Three Phase Wye Delta Transformer Feeding Single Phase Load

[BuzzBar]

Three wye-delta (120:480) is feeding single phase load as per diagram. How will current be distributed in the delta winding when single phase is connected between line A and B ?

When I solve by hand I get different results when simulating in Multisim.
Hand calculation - Winding A will be in parallel with winding B&C (which are in series and B+C=-A). This will cause the current to be split evenly between windings A (50A) and B&C (50A).

However when I use Multisim currents are winding A (66A) and B&C(33A).
Which calculation is correct? I don't understand how Multsim is solving winding A to carry double the current in winding B&C,

 

[berkeman]

Welcome to PF.

Is this for schoolwork? If so, I can move it to the schoolwork forums for you. Also, can you clarify on your diagram which are "line" A/B/C and "winding" A/B/C? Thanks.

 

[DaveE]

I haven't actually tried to solve this yet, IDK, maybe later. But I suspect that you might be adding up the currents algebraically, without regard to their phase difference. In fact, they will add like vectors with 120^o angles. The problem is well defined with that "phasor" provision. Frankly, it's just a book keeping exercise of KVL/KCL with out of phase sinusoids.

Please let us know what confuses you about the analysis by hand. Write out the equations of the voltages and currents in the secondary circuit (I know, it is a PITA, that's why I haven't done it for you, yet, LOL). Sorry if I'm not giving you credit for knowing about vectors/phasors in circuits. Often there is a bit of guessing required about the OP's background knowledge.

 

[BuzzBar]

Welcome to PF.

Is this for schoolwork? If so, I can move it to the schoolwork forums for you. Also, can you clarify on your diagram which are "line" A/B/C and "winding" A/B/C? Thanks.

Hi, yes its is for school. I added line and winding currents designation to the diagram.

 

[BuzzBar]

I haven't actually tried to solve this yet, IDK, maybe later. But I suspect that you might be adding up the currents algebraically, without regard to their phase difference. In fact, they will add like vectors with 120^o angles. The problem is well defined with that "phasor" provision. Frankly, it's just a book keeping exercise of KVL/KCL with out of phase sinusoids.

Please let us know what confuses you about the analysis by hand. Write out the equations of the voltages and currents in the secondary circuit (I know, it is a PITA, that's why I haven't done it for you, yet, LOL). Sorry if I'm not giving you credit for knowing about vectors/phasors in circuits. Often there is a bit of guessing required about the OP's background knowledge.

Hi, I rearranged the delta circuit and treat each winding as as voltage source. I use VAB for reference and consider it to be at angle 0. When I add VBC and VCA as vector sum I get them to be equal to -VAB. So from this I have two equal voltage sources, so current should be dived equally between two voltage source branches,

 

[Baluncore]

The circuit is overdefined by having three voltage sources, with a closed delta that must sum to zero. Something must give.

The voltage of the delta secondary, relative to ground is floating, unspecified.

 

[Averagesupernova]

You have two voltage sources across a single load. One has double the source impedance of the other unless otherwise defined. It should be clear after stating that assumption.

 

[Gavran]

It is obvious that Multisim has used the equation $I_{AC}+I_{CB}+ I_{BA} = 0A$ instead of $I_{BA} = \frac{I_{A}}{2}$ has been used by @BuzzBar.
The system is unbalanced and in my opinion the Multisim approach is wrong.