Liquid Rotor Resistance

These are used for controlling the starting of large slip ring motors.

In the wound rotor motor a instead of a series of rotor bars, a set of insulated rotor coils is used to accept external impedances. The rotor windings are similar to those found on a DC armature, with the coils connected together to a set of rings that make contact with brushes. The circuit is completed by connecting the brushes to a set of impedances such as a resistor bank or liquid rheostat. This construction design allows for a varying resistance from almost short-circuit condition to an open-circuit condition with infinite external resistance. By modifying the resistance, the speed-torque characteristics can be altered.

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www.oipenengineering.co.uk/liquidstarters.html