The question I am working on:
"The power stations providing electricity for the National grid generate electricity at 400kV. The typical demand on an average winter's day is 6000MW. The current in the transmission lines is 15kA. Each pair of 400kV supergrid conductors has a resistance of 0.034Ω per km. How much power is lost per kilometer heating the conductors."
Upon looking at the answer, it was achieved using ; P=I^2R so that P=15kA^2 x 0.034 = 7650000
However I was using the other equation for power which is V^2/R and I ended up using 400kV^2/0.034 which gave the wrong answer. Why is the method I used wrong in this situation, and how do I know when to apply the correct power equation?