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Simulating Soft Starter


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#1 keerth

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Posted 09 February 2011 - 07:50 AM

Hi,

I would like to know how should I decide on the ramp time and the amount of voltage applied (open-loop soft starter)
to simulate a simple soft starter using Matlab?

The motor I am using is a 150HP squirrel cage motor.

Thank you

cheers,
Keerth

#2 marke

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Posted 09 February 2011 - 06:00 PM

It depends on the type of soft starter and the starting algorithm used.
first, the initial start voltage must provide enough torque to overcome the load torque at zero speed by a margin to give you an acceleration torque.
Second the voltage profile must enable the voltage to vary at a rate that ensures that there is sufficient torque to accelerate the motor to full speed allowing for changes in load torque as the speed increases.
If you use a simple timed Voltage Ramp algorithm, then you need to ensure that the rate of rise of voltage is appropriate for the inertia of the load. If you have a short ramp with a high inertia load, you will be at full voltage before the motor reaches full speed and have a very high current. If you have a long ramp with a low inertia load, you will have a motor at full speed with low voltage and resultant high slip.

Best regards,
Mark.




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