IR measurement for OHL

[RRaghunath]

It is normal practice for electrical engineers to check IR before energising any equipment. I understand that the OHL gives a very low IR due to the numerous insulators and also due to the line to ground capacitance. Typically a 50km long 132kV OH transmission line could give as low an IR as under 1 megohm.

Is it true. Then what is the appropriate way to confirm the insulation integrity before charging the line with rated voltage. Can you please suggest.

Thanks in anticipation.

Raghunath

 

[busbar]

Generally it’s more common to figure that such a measurement would be useful immediately before energizing to show simply that there are no grotesque problems. For equal voltage and current, shielded cables will have higher leakage and comparatively lower insulation resistance.

 

[kittiga]

faulty,
I had the oppurtunity to carryout IR test on a couple of lines before energisation. One was 33kV,46km long and the other a 220kV line 55km long. In both the cases i was not sure of the acceptance critera - so just used the thumb rule of kV + 1 MOhms as minimum.
In both the cases the values were not as low as you state - although i found a drastic change in values as the sun rose ( the testing was on cold mornings in sandy deserts). My suggestion for testing and commissionig would be - clean all insulators if possible and dont test when you suspect a lot of dew on the insulators.