Generally the motor with Class F insulation is considered as VFD graded motor, but it is specified that the dV/dT withstand capacity is 1 KV/μS. Hence we can not consider this motor as VFD graded motor.
1. The standard IEC60034-17 clearly defines the admissible dV/dT levels for motor to be used with variable frequency drive. Hence the motors, which complies the dV/dT as per this standard only will be considered as VFD graded motor. The permissible limits are indicated in below picture


2. Also the standard NEMA MG 1-2011, Part 31, specifies that insulation systems to use with VFD in low-voltage (≤ 600 V) inverter-duty motors should be designed to withstand an upper limit of 3.1 times the motor's rated line-to-line voltage. This is equivalent to an upper limit of 1413 V peak volts at the motor terminals for a motor rated at 456V (415+10%). Rise times must equal or exceed 0.1 microseconds.

3. The customer has mentioned that the peak voltage withstand capacity is 1 KV/μS, which is much lesser than the limit mentioned in above standards. Hennce the motor can not be used with VFD with the standard cable length provided in the catalog.

4. If you need to use the motor with VFD, it is mandatory to use motor choke or sinus filter to reduce the dV/dT and peak voltage at motor terminal, the picture below will provide the dV/dT limit with motor choke.


As per the above information, the dV/dT will be limited to 1 KV/μS and the peak voltage will be 1000V with motor choke. Hence the motor will work without any problem by providing a choke in the output of the VFD.

Diterbitkan untuk: Schneider Electric Indonesia