20. The number of pole pairs of a 12 kW, 50 Hz synchronous generator runs at a s
ID: 2293174 • Letter: 2
Question
20. The number of pole pairs of a 12 kW, 50 Hz synchronous generator runs at a speed of 3000 r.p.m. 1 b) 6 21. The magnetic field in an induction motor is produced a) Using external DC source b) By induction c) Using brushless exciter on the shaft d) using external DC source or brushless exciter on the shaft 22. The frequency of the voltage obtained from 18 kW, 4 pole, 1800 r.p.m. synchronous generator is a) 50 Hz b) 10 Hz c) 60 Hz d) 360 Hz 23. When a synchronous generator, with a salient rotor, is loaded with a resistive load the output voltage will differ from the armature induced voltage a) Because the PF is unity b) Due to the reduction in the generator speed c) Due to the Impedance of the field coils d) Due to variation in the airgap reluctance 24. The voltage and frequency of an infinite bus-bar are a) Fixed regardless of how much real power (P) drawn from or supplied to it b) Fixed regardless of how much reactive power (Q) drawn from or supplied to it c) Fixed regardless of how much P or Q drawn from or supplied to it d) Fixed regardless of how much P or Q drawn from 25. Theoretically, the maximum output power Pow of a synchronous generator is attained, if the load angle 8 is a) ?/3 b) /2 c) ? d) ?/4 26. The phasor diagrams for leading PF operation of a synchronous generator is a) b) d)Explanation / Answer
20) p = 60 * f / n = 60*50 / 3000 = 1 pole pair
21) option d
22) f = p*n / 60 = 2 * 1800 / 60 = 60 Hz ( 2 pole pair = 4 pole)
23) option a
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