Short Circuit Current

All three phases shorted at once?

Yes, All 3 Phases shorted together.

The specs says' the generator should be capable to deliver the 3 times short circuit current for 3 seconds'

That's why, then. If it couldn't then something is undersized.

quote "The specs says' the generator should be capable to deliver the 3 times short circuit current for 3 seconds"

3 time what short circuit? What value are you using?

the generator rated current is 100 amp, Specs says that it should deliver 3 x 100 amp when all the three phases are short circuited.

Dear Visham Lele,

Refer to ANSI C50.13-1977 the generator should able to deliver current as below:

Sec 10 30 60 120

I armature (%) 226 154 130 116

If your spec state 3 times full load amperes when all three phases short-circuited.

It may be difficulties for generator manufcaturer to decide subtrasient reactance to generate shart-circuit current 3 times full load amps. Please check again your spec.

As pen ANSI above, The generator should able to be loaded for 226% FLA for 10 seconds. It make sense that 3 times FLA for 3 seconds.

Regards,

I have now the recent update from Marine Agnecies.

As per the specs the Generator should be able to deliver the 3 times the Full load current when all 3 phases of the Generator to descriminate the fault.

The Explanation is -

When the Short circuit Fault occures in any equipment connected to the generator, the generator will see the phases short circuited & the terminal voltage of the generator's shorted phases would be ZERO. at this moment the Automatic Voltage regulator will see no voltage at the terminals. If the AVR's power is being fed through the Terminals of the alternator , the AVR will fail to work. Resulting tripping of the Circuit breaker at the generator end.

Now if your Generator has the above capability ( to supply the power to the short circuit) the Short Circuit fault in the equipment will be fed untill the Equipments protective relays tripps. In this case the Fault Descrimination will be easy.

I feel this is what I understood talking to different Marine Agencies.

Please correct me if I am wrong....

There is incorrect language being used in the specs, or in someone's repetition or interpretation of them.

It would make sense for a generator to be able to deliver briefly 3 x rated current, such as for starting motors, but it is impossible for it to deliver more than the short-circuit current, because that is all even a short circuit will draw.

The generator will "brown out" before that happens, anyway. Ain't fun to watch....