I was performing power factor test in a wind farm. During the test, 20% of turbines experienced converter faults due to voltage spikes. At the end of the test, all the turbines continuous to operate with no errors. I checked SCADA data and notice that voltages spikes was in the range requested by the turbines/Converter manufactures. I need you to help me understand what really happened.
The test consist to provide a power factor equal to 0.95 capacitive at the point of interconnection and hold it for at least 30 minutes. We sometimes used a bank of capacitors to provide reactive power to the entire farm when it is necessary. But it wasn't necessary for the test. However, we demanded additional power from some turbines via The Power Management Unit (PMU).
Capacitors are reactive power generetors which give rise to voltage generation like in the case of Ferranti effect. That may be the reason for voltage spikes.
I have two questions:
1- What are the types of your generators? Self-excited Induction or synchronous generators?
2- where do you apply the capacitors for power-factor correction? At the load terminals?
I think that if you use a capacitor which results in a capacitive power factor of 0.95, the self-excited induction generator will build a terminal voltage clearly higher than the rated voltage which will harm the semiconductor converters resulting in faults.
The Generator we have on our turbines is a DFIG. And the Capacitor Bank was apply at the substation level. Spikes occurs at the PADMONT , converter side.
Oh, then it is not self-excited IG! These generators are tied to the power grid through substations. Is this true?
Yes it is true. Turbines are group through a collector network at a substation also called Feeder. Then, Feeder are tied to the power Grid. DFIG is a Doubly Fed Induction Generator.
I know the DFIG, now which Pf you are correcting? is it the Pf of the current supplied to the substation?
To be frank I am lost. However my instinct tells if you reduce the kVAr rating of the capacitor bank the voltage spikes can be avoided.
This condition is not easy. The IG output current is normally leading the voltage which means it consumes reactive power. When DFIG is used you can control the output current from the stator side to be in phase with the voltage, or even lagging the voltage. My question is: what is the purpose of using capacitor bank? do you use it as a local VAR generator to feed the IG with the required VAR? In this case, be sure not to use excessive reactive power as this will increase the generator terminal voltage, and may damage the converters.
I can explain this by attached diagrams if it is needed.
I will appreciate M. Mohammed. However, thanks you all for your answers
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