HV Switchgear Insulation Resistance

is that 1 minute value or ten minutes value.

reg

We did the IR test with Megger.

The one minute or ten minutes test is done with separate AC supply and we didn't do it.

You should ask the manufacturer for the minimum value allowable and one think is that I have observed that with the increase in voltage at which you are taking IR the value of IR decreases a little.Also you should measure Polarization index and then compare the values..

According to InterNational Electrical Testing Association reference book your voltage ratings require 100 MegOhms. This figure in my opinion is too conservative.

But based on my experience, this value is too high. We have energized and continued operating 69 kV power trnsformers and SF6 power ckt bkrs whose one minute insulation test readings fall between 10 - 50 MegOhms at ambient tempratures between 30 - 38 deg Celsius and humidity between 60 - 80%. And yes, we do clean the bushings before testing. We've been doing this for many years now and not one of our equipment failed.

We rely more on the Polarization Index and Tan Delta - sweep frequency/sweep voltage, although these take a lot of time to completely perform. Based on our experience, you can never go wrong on this two methods of insulation tests.

We've also tried the formula Ins. Res. = CE/(kVA)^0.5 and the 1 MegOhm per kV plus 1, but they all don't work for us.

Honestly, for me, interpreting IR test results is a lot more challenging compared to the tan delta.

We did the tan delta test for power transformer only.

We never apply it to CB, CT and CVT. Can you introduce the standard which required tan delta test for CB, CT and CVT; I would like to suggest it to PLN. ( Indonesia Electric Power Co. )

For your information our ambient temperature range is 29 - 32 degreeC and the humidity between 89 - 95%.

In my opinion its rather risky, to energise the switchgear who'r IR is only 10 MOhm, but this a good information,as long as the switchgear can operates safe and sound.

Sorry for my typographical error in #3. It's "10 - 50 MegOhms GigaOhms."

Tan delta test can be performed on any type of equipment insulation. If you have the testing guide of Doble Engineering, it details and explains a lot. The tan delta test manual of Megger Intl is also a very good guide.

Thank you,

I'll contact my friend who is the agent of Doble at Indonesia regarding this matter.

regards,

Stanyadji