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3 comments
Participant

Join Date: Nov 2010
Posts: 2

Standard Temprature Correction Factor of Winding Insulation Resistance

11/30/2010 1:06 PM

Please someone tell me the Standard Temprature correction factor of winding insulation resistance of 3X150MVA,500/220KV auto transformer,in the light of international standard.As well as the minimum acceptance limits and calculations. Thanks and best regards.

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Power-User

Join Date: Jun 2010
Posts: 350
Good Answers: 10
#1

Re: Standard Temprature Correction Factor of Winding Insulation Resistance

11/30/2010 11:09 PM

Formula for temperature correction:

R40 = K x Rt

Where R40 is the insulation resistance Mega Ohm corrected to 40 deg C.

Rt is the measured resistance at actual site temperature

K = 10 (0.0301 t - 1.2041)

This means roughly a resistance re-doubling at every 10 deg C of decreased temperature and vice versa.

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Participant

Join Date: Nov 2010
Posts: 2
#3
In reply to #1

Re: Standard Temprature Correction Factor of Winding Insulation Resistance

12/06/2010 1:34 PM

hi ,i am graetful to you that you guide me in this matter,kindly guide me about the formula for calculating the minimum insulation resistance of T/F wdgs at 15sec,60sec or 600sec.once again i am thankful to you.best regards.Engr.Asim

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Power-User

Join Date: Jun 2010
Posts: 350
Good Answers: 10
#2

Re: Standard Temprature Correction Factor of Winding Insulation Resistance

11/30/2010 11:27 PM

For transformers rated 110 Kv and above 60 seconds insulation resistance in mega - ohm is 240 for a winding temperature of 40 deg C.

Please note that yo have to carry out polarization index (PI) test which is a ratio between IR values for time intervals 1:10

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