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100 Hp 480 volt 3 phase pump motor

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ankledeep

ankledeep

Agricultural
Jul 12, 2006
9
Good in electronics and telecom, new to BIG 3 phase motors!!

I have an ag well pump.... 100 Horsepower 480 3 phase "part wind" (6 wire) motor with a "starter" (just 2 big contactors really) one has a phnumatic time delay adjustable from 0 to 40 seconds(as found set to 0.1 seconds)unit is 12 years old. Both contactors have one phase melted open and 2 phases welded shut!!! Haven't meggered the motor yet.... My question: should the 1st contactor close then , 3 or 4 seconds later the 2nd contactor close, (the way the pump on my farm works)or should both contactors close at the same time??? And if the timer was not set correctly, would that have possibly caused the contactors to burn up???? (I found an old contactor in simular burnt up condition laying in the bottom of the control panel!!!)
 
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The purpouse of part winding is to reduce the inrush current. Normally you expect some time delay around 1 to 4 seconds, depending on the load inertia and torque, before the second contactor makes.

 
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Sounds very much like your motor got single phased, as in losing one phase. It stands a big chance of being toasted.

A common contact fryer is a condition where as the contactor closes you get a large inrush which drops the voltage enough to cause the contactor to open which drops the current enough to to let the voltage rise to a point where the contactor can close again.. Of course this happens rapidly until the contactor is toasted or the motor opens or a fuse blows or a breaker opens.

Keith Cress
Flamin Systems, Inc.-
 
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Aolalde's posts are informative. Use them as guide.

Check the motor first. If it is found OK, I suspect the 0.1s timer setting did it, that is contactors were subjected to inrush current in excess of its rating.

From past experience, single phasing seldom affects large motor such as this, specially if its reasonably loaded. But on the other hand pumps have low running torque so never know.

There could be many other suspects:

Did anyone worked on the starter recently? Because a miswiring (bringing two phase together) can do this type of damage.

Was motor running just fine, before the mishap or there was a history of replacing the contacts or the contactors?

Was the 0.1s setting known to exist before?




 
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From what I have learned about part wound motors in the past week plus my own experience with my old ag well pump, contactor number 1 should close (start windings) and pump should start to turn for 3 to 5 seconds then contactor number 2 should close and the motor will speed up to its running speed. I have an experienced pump/electrical person going to test the motor in the morning. I will discuss contactor size and timing with this person.

My bag is really Telecom, 2-way radio, Microwave, Fiber, and SCADA.

I thank you all for your replies!!!!
 
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My posited scenario above could easily occur in a system expecting to have 3 or 4 seconds between contact closure but only getting 0.1s. The two contactors could have been used to avoid too great a voltage drop down a long farm power line.

Good luck!

Keith Cress
Flamin Systems, Inc.-
 
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Thanks, I work for the local Irrigation District (also electric power and domestic water provider for city of 200,000) but no one in the irrigation dept. really knows pumps, the ones that did retired is the last several months!!!!! Kind of a common thing going on around here!!! With the last union contract and retirement enhancments, we lost 10 percent of the work force in the first 6 months of '06!!!! 2 more years til I'm 55.....but not planning on retiring then either....(am I dumb, or what???)
 
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If I wewre to guess (and I am as I type), I'd say this was a 2 transformer open delta system (a.k.a. "V-Phase), very common for remote aggricultural pump systems where the utility didn't want to run all 3 wires a long distance for one load. Nothing wrong with it per se, but IF you get a severe voltage drop, you end up with a severe current imbalance and high voltage on the open phase. I would submit then, along the lines of what itsmoked posted, that someone turned the transition timer too low, which was a virtual across-the-line start, which caused a severe current draw, which caused a severe voltage drop, current imbalance and high voltage on your B phase, which ultimately fried your contactors. It most likely has damaged your motor windings as well.

http:/Eng-Tips: Help for your job, not for your homework Read faq731-376 [pirate]
 
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I have seen similar damage both from fast cycleing and from a short circuit on the load side. The short circuits were either shorted wiring or a burned out motor. The short cycleing was from a badly overloaded generator where the load pulled down the frequency and the voltage until the transfer switch contactor dropped out. Then the generator speeded up and the voltage recovered. The transfer contactor pulled in and the frequency and voltage dropped again. Eventually the contacts burned clear.
respectfully
 
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have you considered replacing that animal with a soft start and be done with it?
JR
 
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