Electrical – Why is it that the Δ-Δ transformer needs much higher input power than the Δ-Y transformer

electric-machinetransformer

I'm in a course where we wired up a single phase transformer as delta/delta and delta/wye and tested the current on the secondary side, Is. I noticed that we needed more than twice as much input power in the delta/delta configuration as we did in the delta/wye configuration to generate the same secondary current.

Delta/delta

Delta delta

Delta/ wye

Delta wye

Does anyone know why this is?

Cheers.

Best Answer

You are confusing power and voltage in your experimental setup.

Let's assume you use three single phase transformers with a 1:1 turns ratio to build your three phase solutions using 415 V 3 phase as the input.

Star-Star would give 415v on the secondary

Delta-Delta would give 415v on the secondary

Star -delta is a stepdown transformer with secondary output voltage of 415/sqrt(3) = 244 V

Delta-Star is a step up transformer with secondary output voltage of 415*sqrt(3) = 705 V

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