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Multiple Motors And Dual Speed Motors On Soft Starters


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I have an application where we are trying to determine if a soft starter could be used to ramp from low speed to high speed on a dual speed motor. The dual speed motor has six terminals with two star connected windings, one for low (8 pole) and one for high (2 pole) - not a dahlander type.


The setup would include a low speed contactor (on output of starter), high speed contactor (on output of starter), motor parameter (low/high) input, low and high start relays. The contactors and relays would be interlocked as to avoid being on at the same time.


Does anyone have experience with such an application or can point out any problems that might arrise from this configuration?


I can see that switching between the two speeds at stop shouldn't be a problem but switching to the high speed whilst the motor is already running... I'm not sure.







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Hi Leigh


I have done this many times without problems.


You can either DOL start at low speed and use the soft starter in high speed only, or you can use the soft starter in low speed and in high speed. (What I normally do.

There is no problem using a soft starter on a rotating motor except where you are using a special torque algorithm, so you use the soft starter in either a voltage ramp, or in a controlled current mode.

You must have a delay between opening the low speed contactor and closing the high speed to prevent the open transition type problems, and if you are using the soft starter in low speed and in high speed, you need to switch the parameter sets as the motor ratings are different for the two speeds.


Best regards,

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