike
27
Lightning and surge protection for the wind turbine
28
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)