# Proper Testing of a 480v 3 phase induction motor



## digidoggie18 (Nov 5, 2016)

Hey guys, 

I am brand new here however, I am not brand new to doing electrical work. What I was wondering is what is the full on proper way to test this type of motor. I am wondering because I will be setting up test procedures for doing so where I currently work at. 

As of right now, All we currently do is check each wire to ground and megger the motors. Currently I know our meggering the motors is incorrect as they test the motors at only 500v From all the reading I have done I know we should be meggering them at 1000v. 


One issue I had recently though was a motor with brand new bearings was built and it sounded like it was wired incorrectly. So I deemed the motor bad because our wiring was correct. When I dug a little bit further into the problem I found that two wires from the motor had resistances of 275k and 350k at which point we deemed the motor bad.

How exactly can I properly test these motors to 100% ensure that they are bad, does anyone have any input?


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## Southeast Power (Jan 18, 2009)

How did you decide that 1000 volts was best?


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## Flyingsod (Jul 11, 2013)

digidoggie18 said:


> Hey guys,
> 
> I am brand new here however, I am not brand new to doing electrical work. What I was wondering is what is the full on proper way to test this type of motor. I am wondering because I will be setting up test procedures for doing so where I currently work at.
> 
> ...


Firstly a 500 volt megger is most likely fine. EASA says for 2400 volts or less motors use a 500. Over that a 1kv megger Is recommended. 

The next test is a polarization index test

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## brian john (Mar 11, 2007)

NETA standards state 1000 VDC for 600 VAC equipment but 500 VDC should have been fine.


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## Flyingsod (Jul 11, 2013)

(Accidentally hit send before I was done with the last post)

The P-I test is basically a megger that can be hooked up for ten minutes and you record the readings at the start and finish times then do the calculation.

Another test used is a high potential test. Commonly called hi-potting. There's a lot of problems with this one for the un initiated. You can easily damage the motor windings you are trying to test, the test equipment, or yourself. I'd leave this one to the motor shop.

In the field you really don't need any more than an ohmeter and megohmeter. Make sure the windings are not grounded with the megger. Make sure each individual winding has close to the same resistance. Anything else requires specialized equipment and it's most efficient to leave it to the motor shop. GL


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## John Valdes (May 17, 2007)

Your best test if possible after doing all these things posted above is a load test. A surge tester can also be a very good way to determine motor health.


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## Big John (May 23, 2010)

For diagnostics at the very least you should be doing a 1 minute meg to get your DAR. For 600V class equipment you test at 1kV. But if I were doing OEM 120V motors, I'd probably knock that down to 500V.

If you have access to a high current DC source or variable AC source you can do winding resistance/impedance and compare between phases.

You can check shaft run out with a dial indicator, but it's often best to actually get vibration especially once coupled to the load.

I'm also a big fan of surge testing, but that equipment can be tough to come by.

I'm not a huge fan of hipotting unless doing commissioning or trying to flush out an incipient problem with the understanding that the test may render the motor unsuitable to return to service.


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## digidoggie18 (Nov 5, 2016)

Suncoast Power said:


> How did you decide that 1000 volts was best?



I looked everything up and found a chart that states the nominal rating of the equipment and the minimum test voltage along with the minimum insulation resistance. However, the chart goes from 250 up to 600. Our motors will run at 480v but with that being said everything else is rated at 600v so I went with the next highest setting in that table which is 1000v for the megger. 

The reason I am asking is because we are megging the motors and ohming the windings as well as the 3 thermistors in the motor and still getting bad motors.

How would one do a surge test? I haven't heard of this before.

As for DC power supplies, we have a whole boatload of those for testing that range from high voltage to low voltage. We mainly use them to test low voltages though i.e. opening solenoids, energizing control circuits


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## digidoggie18 (Nov 5, 2016)

Big John said:


> For diagnostics at the very least you should be doing a 1 minute meg to get your DAR. For 600V class equipment you test at 1kV. But if I were doing OEM 120V motors, I'd probably knock that down to 500V.
> 
> If you have access to a high current DC source or variable AC source you can do winding resistance/impedance and compare between phases.
> 
> ...


None of these motors are 120vac motors. They are all industrial 480v motors
Normally we have nothing wrong with the 120vac motors


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## digidoggie18 (Nov 5, 2016)

Basically what this stems from is this week we meggered a motor and found that it was good , when we went to use the actual motor it was noisy like it had been wired incorrectly. When we checked the wiring it was correct so we pulled it off the pump and put a different motor on and the pump ran like a dream. when we hooked up the noisy motor without load she was quiet however, we also found a high resistance condition along 2 windings. causing a phase imbalance essentially. I am trying to figure out testing to ensure that we will most likely never test another most and deem it good when it is bad


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## Flyingsod (Jul 11, 2013)

By your description you did not ohm the windings before service. Surely you would have noticed two of the windings being in the kilohm range and not but the motor in service. 
Our motor shop has experienced motors that Meg and ohm good but still have an issue but it's a hell of rareness. In 17 years of being a service tech I have never personally come across one. It happens yes, but I feel the extra effort need to ferret then out is not worth the effort for anything but a motor shop.
If your Institution is that serious about maintenance though I suggest looking into an EASA membership. They have the educational resources to teach you all that kind of stuff. GL

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## Big John (May 23, 2010)

Remember that you're looking at different parameters:
You can have a motor with all around fantastic insulation resistance that still won't run because of a winding or bearing problem.

That's why I suggest doing high current impedance tests: You're checking both winding continuity and configuration. If you have an iron or rotor problem it may show up in the impedance that you would never see in the pure resistance test.


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## inetdog (Apr 13, 2016)

Big John said:


> Remember that you're looking at different parameters:
> You can have a motor with all around fantastic insulation resistance that still won't run because of a winding or bearing problem.
> 
> That's why I suggest doing high current impedance tests: You're checking both winding continuity and configuration. If you have an iron or rotor problem it may show up in the impedance that you would never see in the pure resistance test.


And a shorted turn on a winding will very likely not show up in a DC test, but will be very visible in a running current test.


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## digidoggie18 (Nov 5, 2016)

Big John said:


> Remember that you're looking at different parameters:
> You can have a motor with all around fantastic insulation resistance that still won't run because of a winding or bearing problem.
> 
> That's why I suggest doing high current impedance tests: You're checking both winding continuity and configuration. If you have an iron or rotor problem it may show up in the impedance that you would never see in the pure resistance test.


We are actually trying to do everything for the motors. Currently we supply both end plates that we have machined in house for certain motors that have spun the bearings. Competitors have been sleeving the bearing housings and then machining those to fit the bearing, we are also putting in new bearings as well as a thrust washer. Recently however we have had problems with our S&K bearing manufacturer that is sending the bearings without grease which we do not notice until run time when we get noise due to it being a sealed bearing. Thank you for the help!


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## digidoggie18 (Nov 5, 2016)

Flyingsod said:


> By your description you did not ohm the windings before service. Surely you would have noticed two of the windings being in the kilohm range and not but the motor in service.
> Our motor shop has experienced motors that Meg and ohm good but still have an issue but it's a hell of rareness. In 17 years of being a service tech I have never personally come across one. It happens yes, but I feel the extra effort need to ferret then out is not worth the effort for anything but a motor shop.
> If your Institution is that serious about maintenance though I suggest looking into an EASA membership. They have the educational resources to teach you all that kind of stuff. GL
> 
> Sent from my C6725 using Tapatalk


Currently we get them here and there. Normally it's due to amanufacturer problem with our bearings that we have been having recently however the rest we get the windings do actually ohm good and the megger tests come back good. We are serious about maintenance since I have gotten there. Since I got there I have showed them how to properly repair some circuit boards as well as other pieces that they used to normally send out. For example the boards I am repairing we can do in house for like 2$ when they send them out it ends up being 500$+. Currently we are on track of revamping all aspects of what we are doing right now with these pumping systems. I just recently set up a heating and flushing tank for some of our coils for cooling the pumps as they were getting clogged with scale. I appreciate the help and I will definitely look into an EASA membership!


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## KennyW (Aug 31, 2013)

Surge tester /Baker tester is the most definitive but not cheap. It's not the sort of gear and end user usually deals with. Sounds like you are megging the rtds. I would definitely not do that.... 

What sort of hp are we talking about here?


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## digidoggie18 (Nov 5, 2016)

KennyW said:


> Surge tester /Baker tester is the most definitive but not cheap. It's not the sort of gear and end user usually deals with. Sounds like you are megging the rtds. I would definitely not do that....
> 
> What sort of hp are we talking about here?



We Definitely do not megger the PTC Thermistors in the motor. It is only each winding to the case. We only ohm these thermistors although the ohming of them is inconclusive at best. Normally they ohm them at room temp and if they read they deem them good, I suggested a better route of us ohming them during the actual testing and running of the motor as at operating temp they are supposed to read between 100 and 500 ohms and at overheating they should read 3000 ohms.

Our motors range in hp between the only 3 pumps in which we actually test the motors. The other ones we have are hermetically sealed motors that we just toss or send to taiwan for repair.

They are as follows:

4hp
7hp
and 9hp

What we do is megger the windings on these like stated above to the case.

After that we ohm the windings however, I would have to look it up exactly but I do believe they were at one point doing it incorrectly. This is something I would have to look at tomorrow to verify personally as I normally don't assosciate with that section of the shop. The reason it came up was because I was asked to help this new guy test the motor by itself. We ran it up and it was quiet as heck but then I went through and ohmed the windings what I ended up doing was ohming U1-U2, etc... Winding beginning to winding end and found the high resistance condition. How much are we talking in doing a baker test/surge test?


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