Why Does Using High Voltages in Power Transmission Reduce Losses?

[paul_harris77]

We are constantly told at school that in order to reduce power loss in overhead cables, high voltages and low currents are used as P = I squared R. This seems to make sense until you substitute I=V/R into P=VI and get P = V squared / R. Now if voltage is increased in the cable, and resistance is decreased, power loss is at its greatest, completely opposite to the other example. Am I doing something wrong?

Many thanks

Paul Harris

 

[skeptic2]

We are constantly told at school that in order to reduce power loss in overhead cables, high voltages and low currents are used as P = I squared R. This seems to make sense until you substitute I=V/R into P=VI and get P = V squared / R. Now if voltage is increased in the cable, and resistance is decreased, power loss is at its greatest, completely opposite to the other example. Am I doing something wrong?

Many thanks

Paul Harris

What you're saying would be true if the high power line were shorted to ground and all the voltage were across the line. In practice the line feeds a transformer with an impedance much higher than the line. So in reality most of the voltage is across the transformer and the voltage across the line is very low.

 

[thomate1]

Hello Paul,

Thank you for your question. You are correct in your understanding of the relationship between power, current, and resistance. However, there are a few key factors that need to be considered when discussing high power transmission.

First, it is important to note that the formula P = I^2R assumes a constant resistance, which is not always the case in real-life situations. In overhead cables, the resistance can vary due to factors such as temperature changes, corrosion, and other external influences. In these cases, using high voltages and low currents can still help to reduce power loss.

Additionally, high power transmission also takes into account the efficiency of the transmission system. Higher voltages allow for the use of smaller and more efficient conductors, which can help to reduce power loss. This is because smaller conductors have lower resistance and therefore less power is lost as heat.

Furthermore, high power transmission also involves careful design and engineering of the entire transmission system, including transformers, converters, and other components. These components are designed to work together to minimize power loss and ensure efficient transmission.

In summary, while it may seem counterintuitive, high voltages and low currents are still the preferred method for reducing power loss in high power transmission systems. It is important to consider all factors and components involved in the system and not just focus on one aspect in isolation.

I hope this helps to clarify your understanding. Keep asking questions and exploring the world of science!