Motor for VSD

[singpower]

Hi
Presently, there are few set of pumps(motors) started by softstarters. Due to the changes of application, we need to use VSD instead of softstarter. The contractor explained that motor also need to be replaced as current motor(s) is not suitable for the VSD.
My question here is that is it correct fixed speed motor can not be used as variable speed motor?
I am supposed to ask motor supplier/manufacturer but I would like to hear from other opinion.

Regards

 

[waross]

A VFD assaults a motor with a lot of high frequency high voltage transients. A VFD rated motor has an insulation system designed to withstand the high voltage trensients.
The difference is not "Will it Work?", it's "How Long Will it Work?"
With pumps be aware of forbiden speed ranges. As each vane of an impellor passes the discharge it sends a pressure pulse down the pipe. These pressure pulses can reflect back from an elbow. At certain speeds, the reflected pulses add to the new pulses. This can be cumulative and actually burst a pump casing. A good quality VFD for pump duty will have provision to lock out certain speeds or frequencies.
Baldor Electric suggests that for some applications a non VFD rated motor may be used.
I would suggest calling a reputable motor rewind shop for an evaluation of your needs. At the same time query the feasibility of having some of your existing motors rewound to VFD standards.
yours

 

[itsmoked]

Adding to waross' good points many people run standard motors with VFDs with no problem. I am running a non VFD motor for its 11th year with a VFD. So if your motors are a pain to change or have little reserve value you could just punt and VFD them.


Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[singpower]

Thank you, waross and itsmoked for your valuable inputs and quick response.

Regards

 

[CJCPE]

The severity of voltage transients at the motor is related to the length of the power cable between VFD and motor. With a very short cable, there may not be a problem. A higher VFD switching frequency may be more of a problem than a low switching frequency. Check with the VFD supplier for specific recommendations. VFD suppliers can also recommend output filter solutions for the voltage transient problem.

 

[ozmosis]

Your AC supply is very important to know. If, for example, you are on a supply >500Vac then using a VFD will certainly need consideration on the type of motor used.

 

[jraef]

And conversely, if you are running 240V or less, it is unlikely that you will need to worry about that motor.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[AllanUK]

Are the pump-sets located in a hazardous area? If so is it zone 1 or zone 2? This would have to be considered if changing the motors from fixed to variable speed.

As a minimum for variable speed motors in hazardous areas, motor thermistors would need to be connected in order to directly trip the motor on high temperature. Shielded power cable would also be required.

If a zone 1 area, I think that the motor and VSD has to have been certified as a system (ATEX) - i.e. the motor/drive combination will have been tested and approved as a system by the certification body (BASEEFA or equivalent).

Allan

 

[singpower]

Hi AllanUK,
Thank you for your inputs. However Pumps are located at non-hazardous area.

Regards

 

[Magdrive]

FYI you might like to take a look a more motor friendly VSD at

http://WWW.payback.com

Tim Macdonald
Hydro Dyne Inc.