Motor IR testing

[tmcgett]

I have been searching the web for some "basic" guide lines to follow on doing a insulation resistance test on motors.

I seem to be getting inconsistent procedures on test voltage range and in particularly "lead placement".
For insistence:
I have read test voltage range <1000v = 500vdc range and also read test voltage range is set at 2x motor voltage.
Lead placement is all over the place from; to ground, across winding, connect the motor leads, I'm confused!

I am looking for some old school, rule of thumb advice on testing a WRIM, 3 phase, Wye - 480v, 76kw (in the field)

Regards

 

[electricpete]

IEEE43-2000 is the standard which should resolve the issue of "all-over-the-map" recommendations. You have to pay to purchase that Standard.

Some free info on-line here:

http://www.usbr.gov/power/data/fist_pub.html

(see item 3-1: "Testing Solid Insulation of Electrical Equipment, December 1991")


=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

Per IEEE43-2000 - your test voltage should be 500vdc.

2x voltage is not correct for an insulations test... it is is roughly related to hi-pot test - factor ac-hi-pot done at 2*E+1. Maintenance level dc test in the same ballpark.

Your acceptance criteria is a 1-minute temperature-corrected insulation resistance value of 100 megaohms. (Older windings were kv+1).

Test voltage should be applied to the machine winding (checking insulations resistance to ground). Which of three phases doesn't matter although I believe the standard might suggest to connect all three phase terminals together.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[jtkirb]

Let's say you have a 6 leaded motor- isolate each winding (2 leads) and ground everything else. Test each winding to ground. That would be 3 seperate tests- 1 for each winding.

Make sure you hook the motor back up correctly.

JTK

 

[tmcgett]

jtkirb

What about the rotor ( 3 wire )
Would you need to ground them while megging the stator

THANKS : jtkirb and electricpete