3 Phase motor uncoupled load current exceed nameplate rating 2

[biggeorgetechnical]

I have a situation with a brand new 1/2HP 3Phase 230/460Vac TEFC motor. (Baldor M3538 frame 56 1725RPM class B etc.)

I installed the motor, wired up the terminals for 460VAC - double and triple checked them in fact.
This little motor is running hot, in fact it is getting so hot that it prompted me to measure the phase currents with a clamp ammmeter. I was surprised to see the no load current exceding the nameplate current by about 15% (1.15A) where nameplate is 1A. This was the same on each phase.
Our 460Vac bus at the plant is running high right now - about 485Vac.

In my experience, no-load currents never exceed nameplate - what have others experienced?

 

[motorsdirect]

Hi,
what is the rated frequency on the plate?? and how is this corresponding to the voltages.
Also, overvolting will raise the current quite dramaticaly...would be nice to try running this at its rated voltage!!!
have you also made sure that the motor is connected properly for your voltage too??? should be y (star) connected!!
jeff

http://www.motors-direct.co.uk

 

[busbar]

On the North American continent, utilities and utilization-equipment producers generally agree on the numbers in ANSI Std C84.1-1995 table 1. The listed upper limit for 480 nominal-system voltage and 460 nominal-utilization voltage is 504 or 508 volts. No doubt the motor voltages and currents have been verified as reasonably balanced?

 

[buzzp]

Is the shaft uncoupled entirely? Perhaps what you think is no-load may indeed have a load, ie bad bearings on the new motor (not likely) or bad bearings/couplings on the device connected to the shaft.

Other than the higher voltage, I do not see any reason it should be this high. What does Baldor say about this?

 

[biggeorgetechnical]

Re motor:
Here are the measurements, obviously not perfect, but within reason. We are running 60hz in response to motorsdirect.

V 1-2 = 488Vac
V 2-3 = 488Vac
V 3-1 = 486Vac
I 1 = 1.04A
I 2 = 1.10A
I 3 = 1.04A

When I say hot, the motor surface temperature is in excess of 60C within an hour at no load. Our plant ambient right now is less than 30C. I know we would expect such a gross overheating if the wiring was done incorrectly, but this has been checked and doublechecked by two other resident experts.

I really have no way of lowering the bus voltage to 460Vac, and other three phase motors are behaving as expected. Any chance Baldor could have the leads mismarked or the wrong nameplate information?

 

[motorsdirect]

sounds like.....as long as it is connected star....that the wiring must be right , otherwise,there would be a much bigger differential in the phase currents.
I was wondering if the motor is wound for 60hz...I would assume that it is being Baldor....
Also,,what is this driving,,and what is off load???
jeff

http://www.motors-direct.co.uk

 

[biggeorgetechnical]

The motor nameplate says 60Hz. I called the local baldor service center, they said run it for an additional hour and report back to them. He stated they have plenty of them available for warranty replacement.

The motor at this time, is completly uncoupled. Would be driving a small clutch and flywheel if I had not noticed the excessive heating before connecting it... Guess thats what I get for taking the recommended action of a 1 hour uncoupled run before loading.

 

[motorsdirect]

It doesnt sound like a faulty motor, unless the winding data is completely wrong..as the phases are balanced!
can you not test run the motor elsewhere on a true 460v?, just to prove a point.
I have had plenty of experience of 415v rated 50hz motors running over current on 440-445v!!! especially poorly made and designed foreign,mainly eastern bloc motors.
jeff

http://www.motors-direct.co.uk

 

[busbar]

If leads were mislabeled on a plain-vanilla NEMA 9-lead stator, it would quickly be apparent with very poor operation... like emitting smoke or at least significant current imbalance.

 

[aolalde]

I have the manufacturer (Baldor) reported Test Performance Data for motor M3538.

The No-load current reported is 0.8 Amperes. at 460 Volts.
The PF at 25% load is .30, Eff=.532, line current=0.8 amps
The PF at 50% load is .43, Eff=.664, line current=0.85 amps
The PF at 75% load is .55, Eff=.725, line current=0.92 amps
The PF at 100% load is .63, Eff=.746, line current=1.03 amps

The temperature rise over ambient is 65°C at full load, for 30°C ambient, the windings reach 95°C with 1/2HP load.

The over voltage could cause saturation and then drop of the motor the power factor, increasing the no load current from 0.8 to 1.06 average. Per NEMA MG1 standards, that motor must withstand operation up to +10% of nominal voltage (506 Volts) but certainly the parameters like current could change from those in the nominal nameplate parameters.

 

[biggeorgetechnical]

Thanks all,

I will take the necessary steps to obtain a true 460Vac and report the results. We did at one time have a three phase variac set here, which I could use to apply the nameplate voltage. Perhaps Baldor eliminated so much iron from this little motor design that the 10% allowed voltage range is too optimistic. The way things are right now, with the smoky smell emanating from the windings after 1 hour, I am willing to try anything.

George

 

[Skogsgurra]

biggeorgetechnical,

I wouldn't be too alarmed. These little motors usually have rather bad power factors, even at nominal voltage. I have seen P.F. down to 0.6 and that means that the magnetizing current is larger than the torque-producing current. In the actual case, it would mean 0.8 A magnetizing current and when running at higher voltage it will be even more. So the idling current will be high.

Also, a thirty degrees increase in temperature is what you should expect when running with this kind of current. Sixty degrees is very hot to the touch, but not really hot for a class F motor (which I assume that it is, if it is a modern motor).

I think that you should couple your load and run the motor. Measure the current and measure the surface temperature. Or even better; measure winding resistance when cold and after running for an hour. Calculate temperature rise from resistance change. I think that you will be pleasantly surprised.

If you have access to an Osanna (Heyland) diagram, you can see how this works. And if you read the motor current when loading the motor gradually you might see how the current drops when you start to load the motor. It then gradually increases as load increases. Sounds like a paradox, but it is true.

 

[Skogsgurra]

Aoalde's numbers (we seem to have been typing at the same time) support the assuption that the P.F. is very low.

You say in your last posting that there is a smell emanating from the motor. I cannot understand how that can be if your surface temperature is 60 centigrades. Smoke takes a lot more heat to develop.

 

[biggeorgetechnical]

The findings:
1) Located three phase variac, set it up to apply 455Vac, connected it to motor.
2) Measured no-load phase currents, they now agree strongly with Aolaldes Baldor spec sheet, and the data supplied to me by my conversation with Baldor field service office. (.8A@no-load on all three phases)
3) Smell, this little motor design is only class B, internally was clearly exceeding 60C+ by a significant margin. Did not measure the resistance drop, but I have used that technique in the past sucesfully. There is no longer a detectable smell.
4)Regarding coupling it up to the load, I now feel confident that I will be successful and not suffer a short service life. The excessive heating in this case took me by surprise, having dealt more often with much larger, relatively more efficient motor designs.

Thanks to all!

 

[motorsdirect]

Glad you got it sorted....thought as much....too much skimping on materials these days brings tolerences right down, and in instances like this...the motors work way too hard......but Baldor!!! I am suprised!!
jeff

http://www.motors-direct.co.uk

 

[Skogsgurra]

Another interesting case that we all learned from. Thanks for the feed-back.

 

[KKmack]

You may want to have a spare motor nearby. Your overheating motor w/no load may have a problem with the rotor, possibly an open or defective bar in the squirrel cage winding. Or, there could be another magnetic defect. If the rotor is defective, an induction motor can do strange things, including overheat/overcurrent at no load.
I would take your Baldor distributor's offer to swap out this motor. When you get it, test this other motor with no load. It would be interesting if this motor has the same problem.
Good luck, and let us know if you find anything else.

 

[DickDV]

If 485 volts is too high for this motor then the manufacturer is playing way to close to the edge with the design. 485 volts in the areas where I work (USA, upper midwest) is far more common than 460 volts.

I would be a bit upset with the manufacturer with a situation like this. Surely, a Marathon or Reliance motor would be expected to behave thermally at 485 or even 495 volts.

 

[buzzp]

I guess this is a sign of things to come from our manufacturers.