# Energy efficiency, Transformer?

1. Oct 31, 2014

### Daisy

1. The problem statement, all variables and given/known data

A power plant produces energy at a voltage of Vi = 12693 V. Before being sent along long distance power lines this electricity is sent through a transformer with 166 turns in the primary coil and 6917 turns in the secondary coil. The voltage of the electricity sent through the long distance wires is 528900V.
If the wires have an efficiency of 99.30% and a resistance of 1089 Ω, what current flows through these wires?

2. Relevant equations

I have used V=IR. Of which I got V to be 485.67 and I mil

3. The attempt at a solution

I got I = V/R to be 485.67 and I multiplied it by 0.993 in order to determine the current flowing through these wires. But I got it wrong. I don't seem to understand what is wrong. Did I use the correct equation? Or was my computation of efficiency incorrect?

2. Oct 31, 2014

### Staff: Mentor

R is the resistance of the transmission wires and doesn't include any load resistance at the receiving end. That means your current calculation is not correct.

Instead, start by writing an expression for the voltage received at the far end assuming some (as yet unknown) current $I$ is flowing.

Next consider the definition of Efficiency in this context (power transmission).

3. Oct 31, 2014

### Daisy

I am really confused. What do you mean by voltage received at the far end?

4. Oct 31, 2014

### Staff: Mentor

Power station at one end of the transmission line, some load at the far end. The transmission line has resistance so there will be a voltage drop between the sending end and the receiving end. Thus the voltage received at the far end is not the same as the voltage at the sending end.

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