In general, soft starters are not used to save energy, but often save money in the form of reduced maintenance costs. Y-Delta starters are very hard on the mechanical systems of your motor and driven load because when they transition from Start to Run, there is a spike of torque that occurs, sometimes even higher than if you had started across the line (DOL)! Soft starters will reduce or eliminate that damage from torque spikes.
But as to energy savings, not in 99.99999% of applications. If the soft starter has the "Nola Energy Saver" circuit in it as discussed in the FAQ, there is a very slight possibility of a minor amount of savings
IF the motor is unloaded for long periods of time, but not if the motor is being used within its normal operating range. As Marke says in the FAQ, you can only save energy that is being wasted. If your motor is already running efficiently, you are not going to be able to save much more than that.
If the motor is unloaded for long periods of time however,
there is no better energy saver than the Off switch. A side benefit of a soft starter then is that it becomes less of a problem to turn motors off when not needed because there will be less electrical and mechanical shock when re-starting them.
JRaef.com
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