Isolation Transformer test

[arun17]

Hi friends!
I am a mechanical engineer, but I need to know the isolation between primary and secondary and secondary to ground for a 150 KV type isolation transformer. Can anybody suggest where I can find the procerure for this. Is there any ISO guideline for this?
Thanks
Arun


"Knowledge is power"

 

[moreause]

for me all always do maintenance test with a 1000 v megger

1-on hign voltage (with lo side grounded)
2-on low side (with high side grounded)
3-on low and high side(at the same time)be carreful to have an clean and a bit of isolated jumper

normally number 3 gives you the lowest of 1 and 2

if you have doubt on the insulation you can rise the test kv to work the insulation.

since this seem to be a big transformer, maybe a pf (doble testing) would be to consider

doble gives you much more info on the state of the insulation

 

[arun17]

Hi!
Thanks for your advice. I have already done maintainance test with 1000 v megger. I heard about lightning impulse test. Can that be used for Isolation transformer. I would like to know if ISO or any othe code gives guideline for it?
Arun


"Knowledge is power"

 

[Zogzog]

Wait a minute, am I reading this right? You are testing a 150kV transformer with a 1000V megger?

 

[arun17]

Soryy friend ,
I am testing insulation resistance with a 1000 V megger. This resistance tells us something about the health of insulation. If there is a degradation of insulation this resistance goes down and more leakage occurs through the insulation which ultimately results in loss of voltage.
Now the problem is that, although you may get a good insulation resistance at this 1000 v but when you apply actual voltage , still leakage may be more than the estimated one due to dynamic behaviour of solid and liquid insulators.
Any suggestions?
Arun


"Knowledge is power"

 

[lz5pl]

arun17, I don't know how many volts are required by your NEC for such testing, but in my practice in Eastern Europe, Middle East and Africa we always use 5 kV Megger for equipment over 11 kV. I have tested insulation of same oil filled measuring transformer by 1000V and 5000V range of the same (calibrated!) megaohmmeter and the results were different. Difference was not drastic, but sufficient to compromise the analise of routine tests results.
And of course you are perfectly right, that energizing with real voltage is something very different from insulation resistance test, never mind 1000 or 5000 V. (-:

 

[unclebob]

Wait a minute! Your transformer must be 115 KVA if it is really an isolation transformer. The primary and secondary voltages must be the same. So the megger testing at 1 KV is
adequate. As for the lightning impulse test, you must
be refering to the BIL (Basic Impulse Lightning). This is not a routine test as it may be destructive. It it used for newly designed equipment.

 

[pwrengrds]

What is the primary and secondary voltages?
What is the kVA? Is it 3phase or single phase?
That will determine the types of tests. If it is less than 600 volts then the megger tests at 1000 vdc would be generally acceptable for operation. If its really 150kV a doble test, turns ratio, among other tests would be expected.

 

[arun17]

Dear friends,
It is a 100 KV, single phase isolation transformer with 20 amp. rating. This is not a step up or step down transformer. It is a 1:1 transformer. The isolation between primary to seconday is 100 kv and secondary to ground also 100 kv.
Thanks
Arun

"Knowledge is power"

 

[JBinCA]

How big is the transformer physically? Is it the size of a TV? A Car? If it's truly a 100kV 20 amp transformer, that works out to 3460 kVA, which would be no small transofrmer. The tank alone would probably be 10 feet long by 10 feet wide by 15 feet tall. The H1 and X1 bushings would be five foot tall peices of porcelain sticking out of the top of the transformer taking the total height to 20 feet.

If your transformer is more along the size of a TV, then it's a 150 kVA unit (or 100? - you changed your story), not 150 kV.

Best Regards,