3 winding trafos

[melec]

Can anyone help me?

3 winding trafo: Primary: 600 MVA, 11kV
Secondary: 600 MVA, 400kV
Tertiary: 100 MVA, 11kV

There's a balanced load of 400 MVA @ .8 lagging p.f. on the secondary, which is maintained at 400kV line voltage, and a balanced load of 50 MVA at unit p.f. on the tertiary winding.

From short circuit test results, Per unit series equivalent reactances were calculated for inclusion in a single line equivalent circuit, using a 600 MVA, giving xp = j0.11, xs = -0.01j and xt= 0.85j.

I've been able to calculate the current taken by the secondary load but i'm stuck when it comes to the tertiary.

Can anyone tell me how to calculate load impedance connected to the tertiary? So that I can calculate the line voltages at the primary and tertiary windings?

Apologies if this is a silly question...

Thank you!

 

[magoo2]

Not a silly question.

You have a T network with your 3 equivalent impedances.

o-----Xp-----0-----Xs-------0
|
|
Xt
|
|
0

I'm sure you probably calculated the secondary current and voltage based on Xp-s and Vs. If you do it with the 3 impedances, you'll get Is and It flowing through Xp. This will have an effect on both the secondary and tertiary voltage.

See if that helps.

 

[melec]

Thanks Magoo2.

However to calcualate rsistive load connected to the tertiary, could I assume that the load is 50MVA at 11kV?

 

[melec]

Sorry for the incorrect spelling.

However to calculate the resistive load connected to the tertiary, could I assume that the load is 50MVA at 11kV?

 

[magoo2]

If you work with the 3-terminal equivalent, then you'll have 50 MVA on the tertiary, 400 MVA on the secondary and 450 MVA through the primary. As a first cut, you can use the nominal voltages to solve for the currents.

Is this a homework problem?

 

[melec]

Thanks Magoo2.

It's past a examination question for a taught Masters.