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Technical Losses

Transferring electricity is not like transferring water or gas, and network losses are not like a water leak or a gas leak. They are a characteristic part of the electricity distribution network and we know that there will always be some power ‘lost’ to the system.

Technical losses are the losses that occur within the distribution network due to the cables, overhead lines, transformers and other substation equipment that we use to transfer electricity. 

There are two types of technical losses, fixed and variable:

  • Fixed losses are constant  and can only be reduced by replacing older assets with modern high efficiency equipment.
  • Variable losses change as the amount of power flowing changes; in a highly loaded network they are much greater than fixed losses.



Variable losses are due to a current passing through the electrical resistance of network assets.

Some energy is lost as waste heat as the current causes the transformer, line or cable to heat up.

Variable losses have a non-linear (squared) relationship with the current passing through the asset.

Therefore variable losses are highly dependant on the power flows through the network which are driven by customer behaviour.

Fixed losses are virtually constant as long as the asset is energised. This mainly affects transformers where energy is lost as heat and noise due to the magnetic forces in the transformer core.

At very high voltages, overhead lines incur fixed losses in the form of corona discharge. At voltages used in our distribution networks these losses are negligible.

Cables incur fixed losses due to the charging current required to energise the cable. These effects are small unless the cable is very long, or operates at very high voltages.

Although we can improve our understanding of these losses and where they arise, we can never fully remove them. They are an unavoidable by-product of electrical conduction.



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