Best way to start a 37kw Motor?

[holyhobgoblin]

Hi Folks

Sorry this is not a PLC related question, but been asked to look into installing a Large 37kw Motor and I'm unsure whether to go Variable Speed Drive, Soft-start or Star/Delta starting.

Largest motor I've ever installed is 12kw from memory, i've never used a softstart in my life and always go the VSD route simply because I like the ability to adjust the speed if necessary.

Anyone with some experience with motors this size and best way to start it, your help will greatly be appreciated.

Thanx in advance

 

[Christoff84]

I'd get the pricing on all 3 options, it's a good starting point. Myself, I would say go with a soft-start IF you know you won't need to adjust the speed of the motor, or you don't need the ability to ramp up/down slowly.

If you need the ability to adjust speed, go with the VSD. 50HP is a big motor, but it's certainly not too big.

Remember, with centrifigul fans and pumps, there are significant electrical cost savings to be had by slowing down the fan/pump if you can.

 

[DickDV]

I think you are approaching this from the wrong perspective. You should be focusing on the requirements of the load. If it requires variable speed, then the VFD is the right choice. If it would be physically damaged or if the hard start would upset or cause loss of product and variable speed is not required, then the softstart is required. Also, look at the stopping requirements as a softstart can give you soft stopping as well. This can be beneficial if there is a lot of slack in the mechanicals or if water hammer in a pump when stopping is an issue.

Next, look at your power distribution system. Can it handle starting inrush from a mag starter or even wye-delta starting?

Finally, look at the costs. A wye-delta motor and starter is special and relatively expensive. You can expect a VFD to cost about three times a softstart at 37kw. A softstart on a plain commodity-grade motor will cost about the same as a wye-delta starter and motor.

Everybody loves technology but the right answer here just might be a plain old mag starter and standard motor.

Remember, as always, the load rules everything in motor control systems.

 

[holyhobgoblin]

I think you are approaching this from the wrong perspective. You should be focusing on the requirements of the load. If it requires variable speed, then the VFD is the right choice. If it would be physically damaged or if the hard start would upset or cause loss of product and variable speed is not required, then the softstart is required. Also, look at the stopping requirements as a softstart can give you soft stopping as well. This can be beneficial if there is a lot of slack in the mechanicals or if water hammer in a pump when stopping is an issue.

Next, look at your power distribution system. Can it handle starting inrush from a mag starter or even wye-delta starting?

Finally, look at the costs. A wye-delta motor and starter is special and relatively expensive. You can expect a VFD to cost about three times a softstart at 37kw. A softstart on a plain commodity-grade motor will cost about the same as a wye-delta starter and motor.

Everybody loves technology but the right answer here just might be a plain old mag starter and standard motor.

Remember, as always, the load rules everything in motor control systems.

The motor is to drive a large centrifugal fan which will supply air for a large dryer as well as air for a gas burner. Once the fan starts it will run all day and be turned off once they done for the day.

They have no control of the air flow through the machine so VSD would be the way to go, but as usual money is always the factor these days.

I've decided to quote them for both VSD & Softstart and tell them the pro's & con's and let them decided, if they get it wrong then its not my fault, cover your *** my old boss use to say LOL.

Cheers for the input folks

 

[mendonsy]

I suspect you will find that a VF drive is not all that much more than a soft start and gives you a lot more flexibility.