Overview
Closeup |
A self starting induction motor that has a rotor and cage operates as an
induction motor when starting and as a synchronous motor when the motor
reaches synchronous speed with the poles of the permanent magnets. Self
starting type permanent magnet motors, often used in industrially or in
household appliances, do not require a starting device while providing
high-efficiency.
Analyzing the current induced in the rotor bars is important because the
induced current essentially determines the performance when the motor operates
as an induction motor. For this reason, it is important to evaluate the
current that is induced in the self starting type permanent magnet motor.
This example presents the use of a magnetic field analysis to obtain the
current density distribution and the slip versus torque curve of a self
starting type permanent magnet motor. |
Current Density Distribution
The current density distribution at a 0.8 slip is indicated in Fig. 1.
If the slip is large, the motor operates as an induction motor. The induced
current largely affects the torque characteristics because the torque is
produced by the rotating magnetic field produced in the coils and the current
induced in the rotor and cage. |
Closeup |
Flux Lines
Closeup |
The flux lines at a 0 slip is indicated in Fig. 2.
If the slip is 0, the motor operates as a synchronous motor. The torque
is produced by the attractive force of the permanent magnetic and the reactance
magnetic flux because the self starting type permanent magnet motor operates
as an IPM motor. |
Slip vs. Torque Curve
The slip versus torque curve is indicated in Fig. 3.
The torque of the self starting type permanent magnet motor gets smaller
as the slip gets larger, reaching a maximum torque at a 0.4 slip. |
Closeup |
|
