how could i decrease residual voltage of 11KV bus that Is created by direct online 9MVA induction Emotor?
Your issue is that the induction motor is acting as a generator, and is taking some time to stop. 

You have a few choices here, you can (if it is acceptable) open the motor breaker before the ATS switches over, cut over to the other bus and then do whatever a normal motor startup looks like once the load has stopped spinning (Brake resistors may help here).

If the two busses are phase synchronous then you could try to make the ATS transfer happen quickly enough that the slip has not become excessive, some sums will be needed to see both how much slip you can accommodate and how long it takes that motor to slip that much once the bus drops off line, the mechanical time constants will matter here. 

You could cut some starting resistance into circuit to limit the current while everything pulls back into sync. 

Lots of ways to skin this, it just depends on what that motor is driving, and can you accept a wait and restart on the motor.