Single loss of phase tests at 33 kV on operating windfarms

The tests presented are a few of those carried out at a number of windfarms in the UK. In the short time and space available the full test procedures have not been detailed. Certain interesting and key tests have been selected for explanation and discussion. All the tests concern wind turbines with induction generators. All the windfarms are connected at 33 kV and use 33 kV/LV transformers at each turbine. LV voltages are 480 or 690 V in different cases. In Example Tests Nos.1-3 the single phasing was achieved by jumpering the PES's outdoor 33 kV circuit breaker on 2 phases at the windfarm substation. The VT to which the protection relays were connected lies on the busbars between the PES breaker and the customer breaker(s). In Example Test No.4 a 33 kV load break air switch was installed in the windfarm cable system, so that the supply to the single transformer and turbine could be broken on one phase whilst the turbine was either stopped or running. A 33 kV/110 V VT was connected on the transformer side of the switch to enable HV voltages to be measured.