Inverter duty motors 2

[rcook]

I am trying to confirm if there is a code requirement that an inverter duty motor is required when installing a VFD. It is an existing condition. The client is looking to add VFDs to existing motors, but does not want to change the motors.

 

[Tmoose]

Some motors from before the VFD era are actually VFD compliant, according to a few case-by-case inquiries I've made to manufacturers.

Details like voltage rating of insulation, mechanical support of windings, and potential for speed increases are among what determine VFD suitability.

 

[micalbrch]

I'm not aware of any standard which requires that. If your client does not have an internal standard he must follow, I'll guess he is fine with what he is planning. It depends a little bit upon the motor size in combination with the power that is drawn by the machine. If you have a 90 HP motor and the required power is only 50 HP, it will work well even at low speed. I assume your question is not related to an explosion proof motor?

 

[dvd]

Be careful about slowing a non-VFD rated motor too much: the motor cooling on a slowly rotating motor relies upon radiation from the motor housing since the fan is not moving enough air to cool the motor with forced convection. VFD rated motors typically have a larger frame size. If you want 2:1 speed range on the motors it is significantly different than 1000:1 speed range. Make sure that the VFD control panel interface will not allow damaging slow speeds. Conversely speeding up the motors past the synchronous speed may result in the inability of the motor to provide sufficient torque. Talk to your motor's manufacturer about specifics.