PCB transformers standards
PCB transformers standards
(OP)
Hello everyone,
We just tested 2 PCB transformers: ratio, winding resistance, PCB dielectric breakdown and insulation test (megger @ 1kV).
All the tests gave good results on both transformers, but the insulation tests we're pretty low on -both- transformers primary side (about 8 to 9 MegOhm for a 25kV primary side).
The test instrument was working well because we tested surge arresters minutes later and they gave high results. The tests were indoor and the humidity level was not high.
Is there any special conditions or internal configuration in PCB transformers that could explain those results?
Thank you!
We just tested 2 PCB transformers: ratio, winding resistance, PCB dielectric breakdown and insulation test (megger @ 1kV).
All the tests gave good results on both transformers, but the insulation tests we're pretty low on -both- transformers primary side (about 8 to 9 MegOhm for a 25kV primary side).
The test instrument was working well because we tested surge arresters minutes later and they gave high results. The tests were indoor and the humidity level was not high.
Is there any special conditions or internal configuration in PCB transformers that could explain those results?
Thank you!






RE: PCB transformers standards
RE: PCB transformers standards
What was the dielectric strength of the oil? Insulation test is not the measure of oil's dielectric strength.
RE: PCB transformers standards
RE: PCB transformers standards
Zogzog: The voltage was applyed for 1 minute. I know the voltage is not high, but that doesn't explain why we got those results. The polarization index was not calculated.
By the way, all cables were disconnected during the test.
RE: PCB transformers standards
RE: PCB transformers standards
What was the condition of transfomers before the test? Were they in service?
Why was the test perfromed?
How old are the units? Winding configurations-delta-wye etc?
What was the last time the same test was done?. Is there any history or trending data for the same units? How do they compare?
Wye- connected windings could have tapered insulation (just a guess, I am not a trasfromer manufacturing expert)and if the leads at star point are still connected together, it could give distorted results. I have seen that happening in a old generator windings.
My hunch is this is just an old tranformer and its insulation, somewhere on winding, leads or bushings etc., is deteriorated.
RE: PCB transformers standards
on high or low voltage side. All tests conducted at 1 KV.
RE: PCB transformers standards
The units are about 30 years old and are delta-wye. We have no history about earlier testing.
Unclebob: MB told me the same thing, but there was no clear explanation to this. I was just wondering if someone else could explain why PCB transformers always seem to have those results. And by the way, PL would like to have your e-mail address so we can have news from you! You know ours, send it there if you want!