Motor Start and stop cycles

[pknol]

We have three vacuume systems 7.5 hp, 25 hp and 15 hp. They only need to run when work is running. Is there some rule of thumb that if required in x min don't turn off the power? How long will a motor last in continuous operation vs start and stop operation? If a start and stop operation is more cost effective will the cost of putting in a soft start system pay for itself.

 

[dpc]

How often do they start and how long do they run?

 

[itsmoked]

There are definite 'number of starts per hour" ratings on all motors whether stated or not.

A soft starter won't save you much money. They are a big help preventing voltage sags in other local circuits. I believe they save nothing in regard to frequent starting. They heat the motor the same amount on each start, and they reduce the mechanical shock to rotor parts and the driven equipment.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[electricpete]

http://www.joliet-equipment.com/allowable_starts.htm

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[pknol]

The motors could 40min per hour 24 hours per day. They would also be shut down 30 min at three lunch periods.

 

[jraef]

That's considered very light duty for an AC induction motor. As Keith said, the only benefit to using soft starters on this application will be in reducing mechanical stress on the other power train equipment from repeated starting.

One thing to consider though (if possible or not already in place), is to tie the 3 vacuum systems together and write a simple little PLC program to monitor the real vacuum required, based on what is operating that needs vacuum. Then sequence only the amount of HP that is necessary at any given moment. I have done this twice with dust collection systems and it saved a lot of energy. I used soft starters only because the blowers were 150 - 300HP; we ended up turning the blowers on and off more often than they used to, so the soft starters alleviated the mechanical issues that arose from that.

Were I to do it again, I would now use VFDs to fine tune the vacuum HP consumption.

JRaef.com
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