Calculation of a ACB or VCB for a AC Generator

Before calculation of a LT/HT breaker you should take care all large machines in a power plant are rated in KVA. So keep this in mind.

Example :- 

Give a specification of a LT (415 Volt) breaker  for a 2000 KVA Alternator.
For any designing in electrical machines we need to get full load current of a machine, then add the percentage of safety factor & other factor too.

Generator Power = 2000 Kva

                P= 1.7321V*I 

             Now Current will be = 2000*1000/415*1.7321 Volt  
                                               = 2782 Ampere 
Now breaker selection will add different safety factors in ratting, with short circuit current. I don't know the exact method for selection of a breaker. but here we used 3200 Ampere because of nearest Breaker in ratting is 3200 Ampere with SF.

Same method you can also apply for transformers too for current calculation in primary & secondary side.

Thanks,
Anuj Tyagi