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Electric network faults seen by a wind farm – analysis of measurement data
Sanna Uski, Seppo Hänninen, Bettina Lemström
2
Measurement sitex Olos
Helsinki
Measurements- 2,5 sec 500 Hz- 0,33 sec 3,7 kHz- triggered by U0
Ur, Us, UtIr, Is, It, U0Ir, Is, It, U0
5x600 kW
Ur, Us, UtIr, Is, It
Measurement at Olos wind farm on 21 kV level
5 x 600 kW fixed speed wind turbines
Turbines equipped with– squirrel cage induction
generator– capacitor bank– Dyn step-up transformer
Connected to relatively weak 21 kV grid (Sk~50MVA)
21 kV grid reactance grounded
3
Voltage dip distribution Voltage dips detected in 196 cases out of 260 Several dips involved in one incident, 5.4 dips in average (max 36) Multiple types of faults, 3 phase, single phase etc.
Ures 0.01
…0.
1 s
0.1…
0.25
s
0.25
…0.
5 s
0.5…
s
sum
80…90% 405 33 5 0 44370…80% 183 7 3 0 19360…70% 178 5 1 0 18450…60% 77 6 4 0 8740…50% 95 2 1 0 9830…40% 39 4 0 1 4420…30% 1 1 0 0 210…20% 0 0 0 0 01…10% 0 0 1 1 2
sum 978 58 15 2 1053
Residual voltageD
ip d
urat
ion
No.
of
dips
4
Voltage dip examples;Two phase fault Autoextinguished earth fault
Two phase short-circuit– Triggered at fault clearing
caused a change in neutral voltage
– Residual voltage 0.6 pu– Duration of the dip 258 ms
0.5 1 1.5 2
-20
-10
0
10
20
U p
h [
kV
]
0.5 1 1.5 20.4
0.5
0.6
0.7
0.8
0.9
1
Urm
s [
kV
]0 0.5 1 1.5 2 2.5
0.5
0.6
0.7
0.8
0.9
1
1.1
Urm
s [
pu
]
Autoextinguished earth fault– Caused by thunder – Three voltage dips– 28…34 ms, Ures 0.44,
0.74 and 0.85 pu
5
Varying faults
Most of the faults are varying– fault resistance– fault type
Example case;– starts with two phase short circuit– changes to two phase-to-ground
fault– and to a three phase short circuit– fault cleared, earth capasitance
discharge causes multiple short voltage dips
Available in Annex database
0.5 1 1.5 2
-20
-10
0
10
20
U p
h [
kV
]
0.5 1 1.5 2-1
-0.5
0
0.5
1x 10
4
Uo
[V
]
0.5 1 1.5 20.5
0.6
0.7
0.8
0.9
1
Urm
s [
pu
]