VOLTAGE& FREQUENCY FLUCTUATIONS ON A1MVA GENSET

[ah1989]

dear all
we have a 1000kva, 400v diesel generator , made by a japaniees company [ nippon sharyo ] and powered by a 16 cylinder v type mitsubishi engine , this set is fully protected by a 24v dc relay board and a complet set of analoge sensors, transducers,meters, the above combinations are functioning very well .
recently we had a strange malfunction which is that the main 1600amp breaker suddenly is tripped [ not overload neither sc.]we are at less than 20% load, the voltage on the meter is fluctuating between 100 to 400v, the frequency 45 to 52 hz the engine in ths case is running on normal speed, which suggests no mechanical error, we wait for about 10-15 min till the fluctuations are gone,so the voltage & frequency readings are normal again,then we push the close buttom and the generator is servicing again normally, this malfunction happens irregularly[ once a week, once aday]with no indecation on the alarm panel at all
any similar practise, suggestions will be greatlly appreciated, thanks

 

[18pulse]

The rpm seems alright (45 to 52 Hz, if your nominal frequency is 50Hz). I would suspect your have problem with your AVR, as the voltage varied from 100 to 400V. 100V means almost no magnetising! If I were you, I would check the magnetising circuit first.

 

[waross]

I would check the Automatic Voltage Regulator as 18pulse suggests.
Unlike a tachometer which will dependably indicate speed, some frequency meters are somewhat voltage dependant. Your speed may be varying or speed may be steady and the frequency meter is responding to low voltage.
You may have an intermitant fault in your field circuit.
Try installing both a voltmeter and an ammeter in the output of the AVR.
If the current rises when the voltage drops you have an intermitent fault in your field circuit.
If the current drops when the voltage drops, change the AVR.
respectfully