Table of Contents
- Definition of Ward Leonard Speed Control System
- Construction and Diagram
- Working Principle
- Advantages
- Disadvantages
- Applications
- SSC JE Previous Year MCQs on Ward Leonard System
Definition of Ward Leonard Speed Control System
The Ward Leonard Speed Control System is an electrical drive system used to control the speed of a DC motor over a wide range with excellent speed regulation and smooth operation. It employs a motor-generator set to provide a variable voltage to the motor armature, enabling precise speed control.
Construction and Diagram
The Ward Leonard system mainly consists of three parts:
- Prime Mover: Usually an AC motor or diesel engine driving the generator.
- DC Generator (G): Converts mechanical power from the prime mover into variable DC voltage.
- DC Motor (M): Receives variable voltage from the generator to control speed.
Construction Diagram:
In the diagram above, the speed of the DC motor can be varied by controlling the field excitation of the DC generator, which changes the output voltage and hence motor speed.
Working Principle
The principle of the Ward Leonard system is based on varying the armature voltage of the DC motor to control its speed. Here's how it works step-by-step:
- The prime mover drives the DC generator at a constant speed.
- The output voltage of the generator depends on the field current supplied to it.
- By adjusting the generator's field current using a rheostat or a controller, the output voltage varies.
- The variable DC voltage from the generator armature is supplied to the motor armature.
- Changing the motor armature voltage changes the speed of the motor according to the speed-voltage relationship.
This system provides smooth and wide-range speed control from zero to above the rated speed.
Advantages
- Provides smooth and stepless speed control.
- Wide speed control range (from zero to above rated speed).
- Good speed regulation under varying loads.
- Reversing direction is easy by reversing generator or motor connections.
- High starting torque.
Disadvantages
- Complex and bulky due to separate motor-generator set.
- High maintenance cost because of mechanical parts.
- Low overall efficiency due to multiple energy conversions.
- Expensive installation and running cost.
- Not suitable for low-power applications.
Applications
- Elevators and hoists requiring smooth speed control.
- Cranes and heavy-duty traction systems.
- Steel rolling mills and machine tools.
- Paper mills and textile industries.
- Any industrial drive needing precise speed control over a wide range.
SSC JE Previous Year MCQs on Ward Leonard System
Here are some important MCQs from SSC JE exams related to the Ward Leonard system:
- Q: What is the main purpose of the Ward Leonard system?
Options:
(a) Control speed of AC motor
(b) Control speed of DC motor
(c) Control voltage of generator
(d) None of the above
Answer: (b) Control speed of DC motor - Q: In Ward Leonard system, speed control is obtained by:
(a) Varying armature voltage of motor
(b) Varying field current of motor
(c) Varying field current of generator
(d) Varying supply frequency
Answer: (c) Varying field current of generator - Q: The Ward Leonard system is preferred because:
(a) It is cheap
(b) It provides smooth speed control
(c) It requires less maintenance
(d) None of the above
Answer: (b) It provides smooth speed control - Q: Which of the following is NOT an advantage of Ward Leonard system?
(a) Good speed regulation
(b) Wide speed range
(c) High efficiency
(d) Easy reversing
Answer: (c) High efficiency
Prepare well with these questions and concepts for SSC JE and other competitive exams!