150619-1956 EDT
A sample set of calculated curves for an induction motor are shown on p 213 in Fig. 13-12 of "Alternating-Current Machinery", by Bailey and Gault, 1951, McGraw-Hill.
Above 50% load power factor and efficiency are moderately flat and greater than 80%. These are calculations for a 35 HP rated motor of the 1951 time period. PF is about 0.27 at no load, and about 0.95 at 35 HP. At 50% load PF is about 0.87 .
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