Topic 5:

Prepared by:

Engr. ARJUN G. ANSAY, EE PhD

Professor, TUP-IRTC

At the end of the discussion, the

participants should be able to:

1. Familiarized the Ward-Leonard System

Objectives:

of speed control;

2. Identify the different components of

Ward-Leonard System and their

functions.

1. Content Principle of DC Motor Speed

Control

2. Methods of DC Motor Speed Control

Contents:

3. The Ward-Leonard System Principle

The speed “n” of a DC Motor is defined by the following equation:

Principle of DC Motor Speed

Control

n = kE – Ia ( Ra + Rb )

Ø

Where:n = speed of DC MotorØ = magnetic fluxE = impressed voltageIa = armature currentRa = armature resistanceRb = brush contact resistance

Ø

1. Field Control

� This is a method of controlling the speed by

changing the magnetic flux Ø in equation

2. Armature Resistance Control

Methods of DC Motor speed

control:

2. Armature Resistance Control

� This speed control is performed by inserting a

series resistance in the armature circuit.

3. Voltage Control

� This speed control is done by varying the

voltage across the armature circuit of the DC

Motor.

WARD-LEONARD SYSTEM

- is a method of speed control

using voltage as variable to using voltage as variable to

supply the DC Motor thru the

used of Separately Excited DC

Generator.

1. 3Ø – induction motor

2. Separately excited DC Generator

3. Separately excited DC Motor

4. Load (DC Generator)

Components of Ward-Leonard System:

4. Load (DC Generator)

Block diagram of Ward-Leonard System:

Where:

3Ø = three phase induction motorG1 = separately excited DC GeneratorM = separately excited DC MotorG = Load (DC Generator)

Schematic Diagram of Ward Leonard System

�Note:

Frequently, control of generator voltage

is combined with motor field control for

variation in speed.variation in speed.

Advantage:

1. Provide excellent step less speed

control

2. Very wide range of speed.

Disadvantage:

1. High first cost

2. Low over-all efficiency

Thank you for Thank you for

kind attention