LV Motor Megger Test

If you were using a Hi-Pot instead of a megger, then you probably damaged the winding insulation; a Hi-Pot is a destructive test (and more if AC is applied).

A megger test won't damage the insualtions since it has very little current capacity and it applies a DC voltage.

As per the specifications of a Hi-Pot test I've read in some manuals from Quadtech that one comon practice is to apply twice the rated voltage of the device under test, plus 1KV, doesn't refer to any standard or norm, it is just something widely accepted.

Regards

Handy sheet, thanks.

What would happen - Bang

Go & get a 500V Megger & use that. You do not have to test it for 60sec.

I found the readings on small motors rarely changes after about 15 secs. Usually you will find any problem before that. If it is still moving (generally downward) then the motor is wet - so dry it out.

Dear Alirahnama,

first of all why you want to take such test, any specific reason?

All the fellow members has responded to your question and You must be satisfied with the answer, but please give your feedback on this!!!

Subhash

Dear Subhash,

i have read somewhere on megger tester manual that in DC insulation test there is just some mili amps current beside the stable voltage without any spike so in my point of view this situation could not creating harmful condition or damage the winding insulation.

i think there is difference issues among hi pot test by high voltage Ac current and megger test which is used as diagnostic and is intended to be nondestructive test which could be repeated on the same device.

so i keen on it by use higher voltage ( than regular 500VDC) and time due to getting assure on healthy insulation of winding in absence of some other test.

thank you so much but i'm not for you.

Motor insulation may get damaged if you use 2500 V megger. For a 400V motor 500V megger is recommended. However you can go maximum upto 1000V megger.

Interesting. US Gov has a different idea, this is for a post repair test:

"For rewound motors, a DC high potential test shall be conducted at 1700 VDC for motors to be powered by less than 250VAC service voltage. Motors to be powered between 250VAC and 600VAC service voltage shall be tested at 1700VDC plus 3.4 times the machine's voltage rating, e.g. 3264VDC for a 460VAC machine. Readings corrected to 40°C, which are less than 20 megohms, shall be discussed with purchaser."

From http://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/repair_specs_motors.pdf

So the test should be performed at 3060VDC.

We never "Hi-Pot, PI, DI, or Surge" test with our Baker or Megger over 2000 Volts.

It will show up a "turn to turn, Phase to phase or Phase to ground" fault at that voltage, any higher may damage a motor that has been in service. What you are saying is correct for a Motor Mfg. or Rewind shop standards, the difference is if they "pop" a winding they eat the motor not us end users...

500V is enough for you.

Refer IEEE 43-2000 for ratating machines for maintenance prpose and for manufacturers.

If you keep it simple then you'll not go wrong.

try 1000v for 3 mins.

I use it all the time on motors rated at 2000v plus, and that includes the 2000M of cable attached to the motor.

oh my !!!! you will destrowing the motor waaaaaahhhhhhhhh 2x the motro voltage only is good <