Engineering

Electrical EngineeringQ&A LibraryTwo shunt generators operating in parallel supply a total load of 3700 A. Each generator has a field resistance of 60 Ω and an armature resistance of 0.01 Ω. The fields are excited so that the e.m.f. induced in one generator is 440 V and in another 445 V. Find the bus-bars voltage and kilowatt output of each machine.Question

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Q1: Two shunt generators operating in parallel supply a total load of 3700 A. Each generator has a field resistance of 60 Ω and an armature resistance of 0.01 Ω. The fields are excited so that the e.m.f. induced in one generator is 440 V and in another 445 V. Find the bus-bars voltage and kilowatt output of each machine.

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Q2: In a 110 V compound generator, the resistance of the armature, shunt and series windings are 0.06 Ω, 25 Ω and 0.04 Ω respectively. The load consists of 200 lamps each rated at 55 W, 110 V. Find the armature current and e.m.f. generated when the machine is connected (i) long shunt, (ii) short shunt.

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Q3: A 4-pole, wave-wound d.c. machine running at 900 r.p.m. has a commutator of 0.46 m diameter. If the armature current is 90 A, thickness of brush 1.25 cm and the self-inductance of each armature coil is 0.08 mH, calculate the average e.m.f. induced in each coil during commutation. Assume linear commutation and neglect mica thickness.

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Q4: The output of a shunt generator is 24 kW at a terminal voltage of 200 V. Armature resistance = 0.05 Ω and shunt field resistance = 40 Ω. If the iron and frictional losses equal the copper losses at this load, find (i) b.h.p. of the engine (ii) overall efficiency.

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Q5: A shunt generator supplies 190 A at 220 V. Shunt field resistance = 32 Ω. The copper losses = 1.85 kW. The iron and frictional losses are 1450 W. Find (i) e.m.f generated (ii) mechanical input power (iii) armature resistance (iv) commercial efficiency.

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Q6: The resistance of the field circuit of a shunt-excited d.c. generator is 200 Ω. When the output of the generator is 100 kW, the terminal voltage is 500 V and the generated e.m.f. 525 V. Calculate (i) the armature resistance (ii) the value of generated e.m.f. when the output is 60 kW, if the terminal voltage is then 520 V.

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