Engineering Voltages, currents and power between a power plant and a transformer

[stipan_relix]

Homework Statement

Calculate voltages on the main plant switchboard, M1 and O, power and current loads, etc.

Relevant Equations

I=P/sqrt(3)*U*cos(phi), Z=X*l - but I don't think this can be used here and I don't have an idea of any other equations to use

This is the first part of the problem, which I solved.

Now to the second part which I can't manage to find the equations I need to use.

Problem:
This plant is connected to a 20/0.4 kV transformer of 250 kVA power, through an XP00-A cable (4x150 mm², I_N=300 A, Z₁=0.26 Ω/km).

a) Calculate voltages for the main plant switchboard and voltages on the connections to M1 and O
b) Are those voltages within the 10% tolerance?
c) Do the cables meet the real current load requirements?
d) Does the transformer meet the real power load requirement?

Cables:
Plant to transformer: 4x150 mm², I_N=300 A, Z₁=0.26 Ω/km
Installation cables (M1 and O): 4x50 mm², I_N=150 A, Z₂=0.705 Ω/km
_________________________________________________________________________________________________________
This is everything I tried to do, and I don't know if any of it is right.

Do I just need to use the values I got in the first part, or what? I know of the Z=X*l equation, but I have no given length here, so I have no idea what else to use for any of this, including voltages for the switchboard and for M1 and O.

 

[Babadag]

 

[stipan_relix]

View attachment 257399

So do you think this is unsolvable without cable lengths?

 

[Babadag]

The cable length is required in order to calculate the cable actual impedance.

If the 20 kV line voltage will be the unchanged voltage then the transformer impedance also will be required in order to calculate the voltage drop.

If the Main Switchgear has to be able to get the rated transformer current the XPOO-A cable is too small.

 

[stipan_relix]

The cable length is required in order to calculate the cable actual impedance.

You were right, just got an email from the professor that he forgot to include the cable lengths. Thanks for trying to help!