I think the 600 just comes from combining up the efficiency, PF, √3, and KW to HP conversions into an empircal constant given in equation 13.5 on page 277. If you want to make some assumptions simialr to Kovz above, say efficiency of 0.95 and Pfactor of 0.9 the KVA in then is (500*0.746)/(0.95...