Flashover in new motor

[nraju]

We installed a new ABB-make induction motor just 3 days back. The motor details are 460V, 60 Hz, 179 kW, 278 amperes, 1787 rpm.We did the usual commissioning checks. Winding resistance was found balanced and IR value was 500 Mega Ohms. Yesterday, the motor got flashed over. The motor was very hot and smoke was observed when the terminal box cover was removed. When we checked the IR value, it was 0.02 mega ohms.
This motor was installed to replace another motor which was to be sent to the workshop due to abnormal sound. Both the motors are exactly same as far as details are concerned. The earlier motor was running for more than 5 years and hence, no changes in the relay settings had been made ever since it was commissioned.
We are totally perplexed as to the reasons of the failure of this motor. Any help as towards the possible causes for the flashover of the new motor would be appreciated. The motor is in a covered shed while the MCC is in an air conditioned dust-free room.

 

[panelman]

If you checked all the obvious things you might have to fall back on "sometimes new things fail...it's called infant mortality" and call ABB

 

[DanDel]

Have a motor shop check it out and determine the cause of failure(overheating/overload, or pinpoint insulation failure).
500Mohms is not that good of a reading, especially for a new motor. What voltage were you using?

 

[GusD]

Hi nraju

Your new motor ran for 3 days and aparently burned up.

What kind of motor protections do you have?Are your O/Loads set properlly?
Is it a VFD application?
What type of load is it?Crusher,Belt Conv,Pump ?
I guess you would like to have answers, rather than questions.It is hard to speculate on the problem without some background information.

You meggered the motor and it read 500 MOhms ,which is good.Being a brand new motor, you could have used a Megger up to 1900 V.What Voltage did you use to Megger the motor?

If the motor is Insulation Class B and 80 Deg Temp Rise,
the temperature of the windings shoud not have exceeded 130Deg.High ambient temperature would reduce your allowable temp rise.

Are there any winding thermal protectors?

If the phases are severelly umbalanced it would give rise to Neg,Seq,Torques that can overheat motors beyond their design.Without more details on your particular conditions it is hard to narrow it to a single problem.

Get info from the repair shop as to what do they think caused the failure.

Good Luck
it could







GusD

 

[jbartos]

Suggestion: Considering that the old motor experienced abnormal sound (abnormal sounds are often attributed to high harmonic contents), the new motor could malfunction because of a possible high harmonic content in the voltage of the power supply. The power supply should be checked for the acceptable power quality, e.g. less than 5% of voltage total harmonic distortion (THD).