3 phase induction motor troubleshooting

[Abhi]

I have 3 phase motor of rating 3 kw, rpm=960, flc=6.5amp, volt=415v, resistance= 3.5ohm

I was performing polarity test of winding, so i applied 230v ac supply to one of its winding. But the motor started and running with low rpm and afterwards smoke came out of its winding. I switched off the power supply immediately.

Connections for the polarity test was absolutely correct. So nothing wrong there.

Then I connected motor in delta connection and current was 53amp and again I changed it to star connection and now current was 5.5amp.

There is nothing wrong in measured values provided by me. So there should be no doubt about it. I shared here what I experienced.

So my question is why this happened and does motor runs during polarity test.

 

[Besoeker]

I have 3 phase motor of rating 3 kw, rpm=960, flc=6.5amp, volt=415v, resistance= 3.5ohm

I was performing polarity test of winding, so i applied 230v ac supply to one of its winding. But the motor started and running with low rpm and afterwards smoke came out of its winding. I switched off the power supply immediately.

Connections for the polarity test was absolutely correct. So nothing wrong there.

Then I connected motor in delta connection and current was 53amp and again I changed it to star connection and now current was 5.5amp.

There is nothing wrong in measured values provided by me. So there should be no doubt about it. I shared here what I experienced.

So my question is why this happened and does motor runs during polarity test.

Some motors will run when single-phased, your 230V test, but not very well. Connecting it in delta if it is wound for star would saturate it hence the high current and smoke.

As a matter of interest, why were you doing a polarity check anyway?

 

[Abhi]

Some motors will run when single-phased, your 230V test, but not very well. Connecting it in delta if it is wound for star would saturate it hence the high current and smoke.

As a matter of interest, why were you doing a polarity check anyway?

Bcoz in star connection and in unload condition the motor is taking high current about 5.5 amp and its flc is 6.5amp. it should take less than 3 amp. Thats why i thought of polarity test

 

[Besoeker]

Bcoz in star connection and in unload condition the motor is taking high current about 5.5 amp and its flc is 6.5amp. it should take less than 3 amp. Thats why i thought of polarity test

How does it perform when loaded?

 

[just the cowboy]

Slower motor

Slower motor

From what I remember a slower motor 1200 RMP will run higher unload than a higher RPM 1800 -3600 due to the slip not as great due to the speed.

 

[Abhi]

How does it perform when loaded?

It takes around 8 amp in load condition which is higher than flc(6.5amp)

But i cant understand how motor started running when i applied 220 vac to its only one winding( i.e. U1 and U2) and other winding ends were opened.

 

[Besoeker]

It takes around 8 amp in load condition which is higher than flc(6.5amp)

But i cant understand how motor started running when i applied 220 vac to its only one winding( i.e. U1 and U2) and other winding ends were opened.

Three phase motors can and do run when you have a lost phase. The protection is usually in place to detect that and shut down.

 

[Abhi]

Three phase motors can and do run when you have a lost phase. The protection is usually in place to detect that and shut down.

Ok
Then tell me how to do polarity test for a 6 lead 3 phase induction motor( squirrel cage)

 

[Besoeker]

Ok
Then tell me how to do polarity test for a 6 lead 3 phase induction motor( squirrel cage)

Never needed to.

 

[GoldDigger]

Could a shorted turn in one of the "open" windings have created a shaded pole motor effect, causing both the rotation and the high current?
Shorted turns are generally not detectable with DC measurements.

Sent from my XT1585 using Tapatalk

 

[Abhi]

Could a shorted turn in one of the "open" windings have created a shaded pole motor effect, causing both the rotation and the high current?
Shorted turns are generally not detectable with DC measurements.

Sent from my XT1585 using Tapatalk

May be I agree to your point

 

[Besoeker]

Could a shorted turn in one of the "open" windings have created a shaded pole motor effect, causing both the rotation and the high current?
Shorted turns are generally not detectable with DC measurements.

Sent from my XT1585 using Tapatalk

At 3kW I'd just replace it.

 

[just the cowboy]

Did you turn the shaft

Did you turn the shaft

Did you turn the shaft by hand and it started with voltage on one winding?