Answer / engr. kashif

Induction motors are AC motors and they rely on the principle of Induction thus called induction motors. The stator is given a three phase supply and with the help of the revolving magnetic field produced by it, current is induced in the rotor. This then itself generates a magnetic field opposite to the one generated by the stator. These two fields react with each other to produce rotor movement.

Speed may be controlled either by varying input frequency or by changing the no. of poles of the motor. Obviously changing the no. of poles of the motor is not possible unless u alter the motor design or its a specialized multi winding motor. So we have to settle for the other option i.e. change the input frequency. This can be accomplished with the help of VFD (Variable Frequency Drives). They allow u to control the input frequency and thus the speed of the motor.

how we select the mva rating of the circuit breakers?

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Your B.tech marks is being given in CGPA grade. How is it calculated?

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