Electric network faults seen by a wind farm – analysis of measurement data Sanna Uski, Seppo Hänninen, Bettina Lemström

2 Measurement site x Olos Helsinki Measurements - 2,5 sec 500 Hz - 0,33 sec 3,7 kHz - triggered by U0 Ur, Us, Ut Ir, Is, It, U0 5x600 kW Ur, Us, Ut Ir, Is, It t Measurement at Olos wind farm on 21 kV level t 5 x 600 kW fixed speed wind turbines t Turbines equipped with – squirrel cage induction generator – capacitor bank – Dyn step-up transformer t Connected to relatively weak 21 kV grid (S k ~50MVA) t 21 kV grid reactance grounded

3 Voltage dip distribution t Voltage dips detected in 196 cases out of 260 t Several dips involved in one incident, 5.4 dips in average (max 36) t Multiple types of faults, 3 phase, single phase etc. Residual voltage Dip duration No. of dips

4 Voltage dip examples; Two phase faultAutoextinguished earth fault t 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 t Autoextinguished earth fault – Caused by thunder – Three voltage dips – 28…34 ms, Ures 0.44, 0.74 and 0.85 pu

5 Varying faults t Most of the faults are varying – fault resistance – fault type t 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 t Available in Annex database

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