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Technical comparison between RVSS and Auto Transformer for MV soft starter .

Kindly find the below document :

http://mt.schneider-electric.be/Main/Motorpact/catalogue/AMTED303042uk.pdf

in page 2 & 3 and i found that the main difference is in the deceleration option that is shown in the flow chart


this application guide (AMTED303042) is the best document to help selecting the good Motor starter type

However we need to clarify the below points :

1. The selection of the good Motor starter type is strongly dependent on the customer application, there is no need to penalize the customer with more investment (RVSS) while his application can be covered by RVAT

2. RVAT : Reduced Voltage Auto-Transformer motor starter is mainly used when the network cannot withstand high inrush current. An auto-transformer motor starter provides reduced voltage to the motor terminals during starting, with a three phase auto-transformer. It reduces the line current and provides the right starting torque.

3.RVSS: Reduced Voltage SoftStart motor starter is providing smooth, stepless acceleration and deceleration regardless of the load. This starting method lowers the starting current of the motor, reduces electrical stresses on the network and the motor. It reduces peak starting torque stresses on both the motor and mechanical load components, thereby providing longer service life and less downtime.

Accordingly it is preferable to follow the flow chart in the application guide to best answer the customer application
 
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