Power in High Voltage Lines:
Lost in Transmission

Electrical power transmission losses are natural and cannot be totally avoided. However, the extent of these transmission losses can be managed to a minimum by using high-quality conductors, reducing conductor resistance and maintaining a good balance between voltage and current.
But in fact, losses in medium- and high-voltage transmission lines worldwide are on the rise. Today's transmission line network runs at or near maximum capacity for long periods of time, often years. The high demand places substantial stress on the lines, which leads to significant wear and tear. As a result, the average age of transmission line infrastructure has increased, while interest in new development has fallen.

Tower For High Voltage Transmission Line
Tower For High Voltage Transmission Line (credit Pexels)

What causes transmission losses?

Transmission losses result from the fact that electrical energy cannot be transmitted through a transmission line without some loss. There are three main causes of transmission losses:

  • Conductor Resistance
    The current flow through the conductor is accompanied by the generation of heat due to the resistance of the conductor material. This heat is lost as energy and cannot be used to power any loads connected to the line.
  • Transformer Losses
    Electrical energy is also lost due to the inductance of transformers and other current-carrying equipment connected to the line. This current is transformed into a magnetic field and then back into a current again. This has the same effect as resistance in that it causes the generation of heat that is lost.
  • Reactance
    When electrical energy is being transmitted through a transmission line, the current and voltage waves may not coincide with each other. When this happens, the voltage and current are out of phase and the transmission line itself is working against capacitive- or inductive resistance.

Which losses are considered to be normal?

At normal transmission lines, 10 % to 20 % of the total power transmitted is lost due to resistance in the line itself, the transformers and eductors. Typically, there are long time loss statistics for transmission. For example, in Europe, losses in medium- and high-voltage transmission lines have been increasing at a rate of about 0.5 % per year since 2010. This increase is primarily due to the growing share of renewables in the energy mix, which leads to higher line currents and, consequently, larger losses.

Monitoring the losses and comparison with historical values is essential for decision-making. At the same time, a regular verification of the metering installations is important. This includes not just the accuracy of the energy meter, but also the entire measurement circuit, including instrument transformers and burdens.
Regular means, based on German praxis, every 3 months for high-voltage measurement systems and every 6 months for medium voltage.


Transmission line networks today operate at or near full capacity for extended periods of time, typically years. In many cases, it's necessary to extend the transmission capacity. Because transmission companies are mainly private, investments like additional transmission lines are often delayed.

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Thank you for reading and stay safe!

Editor's note: This article was originally published in September 2022 and has been updated for comprehensiveness.

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