Q4.(a)Explain what is meant by the term 'back emf in a dc motor, and what effectdoes back emf have on motor starting (there is no call to describe the actualmotor starter).(b)The method of connecting the field winding and armature determines theclassification of a dc machine. With the aid of diagrams, outline the connectiondifferences between separately excited, series, shunt and compound-wound dcmotors.(c)A DC shunt motor is known to have a field resistance of 902, and armatureresistance 0.40. During a test of the motor, the following values were obtained;Supply voltage 250V, line current 40 Amps and motor speed 1800 revs/min.Determine:i) the field currentii) armature currentiii) the motor back emfiv) the maximum potential power outputv) torque outputvi) the efficiency at this load

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Answered: Explain what is meant by the term 'back…

Explain what is meant by the term 'back emf in a dc motor, and what effect does back emf have on motor starting (there is no call to describe the actual motor starter).

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

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Concept explainers

DC Series Motors

A DC motor is a type of electric motor which converts electric energy into mechanical energy. The forces that are produced by the magnetic field are what those common types of motors rely upon. Either electro-mechanical or electronic, all types of DC motors have some internal mechanism to change the current direction in part of the DC motors. As the DC motors could be powered from existing DC lighting power distribution systems, these motors were the first form of motors widely used. By changing the strength of the current in its field winding or by using a variable supply voltage, the speed of the DC motors can be controlled over a wide range.

Question

Q4.
(a)
Explain what is meant by the term 'back emf in a dc motor, and what effect
does back emf have on motor starting (there is no call to describe the actual
motor starter).
(b)
The method of connecting the field winding and armature determines the
classification of a dc machine. With the aid of diagrams, outline the connection
differences between separately excited, series, shunt and compound-wound dc
motors.
(c)
A DC shunt motor is known to have a field resistance of 902, and armature
resistance 0.40. During a test of the motor, the following values were obtained;
Supply voltage 250V, line current 40 Amps and motor speed 1800 revs/min.
Determine:
i) the field current
ii) armature current
iii) the motor back emf
iv) the maximum potential power output
v) torque output
vi) the efficiency at this load

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