Insuation Resistance Problem on Generator Stator

[shkim2000]

I measured insulation resistance by Megger and it reads 5 MOhm. P.I is approximately 1.0. I believe that this value indicates poor insulation. I assume that humidities are ingressed into generator due to long term storage. I will heat it up.
If it is not humidity problem, I'd likw to know any other possible reasons I may assume, such as PT installation or any others ?

 

[alehman]

More information please - size of genreator and voltage rating would help. What was the megger voltage. 5M seems low.

 

[shkim2000]

Generator is rated at 2250kVA/6.6kV. It has been measured by 2500VDC.

 

[edison123]

Isolate PT and check.

* If you have never succeeded in anything in first attempt, skydiving isn't for you. *

 

[motorspert]

5M is low and a PI of 1 suggests either cables, lightning arrestors, surge capacitors or PTs are in circuit OR a problem with the insulation. A low PI is a classic indication of damp - so heating is a good idea, if you have some dehumidifiers handy then blasting in some dy warm air will help.

If possible, seperate the neutrals and check each phase individually.

You don't mention the field/exciation circuits are they ok?

 

[alehman]

Are you sure that's not 5Gohm?

 

[alehman]

thread238-42630

 

[Chad12]

I agree that all connections must be isolated to perform this test, yes humidity is a big factor, and there is also a temperature correction factor that must be applied.

Chad Snyder
Director of Operations
American Power Technology

http://www.ampowertech.com