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

]

6