Bridgeport Three Phase Motor Troubleshooting

[Artfrombama]

Greetings!
I have a older Bridgeport vertical mill (3 phase wired low voltage) that I have powered by a VFD. I went out to finish a job yesterday morning and the motor won't start. I first suspected the Chinese VFD but I want to check the motor before I order another VFD.
Confused as to how to "ohm out" the motor because it has nine leads. Can anyone help a bro out?

 

[micromind]

First unsplice all the leads them ohm each one to the motor frame. All should be infinite resistance (open circuit).

Next, look at resistance from 1 to 4. It should be very close to 2 to 5 and 3 to 6.

7 to 8, 8 to 9 and 9 to 7 should be the same but close to double the other readings.

This is not a complete thorough test but if it fails, the motor is shot.

 

[wyliesdiesels]

have you confirmed with a multimeter that the VFD is outputting power?

 

[Artfrombama]

have you confirmed with a multimeter that the VFD is outputting power?

Yes, all three

First unsplice all the leads them ohm each one to the motor frame. All should be infinite resistance (open circuit).

Next, look at resistance from 1 to 4. It should be very close to 2 to 5 and 3 to 6.

7 to 8, 8 to 9 and 9 to 7 should be the same but close to double the other readings.

This is not a complete thorough test but if it fails, the motor is shot.

1-4=Open, no resistance
2-5=233.5 Ohms
3-6=3.8
7-8=6.8
8-9=7
9-7=7
#4 to frame=.4ohms

Smoked

 

[Innovate1]

Running motors from VFDs is hard on insulation due to the fast edges of the output. They make motors with better insulation that are rated for inverters. They also make output filters but I haven't seen those used much. Not saying that is what caused the problem but it could be.

 

[mm08822]

Running motors from VFDs is hard on insulation due to the fast edges of the output. They make motors with better insulation that are rated for inverters. They also make output filters but I haven't seen those used much. Not saying that is what caused the problem but it could be.

Based on the apparent age of the motor, I would say that the vfd is the cause of insulation puncture.

If rewinding this motor, make sure to mention vfd driven.

 

[wyliesdiesels]

Yes, all three

1-4=Open, no resistance
2-5=233.5 Ohms
3-6=3.8
7-8=6.8
8-9=7
9-7=7
#4 to frame=.4ohms

Smoked

yeah you let the magic smoke out.... one winding burnt open and shorted to the frame... another is almost fried....

 

[wyliesdiesels]

Running motors from VFDs is hard on insulation due to the fast edges of the output. They make motors with better insulation that are rated for inverters. They also make output filters but I haven't seen those used much. Not saying that is what caused the problem but it could be.

definitely get a VFD rated motor for the replacement

 

[whateg01]

definitely get a VFD rated motor for the replacement

Usually specified as "inverter duty", or something like that

 

[Ag 85]

The motor was originally nameplate rated for 460 volt not 480 Volt which is now seen in modern distribution and or VFD.
I have worked with motors rated for 440 Volts wound in 1930's. Higher torque output but longevity is reduced at higher than rated voltage. Inverter duty rated they are not. Nore info here.

What Is an Inverter Duty Rated Motor?

Over years of use in the motor industry, the term “inverter duty” for motor ratings has become watered down. Whenever someone refers to an inverter duty motor, they are usually referring to a higher insulation class for the windings.

www.pumpsandsystems.com

A good rewind shop can make that motor new and inverter duty. Then it fits and looks original.
Good luck.

 

[wyliesdiesels]

The motor was originally nameplate rated for 460 volt not 480 Volt which is now seen in modern distribution and or VFD.
I have worked with motors rated for 440 Volts wound in 1930's. Higher torque output but longevity is reduced at higher than rated voltage. Inverter duty rated they are not. Nore info here.

What Is an Inverter Duty Rated Motor?

Over years of use in the motor industry, the term “inverter duty” for motor ratings has become watered down. Whenever someone refers to an inverter duty motor, they are usually referring to a higher insulation class for the windings.

www.pumpsandsystems.com

A good rewind shop can make that motor new and inverter duty. Then it fits and looks original.
Good luck.

probably cheaper to buy used...

 

[micromind]

Yes, all three

1-4=Open, no resistance
2-5=233.5 Ohms
3-6=3.8
7-8=6.8
8-9=7
9-7=7
#4 to frame=.4ohms

Smoked

No question, the motor is cooked.

 

[kngelv]

I can’t tell if that‘s a delta or wye motor. Use a megger. These are for low voltage. If a delta put these pairs together 6-7, 4-8, 5-9 and leave 1, 2 and 3 apart. These are your L1, L2 and L3. Check 1,2 and 3 to ground. Should be over 100 megaohms. Will still be ok over 10 megaohms. Phase to phase should be low ohms. If open you have broken windings. Do the check with a wye. Jump 4,5, and 6 together. Your L1, L2 and L3 are 1-7, 2-8 and 3-9.

James

 

[mm08822]

I can’t tell if that‘s a delta or wye motor. Use a megger. These are for low voltage. If a delta put these pairs together 6-7, 4-8, 5-9 and leave 1, 2 and 3 apart. These are your L1, L2 and L3. Check 1,2 and 3 to ground. Should be over 100 megaohms. Will still be ok over 10 megaohms. Phase to phase should be low ohms. If open you have broken windings. Do the check with a wye. Jump 4,5, and 6 together. Your L1, L2 and L3 are 1-7, 2-8 and 3-9.

James

It's a wye, but why bother with anything further testing?
2 of the 6 windings are clearly messed up as reported. Those 3 point connected windings have 2x the value as the apparent remaining single good winding as would be expected.

If each separate winding and the 3 connected internally (sometimes broken out as 10, 11, 12) all showed good values, then a megger would be a good test for possible further info.

 

[kngelv]

I agree with your earlier methodology suggestion but I suggested the megger because sometimes you get weird ohm readings on windings depending on what meter you’re using. Plenty of people use **** meters and get screwed up readings. Using a decent megger to put a load on it is the best way to test a 3-phase motor.

James

 

[tool_scrounge]

For future reference, for older motors you could consider adding a filter between the VFD and the motor.

https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/line_reactors_-a-_output_filters/lr2-21p0

 

[Innovate1]

For future reference, for older motors you could consider adding a filter between the VFD and the motor.

https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/line_reactors_-a-_output_filters/lr2-21p0

That's a good suggestion and they have 460V units (460, 480 whatever it takes... Seriously I wouldn't get too hung up on that small difference). Have used Automation Direct before but not for line inductors. Was not aware they had those and prices are reasonable.

 

[nadogail]

Every piece of electrical equipment was built with smoke secretly installed at the factory, once the smoke leaks out your equipment won't work like new; if it will work at all.

 

[mm08822]

Every piece of electrical equipment was built with smoke secretly installed at the factory, once the smoke leaks out your equipment won't work like new; if it will work at all.

Most stopped putting the special bbq sauce inside however.

 

[dave*99]

These folks are experts on smoke.

 

[mm08822]

These folks are experts on smoke.

Found next to the blinker fluid?

 

[wyliesdiesels]

Found next to the blinker fluid?

and muffler bearings...