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1. A 500 V, 250 kW, long shunt compound generator induces an e.m.f. of 480 V when running at 1000 r.p.m. no load. On full load the spped of the machine drops to 975 r.p.m. the flux increases by 15% and the terminal voltage rises to 500 V. If the series and shunt field resistances are 0.02 ohm and 100 ohms respectively, calculate the armature resistance. Assume a voltage drop of 1V per brush.

1. A 500 V, 250 kW, long shunt compound generator induces an e.m.f. of 480 V when running at 1000 r.p.m. no load. On full load the spped of the machine drops to 975 r.p.m. the flux increases by 15% and the terminal voltage rises to 500 V. If the series and shunt field resistances are 0.02 ohm and 100 ohms respectively, calculate the armature resistance. Assume a voltage drop of 1V per brush.

Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
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1. A 500 V, 250 kW, long shunt compound generator induces an e.m.f. of 480 V when running at 1000 r.p.m. no load. On full load the spped of the machine drops to 975 r.p.m. the flux increases by 15% and the terminal voltage rises to 500 V. If the series and shunt field resistances are 0.02 ohm and 100 ohms respectively, calculate the armature resistance. Assume a voltage drop of 1V per brush. 2. A 250 V shunt generator has a full load armature current of 40 A, under these conditions the losses are: FW = 200 watts, shunt field = 100 watts, core = 260 watts, brush contact = 120 watts, armature copper = 400 watts. For operation at maximum efficiency, when the constant losses are equal to those losses that vary as the square of the load, calculate the maximum efficiency. 3. A series generator having a combined armature and field resistance of 0.4 ohm us running at 1000 rpm and delivering 5.5 kW at a terminal voltage of 110 V. If the speed is raised to 1500 rpm and load adjusted to 10 kW, find the new terminal voltage. Assume the machine is working on straight line portion of magnetization characteristics. 4. The dc shunt generator is connected to a load that draws 28,800 watts, given the armature and shunt field resistance of 0.04 ohm and 48 ohms respectively. If the power delivered in the armature is 106.3% of the power delivered to the load. Calculate the generated e.m.f. of the generator. 5. URS Electrician has a 25 kW series generator used in street lighting has an efficiency of 85 8 when operating at rated load. If the stray power loss is 20 % of the full load loss, calculate the efficiency of the generator when delivering a load of 15 kW, assuming that the stray power loss is substantially constant and the other losses vary as the square of the load.
Transcribed Image Text:1. A 500 V, 250 kW, long shunt compound generator induces an e.m.f. of 480 V when running at 1000 r.p.m. no load. On full load the spped of the machine drops to 975 r.p.m. the flux increases by 15% and the terminal voltage rises to 500 V. If the series and shunt field resistances are 0.02 ohm and 100 ohms respectively, calculate the armature resistance. Assume a voltage drop of 1V per brush. 2. A 250 V shunt generator has a full load armature current of 40 A, under these conditions the losses are: FW = 200 watts, shunt field = 100 watts, core = 260 watts, brush contact = 120 watts, armature copper = 400 watts. For operation at maximum efficiency, when the constant losses are equal to those losses that vary as the square of the load, calculate the maximum efficiency. 3. A series generator having a combined armature and field resistance of 0.4 ohm us running at 1000 rpm and delivering 5.5 kW at a terminal voltage of 110 V. If the speed is raised to 1500 rpm and load adjusted to 10 kW, find the new terminal voltage. Assume the machine is working on straight line portion of magnetization characteristics. 4. The dc shunt generator is connected to a load that draws 28,800 watts, given the armature and shunt field resistance of 0.04 ohm and 48 ohms respectively. If the power delivered in the armature is 106.3% of the power delivered to the load. Calculate the generated e.m.f. of the generator. 5. URS Electrician has a 25 kW series generator used in street lighting has an efficiency of 85 8 when operating at rated load. If the stray power loss is 20 % of the full load loss, calculate the efficiency of the generator when delivering a load of 15 kW, assuming that the stray power loss is substantially constant and the other losses vary as the square of the load.
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