Electrical Engineering XYZ MCQs
In Ward-Leonard system, the lower limit of the speed imposed by;
- Armature resistance
- Residual magnetism of the generator
- Field resistance
- None of above
Correct answer: 2. Residual magnetism of the generator
Explanation:
In a Ward-Leonard system, the lower limit of the speed is primarily imposed by the residual magnetism of the generator.
The Ward-Leonard system is a method of controlling the speed of a DC motor. It typically consists of a DC generator driven by a prime mover (such as an electric motor), a motor-generator set, and the DC motor that needs speed control.
The residual magnetism of the generator refers to the small amount of magnetic flux that remains in the generator’s field poles even when the generator is not operating. This residual magnetism plays a crucial role in initiating the generation of electric power when the generator starts up.
In the Ward-Leonard system, the generator produces a variable voltage, and the motor-generator set adjusts this voltage to control the speed of the connected DC motor. The residual magnetism sets the lower limit for the generator’s voltage output when it starts generating power. If the residual magnetism is insufficient, the generator might not produce enough voltage to initiate the motor-generator set and drive the DC motor.
Therefore, the lower limit of the speed in a Ward-Leonard system is imposed by the residual magnetism of the generator. The other options (armature resistance, field resistance, and none of the above) are not directly related to setting the lower limit of the speed in this context.