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crpal
Member

Join Date: Jul 2011
Posts: 7

PI Value of Synchronous Generator

08/03/2011 12:05 PM

During the commissioning of a Synchronous Generator of a thermal power plant we are obtaining PI(Polarization Index) in the range of 1.1-1.37 with the IR value ranging from 180 Mohm to 210 Mohm. But the customer demands a PI value of >2.5. Can anybody tell me what is the the standards(Indian and International) for this PI value?
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Pathfinder Tags: Generator PI value
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msamad
Guru

Join Date: Feb 2009
Location: Houston, USA
Posts: 946
Good Answers: 244
#1

Re: PI Value of Synchronous Generator

08/03/2011 9:51 PM

Per IEC 60085-01 and IEEE Std 43-2000, the required PI values are

Insulation class

Minimum P.I.

Class A 1.5
Class B, F and H 2.0

Also see these comments:

http://cr4.globalspec.com/comment/476214

http://cr4.globalspec.com/comment/386276

- MS

__________________
 "All my technical advices in this forum must be consulted with and approved by a local registered professional engineer before implementation" - Mohammed Samad (Linkedin Profile: http://www.linkedin.com/in/msamad)
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pcchatur
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Join Date: Mar 2010
Location: BHOPAL, INDIA
Posts: 201
Good Answers: 20
#2

Re: PI Value of Synchronous Generator

08/04/2011 12:15 PM

Please give more details of the generator. Namely, rated voltage, winding capacitance, class of insulation. I presume that you are measuring the PI of stator winding. In case of rotor winding (which is a low voltage winding), PI has no relevance. If the capacitance is low, it would get charged quickly and therefore, PI (ratio of IR after 10 minutes to IR after one minute) will be less than two. Have you ever achieved the PI value of the order of 2? If yes then you need to dry out the winding insulation.
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