- Ward Leonard Method Definition: The Ward Leonard method is defined as a speed control system for DC motors using a variable voltage supplied by a motor-generator set.
- Basic Connection Diagram: The system involves a DC motor (M1) powered by a generator (G) driven by another motor (M2), with speed controlled by adjusting the generator’s output voltage.
- Advantages: This method offers smooth and wide-range speed control, bidirectional control, uniform acceleration, good speed regulation, and regenerative braking.
- Disadvantages: The system is costly, inefficient when lightly loaded, large, heavy, noisy, and requires frequent maintenance.
- Applications: The Ward Leonard method is used in applications needing precise and sensitive speed control, such as cranes, elevators, steel mills, and locomotives.
Ward Leonard control system is introduced by Henry Ward Leonard in 1891. Ward Leonard method of speed control is used for controlling the speed of a DC motor. It is a basic armature control method. This control system is consisting of a DC motor M1 and powered by a DC generator G. In this method the speed of the DC motor (M1) is controlled by applying variable voltage across its armature. This variable voltage is obtained using a motor-generator set which consists of a motor M2 (either AC or DC motor) directly coupled with the generator G. It is a very widely used method of speed control of DC motor.
Principle of Ward Leonard Method
Basic connection diagram of the Ward Leonard speed control system is shown in the figure below.
The speed of motor M1 is to be controlled which is powered by the generator G. The shunt field of the motor M1 is connected across the DC supply lines. Now, generator G is driven by the motor M2. The speed of the motor M2 is constant.
When generator G’s output voltage is fed to motor M1, the motor starts rotating. Varying the generator’s output voltage changes the motor’s speed.
By controlling the generator’s output voltage, the speed of motor M1 can be managed. A field regulator connected across the generator with the DC supply lines controls the field excitation. The direction of motor M1 can be reversed by adjusting the generator’s excitation current using a reversing switch, while the motor-generator set continues running in the same direction.
Advantages of Ward Leonard System
- It is a very smooth speed control system over a very wide range (from zero to normal speed of the motor).
- The speed can be controlled in both the direction of rotation of the motor easily.
- The motor can run with a uniform acceleration.
- Speed regulation of DC motor in this Ward Leonard system is very good.
- It has inherent regenerative braking property.
Disadvantages of Ward Leonard System
- The system is very costly because two extra machines (motor-generator set) are required.
- Overall efficiency of the system is not sufficient especially if it is lightly loaded.
- Larger size and weight. Requires more floor area.
- Frequent maintenance.
- The drive produces more noise.
Application of Ward Leonard System
This Ward Leonard method of speed control system is used where a very wide and very sensitive speed control is of a DC motor in both the direction of rotation is required. This speed control system is mainly used in colliery winders, cranes, electric excavators, mine hoists, elevators, steel rolling mills, paper machines, diesel-locomotives, etc.
