Induction Motor Tripping: On Same Load One Trips While Other Does Not

Was this a used motor (the one that was failing) or a new motor?

This motor was in use since 2007. from previous month, this situation happens. No issue of overload device.

Are there predictive maintenance program like motor winding temperature data gathering daily? What is the NEMA rating of the coils? Life expectancy to certain type of winding coils at corresponding temperature is about 20,000 hrs.

check overload device

I suspect that the windings of your used motor are well worn. That is to say that with a full load, the additional heating is enough to break down the insulation somewhere in the tightly wound coils. It is usually less expensive to have the motor rebuilt (or rewound) with new wire than to buy a new one. Always make sure that the cooling system is open and not clogged with dust. Excess heat is not your friend.

Dear Friend,

It appears from your statement that you have checked the Stator only but not the Electrical Condition and Mechanical Condition of the Rotor. namely bend in the shaft, Bearing condition etc. You have not stated whether the the motor is of Slip-Ring Type or Squirrel Cage type.

The problem of tripping may be:

1. From Mechanical Aspect such as Bent Rotor Shaft, problems in the Bearing, causing heavy friction by damaged roller/ball causing severe resistance for rolling. There by starting current is very high and trips.

2. From Electrical Aspect - Defective Rotor - no continuity in the rotor circuit, damage in the squirrel cage rotor namely loose end of the rotor, change in the magnetic character of the rotor, very large air-gap than required between the rotor and stator etc.

Pl. check for the above items and inform us what was the problem, and how solved.

DHAYANANDHAN.S

Motor is squirrel cage induction motor.

Last month it was tripped on phase un-balance. when we check, we found that connection plate inside the terminal box was broken. change the terminal strip.

Motor is connected to the gear unit via fluid coupling. cooling fan is O.K.

The stator may have sustained damage due to single phasing, but then who am I to say anything, I shall relegate my postings to "Caption this" blog.

You have not stated what amps are for original or replacement motor when loaded.

Like many post info given is incomplete or just not given. You would think some one took the time to check no load current would also check the current under load. The statement as one trips the overload the other doesn't is poor info to define a problem.

All this could be caused by some one spilling something sticky on the belt. The extra friction caused by the sticky substance. That is on the back of the belt. Under load could just be enough friction to have the old motor draw just enough amps to trip the over load. The new motor could be running just under the threshold need to trip the overload. I seen this problem in the grocery industry where damaged container leaked on the belt.

Then he says he puts a load on it. The same load? Uniform over the length of the belt.

There are over mechanical problems with the conveyor which could also cause this.

To say that your motor is running at "no load" when it is in fact driving a conveyor negates all the rest of your information.

What does the nameplate say the no load, and full load amp draw should be?

What NEMA class is your motor?

There's too much you don't know!

If the fact that a smaller motor is driving your conveyor without a problem should tell even you where the problem lies.

Get the motor looked at by a competent service person. Yes, that will cost you money.

There are multiple possibilities.

The stator and/or rotor laminations have been damaged. (Shorted due to insulation failure, shorted due to physical damage of the rotor dragging on the stator laminations surface caused by motor bearing failure.)

The rotor laminations shorting rings have been damaged or are broken/open causing loss of magnetic flux and decreased HP/torque.

The rotor is not running in true magnetic center of the stator. (Run the motor uncoupled and scribe the shaft next to the bearing then couple the motor and verify the shaft is maintaining magnetic center while operating under load.)

The motor windings are incorrect. (Wrong conductor size, wrong span, wrong number of coils, wrong number of turns in each or one or multiple wing coils.

There are one or more shorted turns in the motor winding that are not discernible with a VOM and require a motor analyzer for identification.

If the motor has been rewound more than three (3) times, the laminations are highly suspect.

I recommend you send the motor to a reputable motor winding shop for evaluation, and ask for test results as well as recommendations for possible rewinding.

I would insist on a warranty from the motor winding shop before spending any monies for repair and/or rewinding.