We have Siemens 6.6 KV feeder for high voltage motor. For motor KW less than 1 MW Siemens has provided surge arrester in Motor feeder. It is not provided for motor above 1 MW rating. What is the reason ?

Practices and opinions on use of surge protection vary and there is no single right answer for what applications require surge protection and which don't.

Motor surge protection is more often applied on larger, higher voltage motors, and more critical motors.
Motor surge protection is more likely required if the motor supply includes a vacuum circuit breaker or vacuum contactor.
Motor surge protection is more likely required if the motor is fed from a long run of cable.
Ratio of cable impedance to motor impedance is also a factor when long runs of cable are present. Low ratio more likely requires protection.
Motor surge supression is more likely required if surge suppression is not provided at the entrance to the facility (usually is provided)

Motor surge protection is less likely required if special requirements are invoked on motor
turn insulation (dedicated turn insulation) or surge testing (3.5pu vs 2.0 pu).

Motor surge protection is preferably provided at the motor terminals. However, I have recently learned that in some circumstances some people apparently allow to put surge arresters on load side of circuit breaker.

This message has been edited. Last edited by: electricpete,

Many thanks for your explaination.