Reverse energising the stepdown transformer for Step up purpose ????
Reverse energising the stepdown transformer for Step up purpose ????
(OP)
Is it possible to use a stepdown transformer (11/.4kV ) ,1MVA transformer can be used for step up transformer from .4 to 11kV. If yes ,What are the precaution to be consider such as changing the CT polarity of the primary side etc ?????






RE: Reverse energising the stepdown transformer for Step up purpose ????
RE: Reverse energising the stepdown transformer for Step up purpose ????
Tecnically speaking there is no issue in back charging a transformer except that it's inrush current will be now be quite high in term of amperage as the inrush current could be in order of upto 6 times of the full load current.
HiSet
RE: Reverse energising the stepdown transformer for Step up purpose ????
Regarding the inrush issue:
Inrush currents can be quite high if energized from any side, (primary side or secondary side) but the inrush multiplier tends to be higher if the transformer is energized from the secondary side. See also the comments of cuky2000 in thread238-101496
Depending on the kind of protection you use - especially if you have elements that operate in a few cycles - you might find a trip. What kind of protective devices do you use on the transformer?
Regarding the CT-issue:
Nothing I am aware of, do not see any problem.
RE: Reverse energising the stepdown transformer for Step up purpose ????
RE: Reverse energising the stepdown transformer for Step up purpose ????
Thanks rrghunath ,
What kind of problem would encounter by not having earth reference on the 11kV Side .I have only O/C protection and Eearth fualt indicator on the Ring IN / Ring Out feeder ofthe RMU which is feeding the 11/.4 kV transformer. Any kind ofadditional protection we should consider??? Relay polarity would n't be an issue as the RMU is having self powered MICOM P124 O/C relay ???
High inrush current would be an issue ???
RE: Reverse energising the stepdown transformer for Step up purpose ????
If you will make the synchronization from the HV side, than you may start the generator when the genset breaker is already closed to the transformer.
RE: Reverse energising the stepdown transformer for Step up purpose ????
With no earth reference, the system is prone to over voltages and resultant damage and also it will be a safety hazard considering that the 11kV OHLs run in the city (as earth faults in the system go undetected). I think this will not be permitted by the statutory authorities in your area.
If the 11kV network is a private one, then you may go ahead with the plan but you need to introduce residual voltage sensing type earth fault protection on 11kV side.
High inrush currents when the transformer is energised from low voltage side can cause unacceptably high voltage dips in the low voltage system. This, however depends on the sources available (or how strong is the system) in low voltage system.
If the 11kV system is a ring network (as mentioned) and has some more sources in addition to the subject one, you will have to consider synchronisation requirements as suggested by habor.
RE: Reverse energising the stepdown transformer for Step up purpose ????
I read about this very application at an airfield where 415V at a high kVA was required about a mile from the main substation. The designers installed two distribution transformers back-to-back and thus avoided all the volt drop problems associated with LV distribution.
A neat solution.
RE: Reverse energising the stepdown transformer for Step up purpose ????