I have an MG set .i.e. A dc motor coupled to an 3-ph, 5kVA Alternator. when it is subjected to a non linear load like A 3-ph fully controlled rectifier SCR bridge it is not giving the required waveform, but the same 3-ph FCR Bridge connected to grid supply it is performing well. will you please trace out reason and give the remedy.

 

The reason is fairly easy, a 5kVA alternator doesn't resemble house power. Most of the problems are probably because it's source impedance is much higher than the grid. It can't supply anywhere near the instantaneous current that SCR controls often pass at low conduction angles to maintain a given average current. So the generator output waveform will go south and that makes phase controls unhappy. Heavy filtering might help, but it would have to be tuned. The real solution is a low Z source or a less demanding load.

Regards,
cww