RE: Busbar Insulation Resistance Testing

[jaimse00]

This is a blast from the past....
I was browsing through the archives at thread238-67387 and was wondering about the answer to the original question.
Where I work We have always used 20Gigs @ 5kV for testing 11 & 33kV CB bushings (also used by default for the insulated buswork). I haven't really seen the justification for this - it just always has been the standard (albeit with a bit of interpretation for test conditions).
What do people generally accept as an ok IR result when maintaining 11kV or 33kV switchgear? Does the answer change much when considering indoor vs outdoor breakers or even outdoor @ 66kV?

Just curious what general practice is for others.

 

[Zogzog]

I don't know about anyone else but I always follow ANSI/NETA testing specs.They provide minimum test voltages and minimum acceptable values.

 

[jaimse00]

Hi Zogzog,

Thanks for responding.
These are standards for maintenance testing switchgear and busbars? Not to sound completely green, but what do these specs recommend?

 

[Zogzog]

Depends on what class of gear, acceptance or maintenence testing, and AC or DC test. You can purchase the standards here.

https://netforum.avectra.com/eWeb/Shopping/Shopping.aspx?Cart=0&Site=NETA

 

[VLFit]

there are so many reasons why DC testing is not the best approach. It can be used, but ther are many items in a substation that really should be AC hipoted. The surest way to determine if the bus bar, insulators, vacuum bottles, etc are solid is to perform an AC Withstand test. Follow the ANSI, NETA,....etc test numbers. If the load holds the AC voltage of 2 - 3 times normal depending on the item and the standard, it's good. There is nothing ambiguous about it as there is in DC testing where many variables can effect the IR or leakage current readings.

 

[dpmac]

Vlfit,

The OP was simply requesting info on recommend test values when performing 5kv Insulation Resistance tests on equipment rated 11kV and 33kV. In most cases a DC IR test is performed prior to other tests be it AC, DC, VLF, etc. In many cases it may be only test required. Are you suggesting the DC Insulation Resistance test not be performed prior to other tests or not at all?

 

[VLFit]

Hey dpmac. always looking for the debate. no problem.

You are right in in your reply that he was merely asking for help with the test numbers, but to only answer that would ignore the 800lb gorilla in the room. One could have suggested test numbers from some source but that would still not be the end of the story, for as you know, with the many variables involved in DC testing, especially air insulated apparatus subject to varying atmospheric conditions that could throw the measured values from one end of the scale to the other. The test is worthwhile a a rough check of things, like if a ground was left on the sytem, it is no measure of the integrity of the eqipment with any ind of certainty and repaeatability. If it's all you've got, then thats's that. But taking it one step further and suggesting that instead fo that test, or in addition to it, if you have an AC hipot avaialable, that's the better way to go. Of course you know all of this and are just playing the debate game for the benefit of readers, which is great, I am trying to make sure that alternate methods to DC are investigated and that people stop to think about the physics behind the tests they do and what is actually happening and what it tells them. As with any testing, one must first ask what are the desired test results meant to reveal and once known, what can/will they do with the data.It's amazing how many people perform tests without any regard to the worth of the data collected and the actions available to take using that data.

Say hi to the gang.

 

[Ceast]

Precisely why we commisson equipment, gathering baseline data with temp correction and himidity recordings. On well maintained equipment you typically don't see dramatic changes between EPM's. Always refer to the NETA standards for device testing & insulation resistance limits.