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Industrial Reduced Voltage Starters and Soft Starters

In many places where industrial motors are used to drive motion, industrial starters often work hand in hand with these motors. In particular, reduced voltage soft starters are the most popular and are often placed inside industrial starter mount enclosures to prevent unauthorised people from tampering with them. Soft starters are devices that enable a gradual start for motors by slowly increasing the voltage. Typically, they control torque and cut down the starting current. They are designed to enable smooth controlled starting and stopping by reducing the motor's torque. Having an understanding of the various methods of soft starting, applications and benefits of soft starters can help you make the best buying decision.

Methods of Operation

Wye/delta, auto-transformer and solid-state starters are the main methods by which reduced voltage soft starters are started. Wye/delta starters have three contactors which allow for initial starting of the motor through a wye connection afterwhich a timed transition to a ‘delta’ takes over to allow full motor speed. Auto-transformer starters provide power to the motor through adjustable tap settings, usually 50 per cent, 65 per cent and 80 per cent of line the voltage, resulting to a decrease in current by the same measure at the motor's terminals. Solid-state starters employ controlled firing of thyristors to slowly increase the motor's supply voltage. This also controls the current and supplies only sufficient torque that gets the motor rotating, afterwhich the speed can be increased depending on set starting profiles. Primary resistor and part windings are also some other methods used for soft starting.


As is the case with most mechanical machines, sudden acceleration puts a lot of stress on electric motors. When this happens, mechanical wear and tear and extra heat are the result. Over time, this wear and tear builds up and can result to motor failure and costly repairs. Soft-starters reduce mechanical stress by providing smooth controlled acceleration. Furthermore, electrical problems, such as overloading and overheating, are reduced as the motor is prevented from drawing excess current.


Textile industries, sugar plants, saw mills, power sectors and steel industries are some of the areas where reduced voltage starters have found their application. Generally, they are suited for industries where speed and torque control, gentle mechanical starts and reduction of high start-up current is critical.

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