Whar is over fluxing & how it is worked? is it very hearmful to a Transformer?

What will be the set value of over fluxing relay of a 2 X 10MW captive power plant, having 2nos of 12.5MVA, 33/11KV transformer and both are running in synchronised condition with grid.

 

Sarkar, responding to your questions in the order they were asked:

1. Overfluxing of a transformer occurs when its flux density exceeds rated density.

2. It is caused when its V/f ratio is greater than that which the manufacture deems is safe. This, of course, is the case when it is connected directly to the generator, i.e., without benefit of an intervening circuit-breaker, and the generator’s excitation system is energized while accelerating to operating speed!

3. Yes it is harmful. The effect is to produce a disproportionate increase in magnetizing-current and excessive iron-losses.

4. Of course, there are tolerable limits. But, the set-value for the relay should be supplied by the manufacturer!

Regards,
Phil Corso ([email protected])