SKS

You can only protect the load that is beyond the circuit breaker.

Example - Hydro Generator is 100 feet from breaker.

Transformer is 100 feet from breaker.

Generator to Transformer distance is 200 feet.

Only 100 feet is protected - past the breaker to the transformer.

The reason is this - even you shut off the breaker, the generator side is still energized. You cannot protect the wire coming from the generator unless you put the breaker closer to the generator.

Move the breaker closer to the generator to protect more of the wire between the breaker and the transformer - Generator to breaker 25 feet. Breaker to Transformer 175 feet. More wire on the load side is protected.

This has nothing to do with switching of the exciter circuits or the magnets in the generator, or stopping generator rotation, that would stop voltage in wire between generator and circuit breaker.

I based pune city in india countery,

my office a mnc and used ups system in office.

one day our office light current off and ups current are on and when main current return in office light than circuit breaker not working properly and ups system are blast and our office inside some fire.

so used carefully circuit breaker.

Generator on rent

Have you considered asking your supervisors in this hypothetical hydro power plant?

If they exist they will explain the system used.

thanks, i was considering if reacatance of cb should be considered.

regards,

sks

IEEE C37.010-1999 "Application Guide for AC High-Voltage Circuit Breakers Rated on a Symetrical Current Basis" gives information on adjustment of the current interrupting rating of high voltage circuit breakers when the X/R ratio is higher than the standard value (I believe it's X/R=17 for 60Hz). See particularly section 6.3.

You might also want to check out IEEE C37.04-1999 regarding asymmetrical current ratings.