Transformer Inrush
Transformer Inrush
(OP)
I have never run into this scenario before so I thought I would double check:
I have a 2400V service that feeds a Delta Delta 2000KVA 2400V/12470V step up transformer that is connected in series directly to a Delta Wye 1500KVA 12470/4160V transformer (This was done this way due to transformer availability and is a temporary installation.)
Since I will be energizing both transformers at the same time will I still assume I will only see the inrush of the first transformer only at the primary of 2400V/12470V? I am making sure the fusing is sized properly and it is sized only for the 2000KVA 2400V/12470V.
I have a 2400V service that feeds a Delta Delta 2000KVA 2400V/12470V step up transformer that is connected in series directly to a Delta Wye 1500KVA 12470/4160V transformer (This was done this way due to transformer availability and is a temporary installation.)
Since I will be energizing both transformers at the same time will I still assume I will only see the inrush of the first transformer only at the primary of 2400V/12470V? I am making sure the fusing is sized properly and it is sized only for the 2000KVA 2400V/12470V.






RE: Transformer Inrush
But why would you want to do this? Can't you open the connection between the two transformers?
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)
RE: Transformer Inrush
RE: Transformer Inrush
RE: Transformer Inrush
RE: Transformer Inrush
Wow!, should have called me, could have doen 2400V/4160V in a week easy. I am trying to wrap my mind around the inrush on these in series, Seems the inrush on the 2nd one would cause similar inrush on the first one as energizing one transfomrer with some loads, which I have done many times without a problem.
Any of the smart guys on here have a forumla for calculating this inrush? I am curious to what it would be.
RE: Transformer Inrush
Is this a temporary installation? The inrush will be difficult to determine - better have some extra fuses on hand - in various sizes.
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)
RE: Transformer Inrush
The decay of the asymmetrical dc component of the first transformer's inrush is affected by connected load. The second transformer is that load and will result in a quicker decay. Meanwhile, the voltage at the first transformer's secondary won't rise instantaneously (like closing a disconnect) due to the inrush and impedance of the first transformer. The second transformer will see its input voltage ramp up over a couple of cycles which will help demagnetize its core's residual flux. Back in my utility days, our substations consisted of transformers followed by separate LTC regulators. Nobody ever gave a second thought to picking up both from the transformer high side switch and I've never heard of a problem.
But as dpc suggests, bring extra fuses.
RE: Transformer Inrush
RE: Transformer Inrush
This is temporary.
RE: Transformer Inrush
Thanks for the discussion,
RE: Transformer Inrush
If you already have differential protection, there is not a lot to be gained by dialing down the primary instantaneous to the razor's edge of tripping on inrush.
For what it's worth, we recently had a case of nuisance tripping on a 15 MVA transformer with a GE SR-750 set to 12X rated current. We had to increase it to 15X.
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)
RE: Transformer Inrush
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla