Is the star-delta starter example model correct?

Question

Phil Churn 2019-10-28

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回答： Joel Van Sickel 2020-8-18

I have used the star-delta starter example model in Simscape electrical (ee_asm_starting) to model star-starting and delta-starting of the motor in the example model (set the star-delta transition to 1 and 0 respectively). However, when observing the line currents, the ratio between star and delta starting, which under the basic fundamental theory should be a ratio of 1 : sqrt(3), seems nearly 1 : 2 (115 Apk : 235A pk). If the model included saturation then this might be an explanation, but it seems not to be set.

So, is there some aspect of the motor model that is being affected by the two different applied voltages - and if so, please can someone explain the difference that is being observed.

Thanks!

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Answer 1

Joel Van Sickel 2020-8-18

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Hello Phil,

this is the equivalent of taking a wye load and changing it to a delta load, so line current is modified by a factor of 3, not sqrt(3). You can see this if you simulate a wye vs delta resistive load using the same resistance for both. This lines up with the motor simulation if you compare their steady state current draws. The current draw is a bit different when speeding up because torque/slip also comes into play for what the line current is.

Regards,

Joel