Difference Between Soft Starter and Star-Delta Starter

What is a Soft starter?

The soft starter is a semiconductor-based motor starter that regulates the voltage supply to the motor with a thyristor. To minimize the inrush current that can harm the motor windings, the voltage is decreased at startup. When the motor reaches its rated speed, the voltage is progressively increased.

What is a star-delta starter?

A star-delta starter is the most commonly used method for the starting of a 3 phase induction motor. When the motor reaches about 80% of its full load speed, it will begin to run in a delta-connected stator winding. 

Difference between soft starter and star-delta starter:

  • Star delta starter only has two states, low voltage, and full voltage, that the starter jumps between, soft starter start-up gradually, they can have infinite states within the limits of the controlling electronics and your startup requirement.
  • The soft starter can handle varying load conditions, such as loaded and unloaded starts, while the star delta starter can not.
  • Soft starter allows you to control the starting time, while star-delta starters do not. The starting time for the star delta starter is about three to seven seconds, while the soft starter has an adjustable time of between one and around 60 seconds. 
  • Some soft starter also offers soft stop functionality, while the star delta starter does not.
  • Star delta starters are more complicated than a soft starter. It is also easier to install a soft starter.
  • With an extremely light load, Star delta able to reduce the starting current to a lower level than a soft starter could. 
  • Soft starters offer dynamic torque control, which allows you to adjust the torque to accommodate different motor and load characteristics with star delta starter, you can't adjust the starting torque. 
  • Star delta starter, between the star and delta connection, there is an open transition that can result in transients and high torque. During this transition, there is also a power outage. With a soft starter, there is no such open transition and no power loss. 
  • Soft starter cost more than a star-delta starter, although soft starters is more efficient. However, the cost difference between the two types of starter is less than what it once was.
  • Star delta starter can be used for low power machines starting load, medium power machines without load, low power fans, and low power centrifugal pumps, The soft starter, on the other hand, may be used with large motors with or without load, such as those used in compressors, fans, pumps, conveyors, agitators, mixers, mills, and other applications.

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