1. If a 60-Hz synchronous motor is to be operated at 50 Hz, will its synchronous reactance be the same as at 60 Hz, or will it change? (Hint: Think about the derivation of XS .)
2. A 480-V 100-kW 0.85-PF leading 50-Hz six-pole Y-connected synchronous motor has a synchronous reactance of 1.5Ω and a negligible armature resistance. The rotational losses are also to be ignored. This motor is to be operated over a continuous range of speeds from 300 to 1000 r/min, where the speed changes are to be accomplished by controlling the system frequency with a solid-state drive.
(a) Over what range must the input frequency be varied to provide this speed control range?
(b) How large is EA at the motor's rated conditions?
(c) What is the maximum power the motor can produce at the rated conditions?
(d) What is the largest EA could be at 300 r/min?
(e) Assuming that the applied voltage Vf is derated by the same amount as EA , what is the maximum power the motor could supply at 300 r/min?
(f) How does the power capability of a synchronous motor relate to its speed?