motor failure 2

[humbleuser]

I don't hang out in this forum anywhere near enough as I should. This is great technical site. However, I do have a question that I'm hoping some of the more experienced mebers can answer. Keep in mind that I'm not a trained electrician; I'm more of general maintenace type of guy

I have 25 HP G.E. motor (230/460 3-phase) attached to an injection molding machine. I saw this machine running and making parts prior to me buying it. The place where it came from had it wired for 460. I brought it and rewired it for 230. The motor ran for about 5 minutes, somewhat noisy, before it started smoking and tripped the breaker. The shop that is rewiring it told me that I had the proper wire connections to the motro. I asked him what caused it to burn out? He's not sure. He says the bearings aren't in bad shape. he thinks that some of the 'varnish coating' on the windings may have worn out. It's possible that some condensation on the worn area may have caused the motor to short out. Is this possible? Thanks in advance.

 

[electricpete]

At 230 volts, the motor has to draw roughly twice as much current to provide the same output load. That will cause increased heating of the motor which likely damaged the windings.

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[humbleuser]

but shouldn't the windings be able to withstand the additional heating from the lower voltage since the motor is designed to run at, either, 230V or 460V? Do you think the windings were on the verge of going bad and the lower voltage was "the straw that broke the camel's back"?

 

[itsmoked]

Moisture probably takes out half of all motors. Otherwise your load it too great. You simply MUST check the current on the three phases of your running motor. They 'shall' be less than the name plate FLA. If not that is most likely what killed your motor and will shortly kill your next one.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Condensation will kill a new motor quickly. It will kill an old motor with borderline insulation even quicker. If condensation is an ongoing problem, instal a strip heater to keep the motor frame warm when the motor is not running.
Arrange the controls to turn the heater off when the motor starts.
respectfully

 

[edison123]

I would also look at whether the winding was wired right for 230 V. I would guess it would be delta connected.

* If a little knowledge is dangerous, then I am the safest person in the world *

 

[davidbeach]

edison123, a standard NEMA dual voltage motor is wye connected for both voltages. There are two windings for each phase. In the higher voltage connection the two windings are in series while in the lower voltage connection the two windings are in parallel. (note the 2:1 relationship between the two voltages) Changing from 460V to 230V would double the current, but you now have two windings in parallel, so the current in each winding shouldn't change. On the other hand, if you had one of the windings paralleled with a different phase the smoke would definitely come out.

 

[Skogsgurra]

If the rewirerers are quick to point out that it was correctly rewired, then it probably wasn't. You should examine the connections and compare to the diagram that (perhaps) is on the inside of the connection box cover.

If the rewirerer bet you to it, you can be almost certain that there was a mistake.

On the other hand, if current wasn't checked, it is very probable that the motor was overloaded. The high noise level indicates that. What setting the protection/fuses?

Gunnar Englund

http://www.gke.org

 

[edison123]

davidbeach,

I agree. It could be double wye connection.

* If a little knowledge is dangerous, then I am the safest person in the world *

 

[suriae]

When a motor is installed, either old or new, common practice is to measure the insulation resistance before switching on the power to ensure the condition of the winding. Skogsgurra is correct that it is wrong connected to double Y.

 

[electricpete]

Sorry, I misread the question. Thought you simply applied 480vac motor on reduced voltage. Please disregard my comments.

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[petronila]

Hello Humbleuser,

If the motor start with noise this is an indication of mechanical troubles: Improper fits or bearing damage or electrical problems: improper winding connection or Single phase operation.I think due to the motor works only 5 minutes the failure was produced by single phase operation.

Check the breaker and contactors in order to find some problem with the electrical instalation.

Regards

Petronila

 

[jraef]

What seems to be missed in a number of responses here is that the motor worked fine when he observed it prior to moving the machine. That means it is not mis-sized and barring a mechanical problem that developed during the move, not overloaded. The moisture issue may have played a part, but how long was it off-line and how much moisture was it subjected to?

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[aolalde]

If "The motor ran for about 5 minutes, somewhat noisy". It probably was wrong connected.

 

[humbleuser]

The motor was working fine for the 1/2 hour that I saw it running prior to me buying the machine; it was running under 460 power. I forgot to mention in my original post that the face plate doesn't show the lower/higher connections. It's possible that I misconnected the leads (I had 4-5-6, 1-7-L1, 2-8-L2, 3-9-L3). I didn't check to see how the leads were connected for the previous higher voltage (shame on me). The motor sat for about a month before I connected it. The only other info I have on the motor/pump is that the pump had been recently rebuilt. I can turn the pump by hand. I'm wondering if the motor wasn't bad to begin with which is what caused the pump to go bad. I just don't know.

 

[l3city]

humbleuser:

how about re-sizing overload fuses, disconnect & wiring? Remember that the voltage changed from 460V to 230V.

 

[humbleuser]

The breaker that is currently in the machine is 100A. If anything, I'll need a higher rating breaker to handle the lower voltage/higher amp draw. Keep in mind that the breaker never tripped.

Initially, I thought for sure that I miswired the connections. The repair shop insists that I had it wired correctly. They're also telling me that the bearings are not that bad of shape. They think that moisture caused it to short out. The noise that it made before going 'kapoot' has me baffled. Was that noise normal or not? I simply don't know because I'm not familiar with the machine when it's running. When I inspected the machine it was running but it was too noisy in the shop to really notice anything unusual. I'm stumped.

 

[aolalde]

The connection you describe is correct for 230 Volts if the motor worked on 1 wye at 460 Volts, but what if some of the terminal mark labels were improperly attached?
However, the noise could have developed due to unbalanced magnetic field because of initial tracking to ground of one phase.

 

[jraef]

Improper fuse size would not make the motor smoke!

Those would be the proper connections for a Y-connected dual voltage 9 lead NEMA motor, which constitutes what GE sells as standard. If by chance it was a dual voltage Delta-connected 9 lead motor then those would be wrong, but I haven't seen one of those in years. Is it an old machine?

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Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[humbleuser]

The machine is a 1989 model.