Can standard electric motor be coupled with VFD? or VFD requires special inverter duty motor?

Hi,
VFD requires an inverter duty motor. A standard Motor is derated.

Can you please elaborate?

when in doubt, always check the motors manual. The manufacturing company should have there technical information about the motor (nominal rpm, nominal voltage etc) and if you can couple the specific motor with a VFD.

An inverter duty motor can deal with the higher voltage spikes produced by VFDs also can run at very slow speeds without overheating. The general purpose motor don´t, it can overheat if it is running too slowly, so bearings and insulation will be damaged

Standard motors can be used with VFD's to a ratio of 4:1.
Inverter duty motors go up to a ratio 10:1.
Check your variable speed curve since at a certain low speed, you will not pump at all (no head). Hence, in some cases, you will not need an inverter duty motor.

Nowadays, motor manufacturers are standardizing their motors to inverter duty or some call it VFD compatible.

Hello Patrick

Do you really mean 10:1 ratio without burning. If the motor last for 5 years without burning.

This can be very big break-through in rotating pump industry. Most rotary pump working with 4 pole motor. Within the ratio of 10:1 to 2:1. But only question remains, will they provide the required torque. This can reduce the cost of reduction drive.

Hello Bhalchandra,
For the 10:1 ratio, I was referring to centrifugal pumps where torque is variable. When speed decreases, the torque load decreases to the square of the speed and the HP to the cube of the speed. Therefore the temperature rise factor is none. Always size up your motor to the worse case scenario at 100% speed, then speed down.

PD pump is different to centrifugal. They are constant torque loads. Therefore, when the speed changes, the torque load remain constant but the HP has a linear change with the speed. Thus, PD pumps draw high AMP rating at low speed as compared to centrifugal. Heat will increase. In this case, motor manufacturer need to know that you are in a constant load application and they will provide the proper temperature rise motor. May be not 10:1 turn down ... .

Most larger motors are VFD compatible, if the speed control is for speed reduction only. Speed step-up would require inverter duty motor. It is best to check with motor supplier.