A starting resistance is inserted at the starting in an induction moto...
Explanation:
In both induction motors and DC motors, a starting resistance is inserted at the beginning of the motor circuit. However, the reasons for doing so differ between the two types of motors.
a) Induction Motor:
The starting resistance is inserted in an induction motor to control the starting torque. When an induction motor is initially started, it requires a high torque to overcome the inertia of the rotor and bring it up to the running speed. By inserting a starting resistance, the starting current is limited, which in turn limits the starting torque. This is necessary to prevent excessive mechanical stress on the motor and the connected load. Once the motor has started and reached a certain speed, the starting resistance is gradually reduced or completely removed to allow full power to the motor.
b) DC Motor:
In a DC motor, the starting resistance is inserted to avoid a large starting current. When a DC motor is initially started, it exhibits a very low resistance, which results in a high starting current. This high current can cause damage to the motor windings and other components. By inserting a starting resistance, the current is limited, preventing excessive current flow and potential damage. Once the motor has started and reached a certain speed, the starting resistance is gradually reduced or completely removed to allow full power to the motor.
c) Limiting Starting Speed:
The starting resistance is not inserted to limit the starting speed of the motor. Instead, it is used to control the starting torque or limit the starting current, as explained above.
Conclusion:
To sum up, the correct answer is option 'A' - the starting resistance is inserted at the beginning of an induction motor to control the starting torque, while in a DC motor, it is done to avoid a large starting current. The starting resistance helps in preventing excessive mechanical stress and damage to the motor and its components during the starting process.
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