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Soft-start eases slip-ring motor stresses

22 April, 2010

At the recent Hannover Fair, ABB unveiled an electronic soft-start system for slip-ring motors used in heavy-duty applications such as conveyors, mixers and crushers. These applications often need a starting torque close to or even above the nominal torque of the motor, and place heavy demands on gears and couplings, resulting in significant wear and tear, and high maintenance costs.

The Ecoss electronic starter (shown above) is designed to provide a controlled, continuously variable start-up which puts less stress on the motor and mechanical components. It works by rectifying and then modulating the rotor current. At the core of the system is a power electronic module incorporating a rectifier, IGBT switch, snubber module, and actuators. This module receives a PWM (pulse-width modulated) switching cycle from a control module which carries out both open- and closed-loop control of the starting process, as well as monitoring and controlling the blower and short-circuit contactor.

The starter can provide simple start-ups by reducing resistance constantly with variable start-up times and maximum torque levels. It can also deliver constant-torque control or speed-controlled start-ups. It can handle rotor starting currents of 800A with a maximum standstill voltage of 1.7kV, making it suitable for motors rated up to about 1.5MW.

The starter can be integrated with control networks via Profibus, and with ABB’s Drive Window diagnostic and parameterisation system.

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