Soft Start Torque Limiter

[dave1pm]

I am a mechanical engineer with limited electrical knowledge so please exscuse any part of this question that may be simple or incorrect.

I have an ATEX rated geared motor unit driving a slow speed vessel agitator. I was planning to use a frequency inverter to set a torque limit but have now found the motor is not inverter rated for Ex applications.

My question is, would it be possible to use a soft start as the torque limiter instead of a frequency iverter?

 

[dpc]

The soft starter is used only during starting - it can certainly limit torque during that brief acceleration period. Normally, the soft starter is switched out the circuit for normal running operation and has no effect on torque or anything else.

If your concern is only for torque during starting, the soft starter might work depending on how severe the torque limitations are.

David Castor

http://www.cvoes.com

 

[LionelHutz]

No, not during motor running.

 

[DickDV]

You might want to check with the motor manufacturer to see if the motor can be relabeled for Ex and Inverter Power. Some can. They send you a new nameplate. You attach it to the motor and now the inverter can be added.

 

[edison123]

Even if your motor is not originally rated for VFD duty, you can get it rewound to VFD duty with rewinders having Ex certification.

Muthu

http://www.edison.co.in

 

[Marke]

Hello dave1pm

There is a product called a shaft power monitor that can be used to act like a shear pin.
See

http://www.emotron.se/en/products/Shaft-power-monitors/Emotron-M20/

This technology is also built in to the MSF soft starter at the same website. This will cause a trip if the set torque is reached rather than limit the actual torque produced.

Best regards,
Mark.

Mark Empson
L M Photonics Ltd

 

[dave1pm]

Thanks for all the replies.

We have now changed the motor ordered to an Ex rated for the VFD, this meant a small increase in power from 6.8 to 7.5kW, but no major problems.

Thanks Again.
David