L 39 TB ET EE NPTEL

Module
9
DC Machines
Version 2 EE IIT, Kharagpur

Lesson
39
D.C Motors
Version 2 EE IIT, Kharagpur

Contents
39 D.C Shunt Motor (Lesson-39)

4

39.1

Goals of the lesson ……………………………………………………………….. 4

39.2

Introduction ………………………………………………………………………. 4

39.3

Important Ideas……………………………………………………………………. 5

39.4

Starting of D.C shunt motor. ……………………………………………………… 7

39.5

39.6

39.4.1

Problems of starting with full voltage. ………………………………… 7

39.4.2

A simple starter. ……………………………………………………….. 7

39.4.3

3-point starter. …………………………………………………………. 8

Speed control of shunt motor …………………………………………………… 10
39.5.1

Speed control by varying armature resistance. ………………………... 10

39.5.2

Speed control by varying field current. ………………………………... 12

39.5.3

Speed control by armature voltage variation. …………………………. 14

39.5.4

Ward Leonard method: combination of Va and If control. …………… 14

Series motor. …………………………………………………………………....... 15
39.6.1

39.7

39.8

Characteristics of series motor. ………………………………………. 16

Speed control of series motor ……………………………………………………. 18
39.7.1

Speed control below base speed ……………………………………... 18

39.7.2

Speed control above base speed ……………………………………… 19

Braking of d.c shunt motor: basic idea …………………………………………... 20
39.8.1

Rheostatic braking ……………………………………………………. 21

39.8.2

Plugging or dynamic braking …………………………………………. 21

39.8.3

Regenerative braking ………………………………………………… 22

39.9

Tick the correct answer ………………………………………………………….. 23

39.10

Solve the following ………………………………………………………………. 24

Version 2 EE IIT, Kharagpur

39.1 Goals of the lesson
In this lesson aspects of starting and speed control of d.c motors are discussed and explained. At the end principles of electric braking of d.c. shunt motor is discussed. After going through the lesson, the reader is expected to have clear ideas of the following.
1. The problems of starting d.c motors with full rated voltage.
2. Use and selection of variable resistance as a simple starter in the armature circuit of a