New three phase motor winding burn out

[brizospark]

We have been involved in the installation of a dust extraction system which is powered by a fairly large 3 phase motor (18A).

The motor was pre-wire to a control box on the side of the extraction housing and the star/delta starter was also pre-wired. The only wiring that was required was the 2 sets of cables from the extraction junction box to the star delta starter. These cables were to be connected to the main contactor and the star contactor, anyway we followed the drawing to a t.

The overload was set at 22a and we have used a 32 TP type C MCB at the DB.

The motor was first operated yesterday, it ran for a few hours and then the MCB tripped. I couldn't understand why this would trip before the O/L but anyway it did.

So I had a look at the motor and it was red hot, couldn't even touch it for any period of time so we waited a bit and checked everything, our wiring was spot to drawing and everything in the starter looked ok. I took the cover off the motor when it was cool enough and checked the resistance across the set of windings and one set was Open circuit.

Any ideas what could have caused this apart from a faulty motor?

 

[benji]

Was the o/l conected to main or delta contactor

 

[Knobhead]

So what readings did you get for line and phase current?

Please don’t say you left your test gear at home, in the van, on a hiking trip to Outer Mongolia. I’m in a bad mood as it is.

 

[dazza1981]

So what readings did you get for line and phase current?

Please don’t say you left your test gear at home, in the van, on a hiking trip to Outer Mongolia. I’m in a bad mood as it is.

Its away being calibrated !!!! sorry tony couldnt resist !!!

 

[GLENNSPARK]

So what readings did you get for line and phase current?

Please don’t say you left your test gear at home, in the van, on a hiking trip to Outer Mongolia. I’m in a bad mood as it is.

well i suppose this may help:

 

[Marvo]

What type of motor is it ie is it TEAO, TEFC etc, and what RPM (how many poles)? Does it have an internal thermistor that's interlocked with the Y-D starter? As per Tony's question what were the running currents when you commissioned? Did you check rotation was correct?

 

[brizospark]

Hi, Yes Phase rotation was verified once initially connected. Readings of 1.2Ohms across two of the windings and open circuit on the other. Overload connected to delta contactor. There is no internal thermistor on the motor itself. Can't understand why one of the windings would be burned out. Like previously said we did only have the six connections to make and followed the drawing checked and double checked

 

[brizospark]

Could this just be a faulty motor?

 

[Megavolt]

Bad motor maybe, send it back to get checked over for a refund

 

[brizospark]

I reckon it must be a bad motor as we have followed the drawing and there was nothing complicated about the connections, very straightforward. I have spoken to the manufacturer who asked a few questions about the MCB and overload and they have asked me to obtain a price from a local motor rewinder and to give them a price for repairing the motor to which they will reimburse, all a bit strange really

 

[Sintra]

Personally I wouldn't be happy with that arrangement. If this is a new motor and it is faulty then they should be giving you a replacement.

 

[stef]

Could this just be a faulty motor?

Now it is a faulty motor. Was it rated for star/delta in the first place?

 

[Marvo]

Tell them to get knotted. If you'd wanted a reconditioned motor you could have bought one for half price in the local classifieds. Also how long is the warranty on a rewind and who carries that warranty? Rewinding also sometimes reduces the efficiency of a motor so if the client is on a carbon footprint crusade then they probably won't accept it.

You still didn't give info on the run currents, how close were they to the maximum allowed 18A?

 

[stevethesparks]

Before connecting you new / rewound motor, I'd certainly check why the overload didn't work.

 

[micknew]

Did the starter change from star to delta, if not it would account for your problem.

 

[brizospark]

The starter did change from star to delta I have verified this by running once motor has been disconnected and all works fine voltage checked through ok through contactors and overload.

Regarding the motor being rated for star/delta the extraction unit was all supplied as a kit from a supplier so I can only assume that they would have surely produced a piece of machinery which was compatible with the motor they supplied

 

[stevethesparks]

You need to check that no damage has occurred to the contacts / OL of which may not be apparent with no load connected.

 

[Knobhead]

If it ran for a few hours I very much doubt a faulty motor. What I do suspect is a bad connection/contact in or around the run contactor.

 

[Bobster]

Personally I think it been wired wrong.

As it's changed over to delta, it's ran on 2phases.

 

[Darkwood]

What happened to the old motor ...did it burn out by any chance?