Electric Automation Forum
Forum » Variable frequency drive » Can standard electric motor be coupled with VFD?
Topics: Can standard electric motor be coupled with VFD? on Variable frequency drive
#1
Start by
bhalchandra padwal
01-14-2014 09:00 PM

Can standard electric motor be coupled with VFD?

Can standard electric motor be coupled with VFD? or VFD requires special inverter duty motor?
01-14-2014 11:25 PM
Top #2
Sashang Balasubramanian
01-14-2014 11:25 PM
Hi,
VFD requires an inverter duty motor. A standard Motor is derated.
01-15-2014 02:11 AM
Top #3
bhalchandra padwal
01-15-2014 02:11 AM
Can you please elaborate?
01-15-2014 04:43 AM
Top #4
Konstantinos Pylarinos
01-15-2014 04:43 AM
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.
01-15-2014 06:53 AM
Top #5
Jesús Rivas
01-15-2014 06:53 AM
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
01-15-2014 09:47 AM
Top #6
Patrick Li
01-15-2014 09:47 AM
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.
01-15-2014 12:41 PM
Top #7
Patrick Li
01-15-2014 12:41 PM
Nowadays, motor manufacturers are standardizing their motors to inverter duty or some call it VFD compatible.
01-15-2014 02:58 PM
Top #8
bhalchandra padwal
01-15-2014 02:58 PM
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.
01-15-2014 05:06 PM
Top #9
Patrick Li
01-15-2014 05:06 PM
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 ... .
01-15-2014 07:20 PM
Top #10
Ratnakar Mankad
01-15-2014 07:20 PM
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.
Reply to Thread