# Induction motor rotor and stator fluxes

• Physicist3
In summary, the stator flux is determined by the input power source and decreases slightly with loading, while the rotor flux is determined by the rotor currents and balances out the stator flux per Ampere's Law. Overall, the stator flux remains nearly constant, but the IR drops increase and the net emf across the stator winding is reduced due to the load.
Physicist3
Hi,

When a load is applied to the rotor of an induction motor, the rotor speed decreases and as a result, the induced currents in the rotor and the torque produced increases due to the relative speed difference between the rotor and the rotating field within the stator. My question is, should the magnitude of the flux remain constant for both the rotor and the stator when load is applied, or should it increase/decrease?

Many thanks.

Your question is ambiguous because "the flux" consists of more than 1 quantity. The stator flux is determined by the input power source, typically constant voltage. Some but not all of it links the rotor. The currents in the rotor generate their own magnetic flux opposing the stator linked flux per law of Lenz. Then some of that rotor flux couples the stator. So it isn't as simple as 1 flux value. When the load is connected, currents in both stator and rotor increase, IR drops increase as well. Overall the motor is modeled like a transformer. The stator flux decreases a little with loading. Any rotor current mmf (amp-turns) is balanced by the stator mmf per Ampere's Law. Stator flux is nearly constant since any tendency for stator flux reduction by rotor currents is balanced by increased stator current. But IR drops increase and flux in stator is reduced since the net emf across the stator winding is reduced due to IR drop.

Did I help or make things worse?

Claude

## 1. What is an induction motor rotor and stator?

An induction motor rotor is the rotating part of the motor, typically made of copper or aluminum bars and connected to the shaft. The stator is the stationary part of the motor, consisting of a core and windings that produce a magnetic field.

## 2. How do the rotor and stator fluxes interact in an induction motor?

The rotor flux is induced by the stator flux and causes the rotor to rotate, while the stator flux is produced by the stator windings and remains stationary. The interaction between these two fluxes creates the rotational force that drives the motor.

## 3. What is the significance of controlling the rotor and stator fluxes in an induction motor?

Controlling the rotor and stator fluxes is essential for efficient operation of an induction motor. By adjusting the flux levels, the motor's speed, torque, and power output can be controlled to meet the specific requirements of the application.

## 4. How is the rotor flux controlled in an induction motor?

The rotor flux can be controlled through the use of rotor resistance, which is achieved by adding resistance to the rotor circuit. This resistance reduces the rotor current and therefore the rotor flux, allowing for control over the motor's speed and torque.

## 5. How is the stator flux controlled in an induction motor?

The stator flux can be controlled through the use of stator voltage and frequency. By adjusting these parameters, the stator flux can be increased or decreased, allowing for control over the motor's speed and torque. Additionally, advanced control techniques such as sensorless vector control can be used to more precisely control the stator flux and improve motor performance.

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