resistor design

[dow]

information on calculating resistor values and ratings for transition resistor used in star delta starter

 

[nbucska]

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Plesae read FAQ240-1032
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[jraef]

First, stop resting your little finger on the "Enter" key.

Second, there is no universal formula that I know of, but in general you are trying to avoid a transition spike in current, so you would want to have the current (through the resistors) to be the same as the motor current in Wye (Star) at the point of transition. Trial and error is one way, i.e. using a variable resistor bank and changing the slide position once you have it installed. If you know everything about your load torque requirements and motor torque curve you could calculate it. Take the load accelerating torque requirement curve, plot that against the torque output of your motor in Wye (Star), determine your transition time (i.e. when you stop accelerating and/or run up against the thermal damage curve of the motor), calculate current at that point (which means knowing your power factor at that point as well) and then finally calculate your resistor value to maintain that current during transition to Delta.

Third, give it up and buy a solid state soft starter and be done with the entire mess. It WILL cost you less and work much better. Just wire your motor in Delta to the soft starter.

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Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[powerjunx]

Try googling to SIEMENS, i have a catalog before which specifies resistor rating for motor applications, as in your case.