PT Testing-Negative Tip Up

[merjer2005]

We have been power factor testing oil filled potential transformers of different primary voltage levels and we have been getting some tests that are exhibiting negative tip up. It looks like this is due to the power factor being slightly worse at 2kv than at 10kv test voltage(at least thats how I understand it). Does anyone have any information on this or know why this happens?

[backpack96]

We have been power factor testing oil filled potential transformers of different primary voltage levels and we have been getting some tests that are exhibiting negative tip up. It looks like this is due to the power factor being slightly worse at 2kv than at 10kv test voltage(at least thats how I understand it). Does anyone have any information on this or know why this happens?

Often times a negative tip up is due to the test results being carried out to the third place. The currents and capacitances at 2 kV and 10 kV should basicially be equal. The 10 kV watts may be ".128" while the 2 kV may be ".131" which would result in a negative tip up. Only .003 watts different so no concern. I have seen results in which both tests were performed at 2 kV and still received a negative tip-up with the watts being a little different.

If this is a line to ground PT then normally 10 kV is not applied, except when only the H1 bushing is energized when the H2/H0 bushing is energized as that bushing is normally a smaller bushing. All other tests, including exciting current, at 2 kV or 5 kV.