Distributed Generation problem

[paddyB]

Problem:
Alternator Rotor winding failure (Turn to turn.) only on 400volt machines in parallel with grid. Not on high voltage machines on same installation. (Rotor construction identical.)
Site conditions:
Very weak grid, with lots of loss of mains.
Lots of power factor correction. (Capacitive.)
Lots of underexcitation trips due to power factor being in the unstable zone, presumably after loss of mains.
Rotor winding is protected by a varister. (No failures.)
Failure could be caused by induced voltage from surges in stator?? (AC on DC circuit???)
Any ideas or suggestions as to why only LV machines?

 

[TheBlacksmith]

LV machines may have less reserve on the insulation (thinner/lower rated) and be more susceptible to surges. If you have a system/program to monitor the insulation you may want to check the higher voltage machines, you may be doing culmulative damage and they will eventually fail.

Blacksmith