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14 comments
Participant

Join Date: Apr 2012
Posts: 4

Overheating of Induction Motor

04/17/2012 2:36 PM

dear all,,

I need your idea, I have 6 motors, each motor is 5hp, 440-480v 60hz in 1 machine.. this 4 motors are connected to the frequency inverter and i check the output voltage for this inverter is 480vac and the hz setting is 60hz. and the other 2 motors are connected direct to line 480Vac which is getting high temperature. why this 2 motors are getting high temperature?

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#1

Re: overheating of induction motor

04/17/2012 3:28 PM

So the ones that are NOT connected to the VFDs are the ones that are getting hot?

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#6
In reply to #1

Re: overheating of induction motor

04/18/2012 1:17 PM

yes,,the two motors that are not connected to VFD are getting high. why this two motors which is not connected to the VFD are getting high temperature compare to the 4 motors which is connected to the VFD? this all motors are same rated in the nameplate and same load also.

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#2

Re: overheating of induction motor

04/17/2012 4:27 PM

It may be that the two direct-connected motors have a higher mechanical load than the four VFD-driven ones. Can you tell if the two motors are simply hotter than the others, versus actually hot enough to worry about damage?

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#3

Re: overheating of induction motor

04/17/2012 10:33 PM

check if your motor connections matches the nameplate voltage, possibly it may be in delta instead of star vice versa.

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#4

Re: overheating of induction motor

04/18/2012 12:20 AM

Check What is the load connected to these 2 motors. High temperature means how much?

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#7
In reply to #4

Re: overheating of induction motor

04/18/2012 1:30 PM

The load of this 2 motors are same to the 4 motors which is connected to the VFD. And base in the nameplate the maximum temperature of this 2 motors is 40 degrees centigrade. And now the actual temperature of this 2 motors is 50.

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#8
In reply to #7

Re: overheating of induction motor

04/18/2012 2:17 PM

If I had to guess (and I do have to because I am not there), I'd say that you likely have a voltage imbalance on your incoming supply lines and the VFD couldn't care less because all it does is rectify it to DC. So because the VFD is recreating its own new output to the motors, it is balanced. But the motors NOT connected to the VFD are going to be affected by a voltage imbalance. Even a small imbalance or 1 or 2% causes unnecessary heating in AC motors.

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#10
In reply to #8

Re: overheating of induction motor

04/18/2012 5:49 PM

I'll bet a GA to you that's that problem lumberjack man, hope the OP gets back on it

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#9
In reply to #7

Re: overheating of induction motor

04/18/2012 4:23 PM

I suspect your terminology is incorrect. Motors are more often rated for temperature rise above ambient, rather than an absolute limit like 40°C (104°F), which is not very hot at all.

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#11
In reply to #9

Re: overheating of induction motor

04/18/2012 6:05 PM

Good catch, I missed that detail in his post. Common misconception too. I get a lot of people aiming their new IR gun toys at motors and saying "It's too hot!" when in fact it's way under the maximum temperature rise.

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#13
In reply to #11

Re: overheating of induction motor

04/19/2012 1:05 AM

Thank you, its good to know that.I guess you will need fans on motors even if the ambient temperature is below 0 deg. C.

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#14
In reply to #7

Re: overheating of induction motor

04/20/2012 12:21 AM

How come 40 deg centigrade and 50 deg centigrade are high temperatures??? Its ambient temperature and motors have to function normal at these temperatures.

And as for my knowledge, the supply frequency from direct line may be greater than 60 Hz. (say +5%). This frequency rise can increase hysteresis loss and eddy current loss in the motor which can rise the temperature of motor.

sharath

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#5

Re: overheating of induction motor

04/18/2012 3:03 AM

Check the trip setting of the overload protection device in each motor circuit and make sure that the full-load-current rating on the motor data plate is not exceeded by the trip setting.

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#12

Re: Overheating of Induction Motor

04/19/2012 12:23 AM

Do a Megger test on all 4 motors.

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