Electrical Engineering XYZ MCQs
Armature resistance control method is used for the:
- Below rated speed
- Above rated speed
- Both of the above
- None of the above
Correct answer: 1. Below rated speed
Explanation:
Armature resistance control is a method used in DC motor speed control, primarily for controlling the speed of a motor below its rated speed.
Here’s how it works:
- Voltage Drop: By increasing the resistance in the armature circuit, the voltage drop across the armature increases. This reduces the effective voltage applied to the armature, resulting in a decrease in speed.
- Effect at Below Rated Speed: At speeds below the rated speed, the back EMF (electromotive force) generated by the motor is lower than the applied voltage. Therefore, reducing the effective voltage by increasing armature resistance decreases the motor speed.
- Above Rated Speed: However, this method is not effective for controlling speeds above the rated speed. At speeds above the rated speed, the back EMF generated by the motor is higher than the applied voltage. Therefore, increasing armature resistance would decrease the voltage even further, which could lead to a loss of torque and poor motor performance.
So, armature resistance control is primarily used for controlling the speed of a DC motor below its rated speed. Above the rated speed, other methods such as field weakening or flux weakening are typically employed for speed control.