3Ph, 1.5HP Inductor Motor Running at Low Speed 1

[sykimk]

Hello,

As a part of startup process, we did motor run but the speed is quite lower than the rated speed. Please refer to the following information.

Rating: 1.5HP, 3PH, 460V, 2.1A, 60Hz, 1760 RPM, SF=1.15
But motor running at 1558 rpm and 1.5Amp. So, I don't think it is overloaded at all. But I don't understand how this motor ran at 1588 rpm (88.5% of rated rpm). Mechanical folks told all flow and pressure are OK while runnig this motor.

Can you please advise why the acutal motor speed is way lower than the rated speed? It this motor's rotor OK with operating at this lower speed than the rated speed?

Thanks for any advices/tips in advance.

Power

 

[electricpete]

I was told that tachometer was good condition and used for other mootors as well.

Then I'm inclined to agree with Lionel, maybe it is just a case of running in wye when should be delta. Then the effective voltage is sqrt(3) lower so the entire torque curve is about a factor of 3 lower and the lowered motor torque-speed curve might intersect the load torque-speed curve at a speed far below rated nameplate speed. Granted our first reaction is typically that a motor in that condition should draw higher currents... but I'm not positive about that. We expect the load component to go up but we expect the no-load / magnetizing component to go down, and in small motors the no-load component can be a lot larger than the load component.


Or perhaps as che12345 suggested we should check the current balance. It might perhaps create a similar reduced torque and inability to accclerate to rated speed... and if you are only monitoring one of 3 phases currents then by luck it might be the lowest of the three phase currents.

Now I'm thinking about a motor supply that does not match motor nameplate 60hz. I don't think the motor would operate above 1500rpm if you supplied 50hz. But... is there perhaps a vfd associated with this motor?

It this motor's rotor OK with operating at this lower speed than the rated speed?

It's an abnormal condition that we haven't explained. I think we need to reserve judgement about specific conclusions like this until we understand the more general big picture explanation for the low speed.


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(2B)+(2B)' ?

 

[edison123]

20 to 30 bucks.

Muthu

http://www.edison.co.in

 

[sykimk]

To all of community member,

I really apprecaite your adivces/tips and I didn't expect such large group attention to my post. Anyway so sorry for late update but we couldn't run the motor due to some other process issues.
For a bit more information, this is the lube oil pump and direct coupled with motor. So, we cannot uncouple it. One more is this is the DOL motor no VFD driven motor.

We ran this motor yesterday and still had same issue (low operating speed ~ 1560 rpm yesterday). So, we immediately stopped the motor and strongly claimed it was overloaded by something in pump/process side. Therefore, our mechanical folks checked their side again and again. Eventually found oil level was very higher than normal level. After they brought this oil level down to normal range, the 2nd motor ran looked good (rpm ~ 1755) now.

Really appreciate all of your feedbacks. . Frankly, I am happy this wasn't electrical issue.

 

[electricpete]

OP - Thanks for the feedback (LPS). Many people ask questions but don't bother to report back what they find.

But it still does leave a question about the current. Assuming this is an induction motor with proper supplied frequency and voltage and connections, then we'd expect that a mechanical overload which caused the speed to be lower than nameplate would also cause the current to be higher than nameplate.

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(2B)+(2B)' ?