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scooby1981
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Join Date: Sep 2009
Posts: 6

PI for Generator Rotor

11/05/2009 4:21 AM

I have tested rotor of 30 MW gas turbine 2-pole generator and the results are as under:

Insulation resistance = 33,882 Mohms

Dielectric absorption ration (IR60 second/IR30 second) = 1.10

PI = 1.46

Dielectric discharge ratio = 0.66

I would like to know the minimum acceptable DAR and PI values for healthiness of the generator rotor.
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PWSlack
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Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
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#1

Re: PI for generator rotor

11/05/2009 4:43 AM

What does the original equipment manufacturer's operation and maintenance manual have to say on the topic?

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scooby1981
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Join Date: Sep 2009
Posts: 6
#2
In reply to #1

Re: PI for generator rotor

11/05/2009 5:00 AM

As per GE - A field index (PI) of 1.25 would suggest a clean, dry field winding.
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msamad
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Location: Houston, USA
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#3
In reply to #2

Re: PI for generator rotor

11/05/2009 4:27 PM

(1) Dielectric Absorption Ratio (DAR) = (IR 60 seconds / IR 30 seconds)

Recommended DAR values

DAR Values

Result

Less than 1.1Bad
Between 1.1 to 1.5Good
More than 1.5Excellent

(2) Polarization Index (P.I) = (IR 1 minute / 10 minutes)

Recommended minimum values of PI for all machine components insulation classes per IEC 60085-01:1984 or IEEE Std 43-2000

Thermal class rating

Minimum PI

Class A1.5
Class B2.0
Class F2.0

See the following links:

http://www.termogram.com/articulos/Understanding_Insulation_System_Testing-Don_Shaw.doc

http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=AEMC_insulation.htm

- MS

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