Topic 5-ward Leonard System 4i3b4v

Topic 5:

Prepared by: Engr. ARJUN G. ANSAY, EE PhD Professor, TUP-IRTC

Objectives: At the end of the discussion, the participants should be able to: 1. Familiarized the Ward-Leonard System of speed control; 2. Identify the different components of Ward-Leonard System and their functions.

Contents: 1. Content Principle of DC Motor Speed Control 2. Methods of DC Motor Speed Control 3. The Ward-Leonard System Principle

Principle of DC Motor Speed Control The speed “n” of a DC Motor is defined by the following equation: E – Ia ( Ra + Rb ) n= k Ø Where: n Ø E Ia Ra Rb

= = = = = =

speed of DC Motor magnetic flux impressed voltage armature current armature resistance brush resistance

Methods of DC Motor speed control: 1. Field Control

This is a method of controlling the speed by changing the magnetic flux Ø in equation

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 supply the DC Motor thru the used of Separately Excited DC Generator.

Components of Ward-Leonard System: 1. 2. 3. 4.

3Ø – induction motor Separately excited DC Generator Separately excited DC Motor Load (DC Generator)

Block diagram of Ward-Leonard System:

Where: 3Ø = three phase induction motor G1 = separately excited DC Generator M = separately excited DC Motor G = 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.

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 kind attention