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Unformatted text preview: S in 3 V L I L = note that although the efficiency of the motor was assumed to remain high at 93% when the motor is half loaded, the power factor becomes very poor at half load. c. Since the motor's frequency is 60 hz, and its stated speed is 1180 rpm, we can assume that the synchronous speed is 1200 rpm, which would mean a 6 pole motor. Alternatively, we can calculate the number of poles at rated speed RPS RPM 60 sec min = RPS 19.333 1 sec = revolutions per second RPS 2 f P = so P 2 f RPS = P 6.207 = poles Obviously, the number of poles must be an even integer, so this is a six pole motor...
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- Spring '12