Crane gets a lift from slipring motors

Paul Boughton

A slipring motor is a wound rotor induction machine in which the coils of the rotor are terminated in slip rings to which external impedances can be connected. The stator is similar to that of a standard squirrel cage motor. Varying the impedance in the rotor alters the speed/current and speed/torque curves of the motor.

Slipring motors provide high torque at start up and throughout their full speed range by varying the resistance in the slipring starter. This technique can also be used to provide variable speed. They are compact, lightweight, low maintenance and long life, making them suitable for crane duties within the mining industries.

The Marathon KS series of slip ring motors, from Regal, is rated for crane duties and based on a cast iron/fabricated body, integral feet design.

The Marathon KS series has been design optimised for best performance in crane applications. For instance, its feet are extra thick to ensure that mounting is safe and secure for long term use. Also contributing to its long-term reliability, it has a separate compartment for the slip rings which is generously dimensioned for easy access. It is rated as IPW55 protected and has high performance ventilation to make it tolerant to less than suitable environmental conditions. It is also provided with thermistor protection.

The stator frame is of fabricated steel construction, while the insulations options are Class F/F as standard and Class H for use in demanding applications. While thyristor control is also provided as standard, the KS series is also suitable for electronic control and is available in Frame sizes from KS112M to 560 LX and provide outputs from 2kW, 6-pole to 860kW, 10-pole.

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