Asynchronous Induction Motor with Slip‐Ring Rotor
When starting industrial induction motors, different methods are often employed to prevent damages to the motor windings due to high starting currents. Here, we study how the use of rotor slip rings connected to a rheostat—an adjustable resistor—can be used as one such method.
The AIMS Model
For our analysis, we are using the asynchronous induction machine with slip rings (AIMS) model defined in the Modelica.Electrical.Machines
library. The slip rings—which allow for the connection of rotating and stationary electrical devices—are connected to the rheostat, which is shortened shortly after the motor has picked up speed. The simulation of the model is compared to that of an asynchronous squirrel cage induction motor (AIMC), a type of induction motor that does not use slip rings.
The AIMS model as seen in the diagram view in Wolfram SystemModeler. The AIMC model is configured exactly the same, except for the use of the rheostat.
As can be seen in the plots below, the current is much lower when using an AIMS. This behavior is explained by the added resistance to the rotor circuit, which reduces both the rotor and stator currents.
The current drawn when starting the two motors.
Motor speed. Once the rheostat has been shortened, the AIMS reaches its nominal speed.