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200hp motor burns contactor
3

200hp motor burns contactor

200hp motor burns contactor

(OP)
200 hp 3 phase 2speed motor burning up high speed size 5 contactor. Low speed draws 64 amps/high speed amps 223 when running correctly. Motor has been rebuilt. Time delay between low speed and high speed. aprox 30 sec. shows aprox 3-4% voltage drop at MCC contactor can, motor is another 85 ft away. Cutler-hammer contactor vibrates when pulled in. (more than normal) Burns (a phase) when going to high speed, contact point melted. Replaced contactor three times, with new size 5 cutler-hammer style.
Same problem occurs about every 5 to 6 weeks. Where else should I be looking?
 

RE: 200hp motor burns contactor

Look for something causing chatter.  It would only take a second or two of it to toast the contactor.

  Perhaps the control voltage dipping from something.  As frequent as it is occurring you should immediately get a recorder going on the control voltage across the contactor coil.  You will likely see something immediately if not sooner.

Keith Cress
kcress - http://www.flaminsystems.com

RE: 200hp motor burns contactor

What is the 200hp motor driving, if I may ask? Melting of contacts may indicate that the contactor is closing on very large current here. I see you said 233A running at high speed, that's about your motor FLA; recommend upping the contactor to say size 6.
If the contactor is at the MCC and not near the motor, you can rule-out voltage dip, IMO.

RE: 200hp motor burns contactor

Are you replacing the contacts or the whole contactor? Have you checked the voltage at the coil? A broken shading coil will cause a contactor to growl but that is very rare. More common is corrosion or mechanical damage to the mating surfaces of the core. My personal favorite was a contactor where a burned out coil was removed with the help of a large hammer on the face of the iron core. But, this doesn't often cause contact problems. The hammer damaged contactor has been working well for several years now, even if it is noisy. If this is a DC operated contactor look for a blown diode. Check the coil voltage as per itsmoked's post.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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