Wind Turbine Generator Self-Excitation once isolated from Grid 1

[BINGMD]

Question: Considering a 34.5kV feeder with dozens of WTGs (wind turbine generators), once the 34.5kV feeder breaker opens, will the WTGs be self-excited and continue energizing the islanded feeder?

My opinion is that, since there will be a sudden active power changes, there will be a large frequencey change, at least frequency elements of WTGs will take theirself down. Voltage elements of WTGs may also take theirself down. It may not happen instaneously due to the voltage ride through ability and the frequency ride through ability.

Appreciate your expertise and any supporting documents.

Will the type of WTG (induction and synchronous) change your answer?

If the 34.5kV feeder breaker opens, what voltage changes will be at each WTG, up, down, no change?

Thank you,
Regards,
Bing

 

[BJC]

I just look at a bunch of wind turbines. The primary generator generated at 575 volts DC. Therre was a solid state invertor in the tower that converted the power to 34.5 KV AC.
The windmill was set up to feather when the load when away. It also had a disk break to stop and lock the shaft. I didn't get a chance to get a good look at the inverter. A 4,350 amps DC in and 34 KV AC out I am sure it was quite sophisticated.

 

[Marmite]

There can be self excitation depending on the capacitance of the power factor correction and the connecting cables. The PFC can be designed so as not to allow self excitation. This resonant condition can give rise to damaging overvoltages. Induction generators can not provide enough fault current to operate overcurrent protection as the current decays after the subtransient phase. For this reason the protection on the main 33kV breaker will be operated by fault current contribution from the network. The wind turbines themselves will start to overspeed once the load is lost and will be shutdown by overfrequency and over/undervoltage protection. Most wind turbines use induction generators. Synchronous generators are not generally used. Amongst other reasons they can cause stability issues on the network due to oscillations as the blades pass through the tower shadow. Induction generators are better at damping these oscillations as they have slip.
Regards
Marmite