we have steam turbo - alternator of 5 MW, 3.3 KV, .9 PF. 3 month back after emergency shutdown, when we restart the Alternator and just after excitation REVERSE Power relay active, after 45 sec it was manually reset (with out main VCB closing), and Alternator on normal. this event occur after every restart time. are that is actual fault and what is the cause?

 

Hi,

There should not be any actual fault as per my view because there is no question of reverse power without closing breaker. Can you clarify following;

1)Have you tested the relay?

2)Whether this problem was there even before shutdown work? What was the shutdown work?

3)Where the CT input has been taken from?

4)Is it possible to see the data from the relay (fault recorder, events).

Regards
Sunil

 

Hi Mr.Ali,

In your case, there might be problem in speed of the rotor. While starting, if the speed is not enough to maintain the grid frequency, it will take current from the grid and pass it into the alternator to help the machine to keep in synchronous speed. At this case, power will flow from grid to generator i.e., motoring mode. I guess you will be having sufficient "reverse power relay setting" to tolerate this reverse power, that's why you are not facing any trip.

If you take gas turbines, there is no problem of reverse power. Because, we have Static frequency converter to help the machine to attain its synchronous speed before connecting to the grid.If you post the exact history of events and reverse power relay settings...i will be able to give you the better solution than this....