Dual Voltage Motors & Star-Delta Starting

A. Star Delta Starting: Star-Delta starting is frequently referred to as “Soft-starting” a motor. But what is soft about this starting method? Why is it used? What are the advantages? What are the disadvantages? Let’s first analyse what Star Delta starting is! It will be explained by using an example motor. What is Star Delta starting? Star Delta starting is when the motor is connected (normally externally from the motor) in STAR during the starting sequence. When the motor has accelerated to close to the normal running speed, the motor is connected in DELTA. Pictures will show the two connections for a series connected, three phase motor. The change of the external connection of the motor from Star to Delta is normally achieved by what is commonly referred to a soft starter or a Star Delta starter. This starter is simply a number of contactors (switches) that connect the different leads together to form the required connection, i.e. Star or Delta. These starters are normally set to a specific starting sequence, mostly using a time setting to switch between Star and Delta. There can be extensive protection on these starters, monitoring the starting time, current, Voltage, motor speed etc. The cost of the soft starter will depend on the number of starts required per hour, run-up time, Voltage, power rating, and protection devices required.The most significant advantage of using Star-Delta starting is the huge reduction in the starting current of the motor, which will result in a significant cost saving on cables, transformers and switch gear.If the load torque is equal to the motor’s torque, no acceleration will occur The dual Voltage is purely for versatility sake, and NOT to reduce starting currents
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