1° motor overheats at 1/2 FLA on full voltage

[nelsonhoover]

What is going on when a single phase 240V electric motor running at 1/2 of full load amps, overheats and trips out?

All connections are fine, I'm getting 233 volts directly at the motor. There is no voltage drop across any breakers or contactors. We've tried a new motor with the same results.

Could something such as utility power factor be messing with me? This motor is located a good distance out in the country, away from any sub stations.

Thanks for any ideas on this.

 

[MikeHalloran]

Is it running at full speed?
With adequate ventilation?
How many wires come out of the motor shell to be terminated?
Have you double checked those connections? Not for tightness; for the right wires tied to each other, etc.





Mike Halloran
Pembroke Pines, FL, USA

 

[edison123]

Is the cooling fan fixed to the motor ? Have you cross-checked the load current with another meter ?

Muthu

http://www.edison.co.in

 

[itsmoked]

What exactly trips out? Motors don't normally have any way to trip out.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Start winding left in circuit would likely cause the overheating. Kinda depends on what variety of single phase motor it is. Are there one or more cylindrical objects clamped to the stator casing?

Can't blame the utility for this one, it's something on either the motor or controlgear.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[MIK2000]

single phase motors always warm-up it it is running at the load that less than their full power. So you get it work at 1/2 load this is i mean.

 

[nelsonhoover]

OK, it's a 10 HP Leeson Farm Duty motor. These have a built in Klixon overload button. The previous motor on this application did the same thing as the current motor, which is a new motor.

The amperage was checked with a Fluke 189 with an inductive amp clamp. It has not given me any crazy readings before so shouldn't be the problem. And yes, the motor is running full speed and has a cooling fan, etc. Also, it is wired correctly. It is powered with #6 copper (which buy the way, doesn't even get the slightest bit warm). FLA on the motor is 40 and according to my meter is currently pulling around 18. (It's on an auger, so we where able to run it at half load by just trickling the grain into it). The voltage directly at the motor terminals is 233V.

Start winding does kick out after start up and the capacitors are 100% OK, ScottyUK (I've seen what happens when it doesn't, more than once. Lots of motor growl and if not stopped - bang - there go the start capacitors). I run a small motor repair shop out in the country and have never run into anything like this. Is there something I'm missing here?

There are a few other motors hooked to the same service and the customer was complaining that they occasionally trip out as well. None of the breakers are getting warm or have any voltage drop either.

 

[edison123]

May be it's your OL protection that's gone south.

Muthu

http://www.edison.co.in

 

[Marke]

I have found this before where the V/Hz was incorrect. USA made motor operating on 50 Hz. Name p[late was changed by the manufacturer to read 230V 50 Hz but the windings were not. Motor marked 50Hz but wound 60Hz.

Best regards,
Mark.

Mark Empson
L M Photonics Ltd

 

[itsmoked]

Hi Marke! Wouldn't that result in high current?

The OP states that his meter is reading 1/2 the FLA.

Since other motors are having this issue too, I'm going to suggest that there are some nasty harmonics out at the end of this country line that the Fluke is not seeing but is there heating the motors up.

It could even be some sort of DC current that the meter is not going to see.

nelsonhoover; I would stick an oscilloscope across the motor leads and see the whole picture. Do be sure the scope can be hooked safely to mains though!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

I think Keith is on the right track. Line harmonics can indeed affect a temperature rise in a single phase motor that will not show up in a current based model. Here is a white paper on the subject. I'd post an excerpt from it that addresses this specifically, but the text is copy protected on the pdf. The paragraph I think points to this scenario is on the lower left of [page 2, starting with "Core..."

The only other possibility I can think of is that you have a severe coupling or journal bearing heating problem, and the heat is traveling back on the motor shaft to affect the Klixon. But typically, the Klixons are at the NDE of the motor, so the heat would have to travel a long way to get there. I find that difficult to fathom.


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[MikeHalloran]

You didn't give us the nameplate info.
I found a connection diagram for _A_ Leeson 10HP farm duty motor.

It shows two run windings in parallel. The ends of both are marked T1 and T4, and should be tied together, T1-T1 to terminal 3 of the protector, and T4-T4 tied to the line and T5 or T8 depending on the direction.

If that's your motor, the symptoms suggest that one of those windings is not connected. Couldn't happen for two motors, though...




Mike Halloran
Pembroke Pines, FL, USA

 

[nelsonhoover]

Marke, I measure the hertz (along with everything else my Fluke would do) and it's spot on 60, which is correct for these motors.

MikeHalloran, it is wired correctly.

itsmoked and jraef, It's about got to be something like that. I'll try to come up with a scope and see what I find.

 

[electricpete]

my vote would be gremlins. Double check everything you've told us.

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[waross]

Grain dust may be plugging up the internal cooling passages.
If you are moving a particularly dusty grain it won't take long even with a new motor.

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

 

[Marke]

Are you measuring the current going into the motor, or are there power factor correction capacitors connected between where you are measuring and the motor.
If you are measuring motor current plus power factor correction current, then you could easily overload the motor without realizing it.

Best regards,
Mark

Mark Empson
L M Photonics Ltd

 

[MikeHalloran]

It's time to put the amp-clamp on _every_ wire.
Something that we know to be true, clearly isn't.


Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

If you give us the Leeson number we can look up the motor and see what you have.
How dusty is the environment? Obstructed cooling paths will explain your overheating at below full load current.

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

 

[flandrax]

I don't feel that you have a ventilation problem. Correct me if I'm wrong, but the Klixon overload is located on the side of a large terminal box. If a ventilation problem was causing the Klixon trip, the motor case would have to transfer heat to the terminal box and so on....In my opinion the motor would burn up before the Klixon would be able to trip. Just some scenaros I've seen in the past "trash", stems, cobb, straw, will overload the motor.