Electrical

[alan]

Hi.

Can someone please help me with this two questions.

 

1 why the power factor improves as the machine is loaded for a three phase Induction Motor

 

2 And why the torq increases with slip

[marke]

Hello Alan

 

Welcome to the forum.

 

A simplified version of the equivilent circuit of an induction motor comprises a shunt inductor representing the magnetising current and a shunt resistor representing the shaft load.

The magnetising current stays constant and the shaft load current changes with the shaft load.

At no load, the current is inductive so has a low power factor.

At full load, the inductive element remains constant, but the shaft load current is much higher, so the power factor is much better.

 

 

The torque generated by a motor is a function of the magnetic interaction between the stator field and the rotor field. The stator field is determined by the stator winding and the voltage across it. Similarly, the rotor field is determined by the rotor winding and the voltage across it.

The induced voltage in the rotor is a function of the difference in speed (slip) between the stator field and the rotor. As the slip increases, the rotor volts increases, so the strength of the rotor field increases resulting in an increase in the torque.

 

Best regards,

Mark.