Soft Starters Explained
A Soft Starter is a device used with AC electrical motors to temporarily reduce the load and torque in the power-train and electric current surge of the motor during start-up. This reduces the mechanical stress on the motor and shaft, as well as the electrodynamic stresses on the attached power cables and electrical distribution network, extending the lifespan of the system. Electrical Soft Starters can be any control system that reduces the torque by temporarily reducing the voltage or current input, or a device that temporarily alters how the motor is connected in the electric circuit.
Starting of induction motors is accompanied by inrush currents up to 7-10 times higher than running current and starting torque up to 3 times higher than running torque. The increased torque results in sudden mechanical stress on the machine which leads to a reduced service life. Moreover, the high inrush current stresses the power supply, which may lead to voltage dips. As a result, lifespan of sensitive equipment may be reduced.
A Soft Starter eliminates the undesired side effects. Torque surges entail high mechanical stress on the machine, which results in higher service costs and increased wear. High currents and current peaks lead to high fixed costs charged by the power supply companies (peak current calculation) and to increased mains and generator loads.
A Soft Starter continuously controls the three-phase motor’s voltage supply during the start-up phase. This way, the motor is adjusted to the machine’s load behaviour. Mechanical operating equipment is accelerated smoothly. This lengthens service life, improves operating behaviour, and smooths workflows.
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