Reference for Backfeed Transformer In-rush
Reference for Backfeed Transformer In-rush
(OP)
I am into a discussion wherein it was proposed to use a step down transformer as a step up transformer (backfeeding). I cautioned the proposal requiring an in-rush investigation to verify whether the system and protective devices can tolerate such higher than normal in-rush. There was a transformer committee: IEEE/PES which provided a tabulated multiples of FLA for backfeeding.
Can someone quote me the section and IEEE/PES document that defines this in-rush phenomena when transformers are deliberately backfed?
Can someone quote me the section and IEEE/PES document that defines this in-rush phenomena when transformers are deliberately backfed?






RE: Reference for Backfeed Transformer In-rush
We have few threads on the topic.
Please try search on the Forum.
Best Regards.
Slava
RE: Reference for Backfeed Transformer In-rush
In thread reference 238-101496, cuky2000 indicated a IEEE/PES reference. I would like to ask what IEEE/PES document number for my further reference.
RE: Reference for Backfeed Transformer In-rush
Cuky has mentioned a diffrence with delta connection and star connection.This is not a universal situation.This change happens due to coupling factor.ie for a YN/d unit excitation current will be same as YN/yn unit when excited from LV.But current will come down by 40 % in a D/yn unit with LV excitation.
RE: Reference for Backfeed Transformer In-rush
Do you have any link or literature that discuss transformer backfeeding?
RE: Reference for Backfeed Transformer In-rush
RE: Reference for Backfeed Transformer In-rush
The winding current is proportional to the mmf, the mmf is proportional to the flux, the flux is inversely proportional to the leakage reactance. And the leakage reactance is proportional to the axial mean length of the winding, ampere turns of the energized winding.
Now since the LV winding is closer to the core, the leakage reactance is lower and if the voltage period during switching-in is zero, then the generated flux will be twice normal in its attempt to integrate with voltage for displacement and there goes the inrush scnenario. If the voltage period during switching-in happened at zero and there is residual magnetism in the core, then it will go even higher than twice...is my understanding now correct?
If the step down transformer LV winding (used as primary)is switched with at voltage zero, with residual magnetism and is connected with load, is the rated load current reflected at the primary going to add up to the in-rush current?
RE: Reference for Backfeed Transformer In-rush
RE: Reference for Backfeed Transformer In-rush
Nightfox,I dont think leakage reactance has anything to do with flux in the core.
Yes.Load current will add up with the inrush current.
Yes.Phenomenon same with the three winding transformer.
RE: Reference for Backfeed Transformer In-rush
RE: Reference for Backfeed Transformer In-rush