rotor bar

The rotor bars may be made either of copper or aluminum.

The shape of the rotor bars determines the speed-torque characteristics.

A substantial portion is still in use for the production of rotor bars and extruded section.

This equation applies to induced voltage in the rotor bars.

Defect shown not to be due to loose rotor bars but more likely a result of mechanical/load related problem.

Polyphase motors have rotor bars shaped to give different speed-torque characteristics.

The rotating magnetic field induces a voltage in the rotor bars as it passes over them.

The current distribution within the rotor bars varies depending on the frequency of the induced current.

The major components of a rotor core are: rotor bars, resistance end rings and a shaft.

In induction motor rotors, the critical material is the electrical joint between the rotor bar conductors and the end rings.

These movements interrupt the circulation of stray currents through the magnetic core material (unless the rotor bars are insulated, which is not common).

The shape and depth of the rotor bars can be used to vary the speed-torque characteristics of the induction motor.

Rotor sparking may take place during starting and occurs between the rotor bars and rotor core.

The flux generates a magnetic field in the air gap between the stator and the rotor and induces a voltage which produces current through the rotor bars.

At standstill, the revolving magnetic field passes the rotor bars at a high rate, inducing line-frequency current into the rotor bars.

At standstill, the rotor current is the same frequency as the stator current, and tends to travel at the outermost parts of the cage rotor bars (by skin effect).

It is caused by movement of the rotor bars on starting, due to high forces at start-up, either within the slots or around the end of the core in the area where the bar is shaped.

Polymanager allows a non-specialist to verify the integrity of data of this type and carry out a full diagnosis of the current spectrum, using sophisticated graphical displays, rotor bar reports and exception reports.

Evaluation of the rotor velocity requires extra speed transducers and the value of the rotor time constant is directly affected by changes in the resistance of the rotor bars due to changes in temperature.

Users of HV motors should consider machine applications where torsional resonance of the complete motor/load drive train might occur, as this may increase the probability of sparking, e.g. because of higher forces on the rotor bars.

During this time the motor is under the mechanical influence of the rotating load and, at the instant of disconnection, current will still flow in the rotor bars due to the time delay necessary for the magnetic flux to die away.

By tapering the profile of the rotor bars to vary their resistance at different depths, or by constructing a double squirrel cage, the motor can be arranged to produce more or less torque at standstill and near its synchronous speed.

Motor energy loss is mainly heat caused by many factors, including loss from the coil winding (resistance), loss in the rotor bars and slip rings, loss due to magnetising of the iron core, and loss from friction of bearings.

The ignition tests described above are representative only of normal operation with starts from the stationary condition and are not adequate for motors intended for auto re-start (an out of phase re-start may result in higher forces on the rotor bars, and a longer start up phase which may cause additional heating).