What is Ward Leonard Method : Advantages & Its Applications

Harry Ward introduced Ward Leonard Control System Method in 1891 for controlling the DC motor speed. This method is a basic armature control method. There are two different types of voltage control methods they are multiple voltage control method and ward Leonard control system methods or armature voltage control. This article discusses the way of achieving the speed control by adjusting the voltage using the Ward Leonard Control System method.

What is Ward Leonard Method?

Definition: The Ward Leonard method of speed control or armature voltage control is basically used in the place wherever highly sensitive speed is being controlled. It is used in elevators, paper machines, electric excavators, diesel-locomotives, cranes, colliery winders, etc.

Ward Leonard Method

The Ward Leonard Method of speed control system consists of the main motor (M1), DC generator (G), and controlled DC motor (M2). The power supply is fed to the armature terminal of the dc machine as well as the shunt field point. The main motor is coupled directly to the dc generator so that the power is directly fed to the controlled dc motor. To control the voltage to the dc generator, the field regulator is used, so by regulating the value from zero to maximum, the dc voltage gets regulated at a stature point. The regulated dc voltage is being fed to the controlled dc motor.

If we want to reverse the action of the dc motor, we have to just reverse the field current of the dc generator. In the case, if we reverse the field current of the dc generator, the motor rotation gets reversed automatically. The reverse direction is being achieved by using the switch RS, the RS is nothing but reverse switch. The Ward Leonard Method of speed control diagram is shown below.

The Ward Leonard Control system is combined with two control strategies they are: armature voltage control and field control. The armature voltage control is being achieved by varying the field of the dc generator. The torque and power characteristics of this system shown in the below figure.

The Ward Leonard control system provides two constant values they are constant horsepower and constant torque. The X-axis is a speed that is divided into two parts i.e from 0 to 100% and above 100%. The speed from 0 to 100% is named as base speed and after 100% is named as above base speed. Similarly, the control strategies are divided into two parts from 0 to 100% is denoted as armature voltage control and above base-speed is denoted as field control.

Case1-Torque Vs Speed

When speed increases from 0 to 100%, then the torque will be maintained as constant and when we move speed from 100 to above base speed, in that case, the torque is linearly decreased in armature voltage control. When we vary the field of the controlled dc motor, the torque value will be linearly decreased in-field control.

Case2-Horse Power Vs Speed

In 0 to 100%, the horsepower linearly increases as we increase the value of the base speed and after base speed, the horsepower maintains constant if we increase the speed of the machine.

Applications

Some of the applications of the armature voltage control are

• Mine hoists
• Elevators
• Steel rolling mills
• Paper machines
• Diesel locomotives
• Cranes

The advantages of armature voltage control are

• Power wastage is less because no starting rheostat is used
• Wide range, accurate, and bidirectional speeds are obtained easily
• The speed regulation is good