Out of the 800kw connected load, not all may be running at once. You need to figure out the maximum concurrent load, plus a reserve for starting any motor along with whatever other loads are already running at the time. This can be complicated.
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With 800kw of connected load, it is very surprising to see only 185kw MD. (Why so much idle equipment?)
What is the "moulding M/c"? I understand "chiller compressor," but what is the "auxiliary"? These equipments should have current ratings (or kw ratings that with voltage can be converted to current ratings).
As mentioned before, you add up the current ratings of all equipment that could be running at one time, plus the starting current of the largest motor that might then be started. This gives the total load that the DG must handle. (All of this must be converted to uniform units, such as amperes, kw, or kva.)
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Divide the kVA rating of the generator by the terminal voltage.
Of what significance is this number to the selection of cables and protective devices?
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