Why are external resistances connected to the rotor circuit of a slip ring induction motor during starting?
To significantly increase the starting torque
To understand why external resistances are connected to the rotor circuit of a slip ring induction motor during starting, let's delve into the operation and requirements of such motors.
A slip ring induction motor is a type of induction motor where the rotor is wound and connected to external resistances via slip rings. This configuration allows for greater control over the motor's starting characteristics.
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Purpose of External Resistances: During the startup of an induction motor, the primary objective is to manage the starting current and starting torque.
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Starting Torque: The starting torque of the motor can be significantly increased by adding external resistances to the rotor circuit.
This is because adding resistance increases the rotor circuit resistance, thereby improving the torque and enabling the motor to start under a heavy load.
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Controlled Current: By adding resistance, the amount of rotor current is controlled, thus reducing the impact of high starting current on the power supply and ensuring a smoother operation.
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Reasoning Against Other Options:
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Reduce Stator Frequency: External resistance in the rotor does not affect the frequency of the stator. The frequency is determined by the supply and the speed of the rotor, which relates to slip.
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Eliminate Iron Core Losses: Iron losses occur in the stator due to changing magnetic fields and are not significantly affected by rotor resistance.
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Decrease Supply Voltage: Rotor resistance does not alter the supply voltage, which is controlled externally, independent of the rotor circuit.
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The correct and most relevant reason for adding external resistances is: To significantly increase the starting torque.
Similar Questions
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Which type of rotor consists of a cylindrical laminated core with parallel slots for carrying rotor conductors?
The speed of an induction motor decreases with the increase in:
Direct Online Starters are generally used with motors of:
If a 3-phase 100 Hz induction motor has a slip of 4%, then what will be the frequency of motor induced emf?
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