My team and I are having a very hard time understanding how to solve for calculating power loss along a line. I think the terms / equations are similar to Ohms Law but not quite the same and that is mixing us up. Here is an example question for an older test:

A power plant in Chicago is generating 900 MW on 700 KV. Assuming the line is 100 kilometers long, with a resistance along the line of 0.2 ohms

A. What is the current flowing along the line?

Using Ohms Law, current is I=P/V 900 MW / 700 KV = 1286 amps

B. How much power is lost in the lines?

This is where we get confused. The answer key says find the voltage drop = current (amps) * resistance (ohms) 1286 * 0.2 = 257.2 kV. Then find power lost = amps * kV 1286 amps * 257.2 kV = 330.76 MW

We don't understand these equations and how does the line distance factor in?

C. What is the percentage of the power lost?

This should be easy taking the answer to B / 900 MW.

Can someone please help explain how to solve these kinds of problems or point us to resources to learn from? Thank you for the help.

For part B, you are not looking at the units. You should do 1286 * 0.2 = 257.2 kV (like you did). But then, 1286 amps * 257.2 kV = 330,759 kW. The reason that the correct answer is in MW, is because the values that started the problem were given in MW. To convert your answer, know that 1 MW is 1000 kW. So it is 330.76 MW.

For part C, you are correct, it is 330.76MW / 900MW = 36.75%.

I once had a teacher that took off points if we did not carry the units throughout the problem. We could only cross off the unit if they matched. This habit stuck with me, and it has really helped me, so try that.

I hope this helps