A client with a 34 MW generator is having repeated exciter bearing failures. However, the vibration levels remain steady & the spectrum does not indicate any degradation.

While taking some power measurements, we noticed that the power factor varies between 5-13 % over 1 minute. I vaguely remember someone from Baker telling me that power factor variation (or was it torque ripple) was an indicator of torsional vibration. Has anyone any information on this?

Regards,

Aditya

It must have been the torque ripple.
If the generator is synchronized with a large power system (many generators), then the power factor variation are caused by the variation in the excitation current. The generator then supplies reactive power to the system depending on the excitation.
The case when the generator works by itself will be very different. The power factor is governed by the load. And if the reactive power requirement in this small system varies, so does the power factor of your generator.
jank