Hello Amit,

Its hard to guess the exact number of seats provide by PSU's as they don't have constant vacancy evry year.In this year if they take 20 than next year they might not take a single candidate also.

But i will let you know some of the companies average intake according to previous stat's.

NBCC 15-30

NTPC-10-15

ONGC 10-15

HPCC 15-20

IOCL 15-20

Power grid 10-20

NHAI  14-20

There are some more psu,on totaling all the seats there are 200-300 steats.But i may differ different year.

Hope it will help