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Transformers Inrush above Available S.C.

Transformers Inrush above Available S.C.

Transformers Inrush above Available S.C.

(OP)
Looped medium voltage cable system feeds multiple transformers totaling to approximately 21MVA. The voltage is 25kV and utility available short circuit current at the primary gear is about 3kA. My questions is with respect to transient state during momentary source outage.
The 8 to 12 times FLA of all transformers is above the available short-circuit level. My concern is that due to the weak system, the inrush will be limited below the available short circuit level, but the time required for the units to reach steady state could be above the assumed 0.1sec (6-cycles) period. I am just curious to see how some of you have dealt with modeling or solving this issue. My concern is tripping of loop cable protective device upstream of transformers and their protective device. Are there any recommendations or papers on this subject.  

"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
 

RE: Transformers Inrush above Available S.C.

Well, you certainly won't get more inrush current than you could get short circuit current.  You're in the type of situation where your best bet is to energize the circuit several times while recording the waveform of each inrush so that you have some idea of what it looks like.  Otherwise you'll need to do some serious EMTP modeling before hand if you need to know before the first energization.

RE: Transformers Inrush above Available S.C.

(OP)
Thank you David. I need to know before the first energization. I need to size the fuse for cable protection, but I am having a hard time modeling the transformer inrush on the Time-Current Curve.  When you say EMTP, are you referring to the ElectroMagnetic Modeling Program?  

"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
 

RE: Transformers Inrush above Available S.C.

EMTP=ElectroMagnetic Transient Program.  There are several flavors of EMTP.

RE: Transformers Inrush above Available S.C.

(OP)
Sorry for the confusion, that is what I meant. Thanks again!  

"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
 

RE: Transformers Inrush above Available S.C.

(OP)
Thank you jghrist, this helps. Meanwhile I am waiting for my demo version of EMTP to check it out.  

"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
 

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