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The armature current of a series motor is 60 A when on full-load. If the load is adjusted to that this current decreases to 40 A, find the new torque expressed as a percentage of the full-load

The armature current of a series motor is 60 A when on full-load. If the load is adjusted to that this current decreases to 40 A, find the new torque expressed as a percentage of the full-load

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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4 The armature current of a series motor is 60 A when on full-load. If the load is adjusted to that this current decreases to 40 A, find the new torque expressed as a percentage of the full-load torque. The flux for a current of 40 A is 70% of that when the current is 60 A. [46%] 5 A 4-pole, d.c. shunt motor has a flux per pole of 0.04 Wb and the armature is lap-wound with 720 conductors. The shunt field resistance is 240 Q and the armature resistance is 0.2 Q. Brush contact drop is 1 V per brush. Determine the speed of the machine when running (a) as a motor taking 60 A and (b) as a generator supplying 120 A. The terminal voltage in each case is 480 V. [972 r.p.m.; 1055 r.p.m] A 25-kW shunt generator is delivering full output to 400-V bus-bars and is driven at 950 r.p.m. by belt drive. The belt breaks suddenly but the machine continues to run as a motor taking 25 kW from the bus-bars. At what speed does it run? Take armature resistance including brush contact resistance as 6. 0.5 Q and field resistance as 160 Q. [812.7 r.p.m.]
Transcribed Image Text:4 The armature current of a series motor is 60 A when on full-load. If the load is adjusted to that this current decreases to 40 A, find the new torque expressed as a percentage of the full-load torque. The flux for a current of 40 A is 70% of that when the current is 60 A. [46%] 5 A 4-pole, d.c. shunt motor has a flux per pole of 0.04 Wb and the armature is lap-wound with 720 conductors. The shunt field resistance is 240 Q and the armature resistance is 0.2 Q. Brush contact drop is 1 V per brush. Determine the speed of the machine when running (a) as a motor taking 60 A and (b) as a generator supplying 120 A. The terminal voltage in each case is 480 V. [972 r.p.m.; 1055 r.p.m] A 25-kW shunt generator is delivering full output to 400-V bus-bars and is driven at 950 r.p.m. by belt drive. The belt breaks suddenly but the machine continues to run as a motor taking 25 kW from the bus-bars. At what speed does it run? Take armature resistance including brush contact resistance as 6. 0.5 Q and field resistance as 160 Q. [812.7 r.p.m.]
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