1. ...and/or the desire to be capable of some future expansion without needing to change out the transformer, cable, main bus etc., etc. when the time comes. There is a price to pay for that besides just the initial cost of that larger transformer in that there will be slightly higher losses in the larger transformer, but that difference would likely be insignificant compared to a change-out at a later date.

2. Senior Member
Join Date
Nov 2007
Posts
835
Please can you guide me on how 500kVA IS GOOD FOR 450Kw load. I want to know how to arrive at this t/f value
You have to factor in the diversity factor and the power factor.

Transformer size = connected load(in kW)/PF X DF X 1.30

IMO, your 750kVA trafo and CB selection is a result of a power factor of 0.8, a diversity factor of 0.7!
See the math:
transformer size = (476.47/0.8) X 0.7 X 1.3 = 541.98kVA. The nearest size would be 750kVA!

Sizing of the secondary protection cb also depends whether the system is supervised or not (NEC 450.3). 1200A if not supervised and 2000A, if supervised(supervised = only qualified personnel monitor and service the transformer installation is ensured).

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