Understanding Electrical Machines: Queries & Answers

[installer2001]

Hello Guys,
I am a beginner in the field of Electrical well i have certain queries to ask from u genius guys

1):WHY THERE IS NO BACK EMF in 3-phase INDUCTION MOTOR
2):WHY WE REMOVE RHEOSTAT after 3-5 seconds of STATRTING OF 3-pahse INDUCTION MOTOR.
3):IF WE APPLY SINGLE PHASE ,THEN HOW SINGLE PHASE ROTATE WHEN THERE IS NO MAGNETIC FIELD IS PRESENT
4);IF DC applied ON STATOR OF 3-phase INDUCTION MOTOR WHAT IS EFFECT ON TORQUE COMPONENT



PLz do reply bcoz i am very keen of acquiring knowledge regarding electrical machines
Thz in Advance

 

[Averagesupernova]

Hello Guys,
I am a beginner in the field of Electrical well i have certain queries to ask from u genius guys

1):WHY THERE IS NO BACK EMF in 3-phase INDUCTION MOTOR

There is.

2):WHY WE REMOVE RHEOSTAT after 3-5 seconds of STATRTING OF 3-pahse INDUCTION MOTOR.

There is no requirement that there is a rheostat to start with. I suspect you are referring to some sort of soft-start setup where starting torque is not important.

3):IF WE APPLY SINGLE PHASE ,THEN HOW SINGLE PHASE ROTATE WHEN THERE IS NO MAGNETIC FIELD IS PRESENT

It can't start that way, but it can run that way. It 'appears' that there is a rotating magnetic field.

4);IF DC applied ON STATOR OF 3-phase INDUCTION MOTOR WHAT IS EFFECT ON TORQUE COMPONENT

DC on the stator will cause the heating in the rotor. I would imagine torque would be reduced.

 

[ravenprp]

Hello,

1) The reason for no back EMF in a 3-phase induction motor is due to the design of the motor. In a 3-phase induction motor, the stator winding is connected to a 3-phase AC power supply, which creates a rotating magnetic field. This rotating magnetic field induces a current in the rotor, which creates a torque and causes the motor to rotate. Since the rotor is not connected to an external circuit, there is no back EMF generated.

2) The purpose of the rheostat is to limit the starting current of the motor. As the motor starts, the rotor is not yet rotating and therefore does not create a back EMF. This results in a high current being drawn from the power supply, which can damage the motor. Once the motor starts rotating, the back EMF is generated and the current decreases. Therefore, the rheostat is removed to allow the motor to run at its full speed and reduce the risk of damage.

3) In a single-phase induction motor, the stator winding is connected to a single-phase AC power supply. This creates a pulsating magnetic field, which induces a current in the rotor and causes it to rotate. The pulsating magnetic field is created by the interaction of the stator winding and a small auxiliary winding, which creates a phase shift in the magnetic field. This allows the motor to rotate even though there is no continuous magnetic field present.

4) If a DC voltage is applied to the stator of a 3-phase induction motor, it will not rotate. This is because the stator winding is designed to work with an AC power supply, which creates a rotating magnetic field. A DC voltage will not create a rotating magnetic field, therefore the motor will not rotate. Additionally, applying DC voltage to the stator can damage the motor and should not be done.

I hope this helps answer your questions and increases your understanding of electrical machines. Keep learning and keep asking questions!