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University of the West Indies at Mona - ELETRONICS 1400Dc machine QUESTIONS ( WITH 100% CORRECT COMPLETE SOLUTIONS )

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CHAPTER 25 D.C. MACHINES Exercise 157, Page 446 1. A 4-pole, wave-connected armature of a d.c. machine has 750 conductors and is driven at 720 rev/min. If the useful flux per pole is 15 mWb, determ ... ine the generated e.m.f. Z = 750, c = 2 (for a wave winding), p = 2 pairs, n = 720 60 rev/s and  = 15  10-3 Wb Generated e.m.f. E = 2p nZ c = 3 720 2(2)(15 10 ) (750) 60 2         = 270 volts 2. A 6-pole generator has a lap-wound armature with 40 slots with 20 conductors per slot. The flux per pole is 25 mWb. Calculate the speed at which the machine must be driven to generate an e.m.f. of 300 V. p = 6/2 = 3, lap means c = 2p, Z = 40  20 = 800,  = 25103 Wb, E = 300 V Generated e.m.f., E = 2 p n Z c from which, speed, n =    3    3   E c 300 2p 300 2 p Z 2p 25 10 800 25 10 800      = 15 rev/s or 900 rev/min 3. A 4-pole armature of a d.c. machine has 1000 conductors and a flux per pole of 20 mWb. Determine the e.m.f. generated when running at 600 rev/min, when the armature is (a) wavewound, (b) lap-wound. p = 4/2 = 2, Z = 1000,  = 20103 Wb, n = 600/60 = 10 rev/s (a) For wave wound, c = 2, hence, generated e.m.f., E = 2p n Z 2220 10 3101000 c 2     = 400 V [Show More]

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