Core and Shell units in the same bank
Core and Shell units in the same bank
(OP)
Our company has an existing bank of (4) 1-phase shell-form transformers, 500kV - 345kV - 34.5kV, 120 MVA (OA), manufactured by Westinghouse in the 1970's. We need to replace two of the four units. We are reviewing bid proposals, and the current low-evaluted bidder proposes to supply core-form transformers with the same tap voltages, capacities, impedances, etc as the existing shell-form. Do you have any experience mixing shell and core form units in the same bank? Is there any reason this is not advisable? Any help will be greatly appreciated. Thank You, in advance....






RE: Core and Shell units in the same bank
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RE: Core and Shell units in the same bank
RE: Core and Shell units in the same bank
At any rate it would seem that the externally measurable parameters are all that matter. Same voltage ratings, (ratios and taps(), same MVA ratings. The only other thing I can think that might be important is similar impedance.
I'm remembering there are some zero-sequence difference between shell and core form 3-phase transformers but not an issue for your single-phase transfomrers connected as three phase.
I may be way off base though. I hope you get some other comments.
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RE: Core and Shell units in the same bank
The newer transformers might have enough in the way of better efficiency that replacing 3 of the units might actually save you some money. You would then use 1 old unit as the in place spare and use the other 2 elsewhere.
I have seem some 3 wire wye primary 4 wire delta secondary distribution banks where 2 of the transformers were say 1/2 the size of the middle transformers. However, 120/240 volt 4-wire delta systems are not intended to be fully balanced systems from a load or source impedance standpoint.
RE: Core and Shell units in the same bank
Core form transformer is supposed to be taller and the other one broader. You may like to check out the GA. Afterall, for any replacenent, the identicality in dimensions is important, more so, when you want to mix and match the two types of single phase transformer units.
raghunath_n00@rediffmail.com
RE: Core and Shell units in the same bank
RE: Core and Shell units in the same bank
Physical dimension differences are likely no matter what you buy. They will obviously have to fit in the space available, but I'm sure you have assured yourself of that.