Three-phase transformer DC-resistances

[arnold28]

Homework Statement

Three-phase transformer, 20/0.5 kV, dyn11. Not connected to the grid.
DC-resistance between two primary windings is measured to be 80 ohm. What is the DC-resistance of ONE primary coil

Homework Equations

The Attempt at a Solution

I thought I could just calculate Ra there, because I assume all the coils are identical?
Is the 20/0.5 kV info even needed here?

 

[SirAskalot]

I assume the problem should be?

DC-resistance between two primary terminals is measured to be 80 ohm

Forget about d-y transformation.

Concentrate on the left figure, and deduce a formula for the total resistance seen from terminals A and B. And this formula equals (?). All winding resistences are equal.

 

[arnold28]

isnt the total resistance of the triangle that 80 ohms? so resistance of one winding should then be 80/3? well apparently not because i don't get the right answer with that

 

[SirAskalot]

As you said yourself, its not 80/3.

If all resistances had been connected in series, it would have been. But its not.

What is the formula for the total resistance seen from terminals A and B? Hint: One series connection and one parallell connection.

Draw a new figure if you don't see it.

 

[arnold28]

aaah stupid me, that's right, the triangle confused me :D
I calculated (80*80 / 80+80) + 80 and got the right answer!

thanks very very much