Power Factor Insulation Testing - Natural Esters

Electrical Testing Talk
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When conducting insulation PF tests, for liquid filled natural ester/ester transformers, why does NETA ATS ask for a max of 1% PF but NETA MTS indicates a max of < 3% PF? (refer to table 100.3 in both standards, assume no manufacturer test results/guidelines are available).

Many natural ester transformers can’t meet the NETA ATS standard, or just barely pass.

If the PF result comes back greater than 1%, but less than 3% would you still accept it during the ATS testing portion or fail it? What do you do if it fails as the equipment owner?

Curious to know anyone’s experience regarding this.

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The old general rule that may or may not apply to NE is if it’s less than 3mva, make a comment that it exceeds neta specification and requires trending. if it’s bigger than 3000, you should call the mfg and get them to approve your results which they always do. It’s not very reasonable to call a transformer defective on power factor percent alone without a trend.
This isn’t any NETA or ANSI standard, it’s an old company operating guideline to keep guys from troubleshooting transformers for hours when they’re actually fine and nobody cares about smaller padmounts anyway.

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