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Due to which of the following, The high starting current is flow in the 3-Phase Induction Motor?
At starting, S=1
At Starting, Eb=0 (Back EMF in rotor winding)
At Starting, E1=0 (induced EMF of Stator winding)
All of the above
At starting, S=1
The correct answer is A) At starting, S=1. In a three-phase induction motor, when it starts, the slip S is equal to 1, indicating that the rotor is at standstill, which results in maximum current flow.
The correct answer is A) At starting, S=1. In a three-phase induction motor, when it starts, the slip S is equal to 1, indicating that the rotor is at standstill, which results in maximum current flow.
S=NsтАЛNsтАЛтИТNrтАЛтАЛ тАФ represents the slip in an induction motor, where NsтАЛ is synchronous speed and NrтАЛ is rotor speed.
The high starting current occurs because when the motor is initially turned on, the rotor is stationary and the difference between the synchronous speed of the stator field and the rotor speed is maximum. As a result, the slip S is equal to 1, leading to high torque generation and increased current drawn from the supply.
At standstill, the rotor has no induced EMF, thus the armature current is limited only by the stator impedance.
The current flowing during startup can be 5 to 7 times the full load current of the motor.
High starting torque due to maximum current flow.
Reliable operation in various applications where high initial torque is required.
High starting current can lead to voltage dips in the supply system.
Increased heating may occur in the motor windings at startup.
Used in applications requiring high starting torque, such as crushers, conveyors, and hoists.
Widely utilized in industrial setups where heavy loads need to be moved from rest.
Standard starting current value can range from 600% to 800% of the rated current.
Option B is incorrect because at startup, back EMF in rotor winding (EbтАЛ) is zero, but this is not the primary cause of high starting current.
A is correct тАФ At starting, slip S is 1, resulting in maximum current flow in the motor.
Understand the relationship between slip, rotor speed, and starting conditions to effectively tackle induction motor problems.