T12 DC Generators - Tutorial PDF

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EE3010EllectricalDeviccesandMach hinesbyLeeP PH

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EE3 3010ELECTR RICALD DEVIC ESANDMA CHINEES T UTORIAL122‐DCG Generrators Q1. The magnetisation Q n curve of a 120-V, 10 0-kW, 1800-rpm DC m achine is given g below. The armature and a field win n ding resisstances of the t machin e are 0.20 ohm and 18 ohm ms, respectively. The e field windding has 1000 turns// pole. The field h a rheosstat of 0-15 ohms. The e rotational losses of the machinee are circuit also has es as a sep p arately-exccited generator with a field 650 W. The DC machi ne operate circuit voltag ge of 130 V. Calculate a) Thhe field rh heostat sett ting to ob btain the rated volta age at no--load co ondition. b) Thhe field rhe eostat sett ng when the t genera ator supplie es power to 80 in candescent lamps of 100 W eacch at rated terminal v oltage. Neglect arrmature rea action. c) Th he efficienccy of the generator for the above load condittion. [ Ans :(a) 14 4.5 ohms (b) 5.64 ohm s (c) 78.0 02 %]

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EE3010ElectricalDevicesandMachinesbyLeePH 

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Q2. The DC machine in Q 1 is now operated as a shunt-connected DC generator. Determine a) The field rheostat setting to obtain the rated voltage at no-load condition. b) The terminal voltage when the generator delivers an armature current of 50 A. Neglect armature reaction. Use the field rheostat setting as obtained in (a). c) The input shaft torque and efficiency of the generator for the above load condition. [ Ans :(a) 12 ohms (b) 105 V (c) 33.95 N-M, 76.28 %]

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