After charging 33kv/11kv transformer vcb not withstandind.

Your power factor to be .9+ and with this improvement vcb will hold.

(sorry i'm not a Electrical guy, this I discussed with my Manager Power)

<our power factor is also not in controll.It is upto 0.66 lagging how we can improve it?>

Add capacitance at the user end of the cable.

80Mohm apply on secondary side winding or to ground resistance?

To improve ur pf is not a problem .Use and automatic pf correction using capacitors.As regds breaker not holding there could be many causes. Is it the breaker odes not hold after switching on 33kv transformer after a lightening strike?

You can also improve your power factor by replacing some of your induction motors with synchronous motors.

Is this breaker on the 440V side? 11KV? 33KV? This may not be a ground fault; it may be a phase-to-phase fault. I would take the affected transformer completely out of service and check everything. You could have a cracked insulator, punctured insulation somewhere inside the transformer, a fault in the wiring between the transformer and the breaker, etc. Check everything, and keep the results of all your tests in a notebook.

The details given by you are not sufficient to trouble shoot.

1) Is it running Plant or new one.

2) Which vcb trips on 33 kV side or 11 KV side.

3) What protections are provided in each of the breakers?

4) When the breaker trips, is it instantaneous or after some time lag.

5) Is there any indication in the protective device about the fault?

I can study your electrical system and suggest suitable measures for improving trouble free operation, provided you send the details if you are interested.