Transformer testing
Transformer testing
(OP)
Hi Guys
Can somebody please advise me as to what voltage can a SGB 33/6.6 kv transformer be tested at during a pressure test?
I would normally test any 33kv transformer at abt 15kv dc between phase and earth as it will be working voltage, but phase to phase i'm not sure abt. I'm using a T&R pressure test kit.
thanks
Can somebody please advise me as to what voltage can a SGB 33/6.6 kv transformer be tested at during a pressure test?
I would normally test any 33kv transformer at abt 15kv dc between phase and earth as it will be working voltage, but phase to phase i'm not sure abt. I'm using a T&R pressure test kit.
thanks






RE: Transformer testing
For acceptance or routine maintenance test,in my opinion the best reference is NETA Acceptance Testing spec or NETA Maint Testing Specification.
RE: Transformer testing
RE: Transformer testing
RE: Transformer testing
Can't help on the test voltage but will have a look when I get in to work and post any information I find.
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If we learn from our mistakes I'm getting a great education!
RE: Transformer testing
Usually the overpotential test is done High to Low with low side grounded. Low to high with high side grounded, and high to low. A megger test is done followed by a PF test. The 33kV side should be meggered at 5000VDC or more and the 6.6kV side at 2500VDC or more. The minimum spec depends on dry or oil type as do your specs for the PF test.
I do not know of any standard that recommends a DC hipot test on transformers.
RE: Transformer testing
the purpose of a voltage withstand test is to prove that the insulation is in good order and it is safe to connect up the working voltage. I appreciate the insulation resistance tests with the megger and the low voltage of 5kv but it is sometimes not to great to prove a potential fault.
Example, i tested a transformer at 5kv with a megger and it proved ok, when I performed a 'pressure test' the insulation broke down. That was a 11kv transformer that I injected 12.5kv, a new cable was terminated to it and the recommended test was 2,5 times working voltage per phase.
So in that respect, how do we prove that the 33kv transformer insulation is safe enough to energise. Does your megger on 5kv give you the satisfaction.
Thanks again.
RE: Transformer testing
We then perform an induced high voltage test, which overstresses the insulation between the turns of the windings.
The 2 tests perform very different functions. These are in addition to the insulation resistance tests.
Don't forget about all the low voltage tests that need to be performed, which act as good benchmarks for the future, as well as giving more confidence for energising it - resistance, ratio, FRA etc
Without these tests, you can really cross your fingers for energisation.
ausphil
RE: Transformer testing
RE: Transformer testing
Why would you limit NETA to North America? It is an international standards and has member companies worldwide. That said, NETA specs always say to follow manufactures recomendations and provide guideance in the absence of them.
Shocker,
As I said before, the megger test is done before the higher voltage test, the PF test, that is a much better test than a hipot (Pressure, dielectric, whatever you want to call it) test, it gives a truer indication of the insulation condition.
RE: Transformer testing
This is the first time that I have dealt with the power side of a 33Kv transformer, I normally concentrate on the protection part.
RE: Transformer testing
RE: Transformer testing
we apply 70KV (for 33KV winding) in power frequency withstand test for one minute and check transformer
and we apply abt. 25 KV after that for partial dischage test in order to chech the 33kv winding insulation .
thanks