IEEE 43-2000 Theory applied to XFMRS 1

[SCERS]

Can anybody tell me if they relate practices from IEEE 43-2000 "Recommended Practice for Testing Insulation Resistance of Rotating Machinery" to transformers. My specific question is if when performing a P.I. on a transformer, if your 60 second reading is greater than 5000 megohms, do you continue until 10 minutes, or abandon testing?

 

[prc]

Standard 43-2000 is not applicable to Transformers.Incidently,IEEE Std 43 was revised in 2013. Most of todays transformers with high resistivity oil will give a IR more than 5 Mohms. The standatrd applicable for trnasformers is C57.152-2013( earlier 62-1995) Diagnostic field Testing of Transformers.
Clause 7.2.13.4 of standard:

Polarization Index = 10 min insulation resistance (megohm) reading/
1 min insulation resistance (megohm) reading
The following are guidelines for evaluating transformer insulation using polarization index values:
Less than 1.0 = Dangerous
1.0 to 1.1 = Poor
1.1 to 1.25 = Questionable
1.25 to 2.0 = Fair
Above 2.0 = Good
The polarization index method should not be used to assess insulation condition in new power
transformers.
The polarization index for insulation liquid is always close to 1. Therefore, the polarization index for transformers with low conductivity liquids (e.g., new mineral oil) may be low in spite of good insulation condition.

 

[SCERS]

Thanks for your response. I probably should have specified on a dry type VPI XFMR.

 

[Millbo]

SCERS,
The Megger publication, A stitch in Time" states the following: "...Acceptable insulation resistance values for dry and compound-filled transformers should be comparable to those for Class A rotating machinery, although no standard minimum values are available...."

IEEE Standard 43, section 12.2, table 2; lists the minimum PI for Class A rated machinery at 1.5