Dry type transformers
Dry type transformers
(OP)
Has anybody experienced failure of dry type distribution transformers. If yes any particular reason for failure.
Thanks
Thanks
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RE: Dry type transformers
RE: Dry type transformers
Mike
RE: Dry type transformers
Gunnar Englund
www.gke.org
RE: Dry type transformers
Most failures I have encountered were due to dirt build-up causing overheating or arcing and moisture.
Cast coil primary windings are supposed to cure most of these ills, but apparently it didn't work out well for skogsgurra.
RE: Dry type transformers
(big grin). It wasn't me that made them transformers. An Italian company (now defunct) did. We found out that there were voids between resin and primary windings. That is where ozone built up.
The process was accelerated by the heavy 8000 Hz ringing because the local field strength in the sub-millimetre voids was well over corona inception levels and the 8000 Hz forced a much greater current than the normal 50 Hz would have done.
There was no dirt on these transformer windings (not enough lifetime to collect dirt).
Gunnar Englund
www.gke.org
RE: Dry type transformers
If you enquire for cast resin transformers there is a wide range of prices you will get. but, nothing is fro free. If you choose a cheap one you may end up wizh problems like described here.
RE: Dry type transformers
The paper mill now uses Geafoil (expensive, but proven) dry transformers in that application.
I am not sure that PD testing would have revealed this particular fault. There are identical transformers in another part of the paper mill (without the 8000 Hz ringing) and they have survived. We had a specialist company doing ultrasound PD testing on them - they found nothing.
Gunnar Englund
www.gke.org
RE: Dry type transformers
RE: Dry type transformers
RE: Dry type transformers
Could you give us more detail about the lamination failures? Is it possible to identify it via winding visual inspection?
Thanks in advance !
fvincent
RE: Dry type transformers
How did you find the voids beetween resin and primary windings (inspection, testing)? Were them caused by problems in the manufacturer's vacuum process ?
Thanks in advance !
fvincent
RE: Dry type transformers
As far as I know, usually, there is no indication that a lamination failure could be visually verified (someone please chime in if you think this is incorrect). From the folks I've talked to, it can only be determined via power factor testing, or some other type of insulation testing (not Megger though!).
Mike