Soft start and stop of the electric motor. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors
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Semiconductor low voltage motor soft starters (SSRV) are used to reduce the destructive effect of sudden current surges that cause mechanical stress in equipment and system components. At ABB Inc. the main emphasis is on expanding the functions of "soft" starters, which can also be used as motor protective shutdown devices. The operation of such starters is based on the control of the motor current, voltage and temperature. A new approach to solving the problem is to smoothly increase the torque, not the voltage on the motor.
The soft starter calculates the real stator power, stator losses, etc. as a result, the real power transferred to the rotor. It is important that the torque of the motor is no longer directly dependent on the voltage applied to the motor or on its mechanical characteristics. The increase in torque occurs in accordance with the timed acceleration curve.
Eaton's low voltage soft starters (S752, SB01 and S811) use 24V pulse-width modulated (PWM) voltage to drive the contactor winding. The device consumes only 5W in steady state. Danfoss Citronic motor controls cover the range up to 20kW (depending on input voltage). The smallest MCI-3 soft starter module is only 22.5 mm wide. The MCI-15 module is designed to operate with a motor up to 7.5 kW at 480 V.
An important feature of SSRV starters is soft stop of the motor. ABB's PST Series soft starters include a plain text HMI interface for easy soft stop operation of centrifugal pumps, crushers, agitators, etc. The devices continuously monitor the motor torque to determine when the pumps will begin to slow down as soon as a stop command is given.
Sirius starters from Siemens offer three ways to stop the motor: coast to stop, soft stop, and injection into the DC windings. The new Sirius 3RW44 starter combines DC injection braking and closed loop torque control. This allows a quick stop of moving loads.
Information sources
- rtocman.ru
- siemens.com
Author: V.Novikov
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