# Open-delta connection transformers

Discussion in 'Homework Help' started by nyasha, Feb 5, 2012.

1. ### nyasha Thread Starter Active Member

Mar 23, 2009
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So l have attached the question and my attempt to the solution. I think l answered all questions correctly....but for part c l do not know if l draw the phase angles of the winding currents and voltages with a 30 degrees phase shift between them ?

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2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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I would think the secondary windings are capable of carrying the full 543.5A at 460V line-line.

So the total load power would be √3*460*543.5=433kW.

Each transformer must carry half that power or 216.5kW.

The primary kVA per transformer with rated winding current & voltage is still 250kVA so each transformer is running with a power factor of 216.5kVA/250kVA=0.866

BUT ... the total 3-phase source power factor will be unity.

Last edited: Feb 6, 2012
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3. ### nyasha Thread Starter Active Member

Mar 23, 2009
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But wouldn't that damage the windings of the transformer ? Do we want that much current flowing into the windings of the transformer ?

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
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No since that value is the rated current for the secondary winding of each of the 250kVA transformers. One can draw the rated current without any damage.

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5. ### nyasha Thread Starter Active Member

Mar 23, 2009
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I am confused there. I thought the 250kVA was for three delta transformers connected. Which means when another phase is removed the power output decreases.

6. ### t_n_k AAC Fanatic!

Mar 6, 2009
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It's spelled out in the wording of the question which you might review ...

So two single phase transformers, individually rated at 250kVA are connected in open delta.