Estimating available capacity based on peak demand

[tapankatwala]

Hello,

I wanted to inquire if it is possible to estimate available electrical capacity in an electrical distribution system based on only peak demand information available. For e.g. if an 800A, 347/600V, 3-phase electrical service has a peak demand of 175kW, would it be safe to assume the following calculation to estimate available electrical capacity at unity power factor:

800A x 0.8 = 640A (max. loading)
175kW = 600V x A x 1.732 i.e. A = 168A
Available capacity would be 640A - 168A = 472A.

Would the estimation of available capacity change if there are 600V - 208V step-down transformers downstream of the electrical distribution system?

Thank you.

 

[PHovnanian]

"Would the estimation of available capacity change if there are 600V - 208V step-down transformers downstream of the electrical distribution system?"

No. Not at the 347/600V service point. Your above calculations are correct.
Downstream of each stepdown transformer, the portion of the 175kW total peak load on each will have to be measured and compared to each transformer's and downstream panel/switchgear's capacity. It is possible that the transformers and sub-panels are operating at different load factors now. So an across the board increase to utilize the available service capacity could push one or more subsystem over its limit.