Fluid-filled Cables Overview

Fluid-filled cables have been used in the UK since the 1960s in National Grid, power lines at 275,000 volts and 400,000 volts and the strategic extra high-voltage distribution networks at 132,000 volts down to 33,000 volts. The fluid acts as an electrical insulator and is much less expensive than the next cheapest option. While the environmental risk associated with leakage from old cables is low with only a very small percentage ever  developing leaks, it remains a cause for concern.

There are 7,800 km of fluid filled cable in the UK which have proved extremely reliable electrically and in terms of leakage. ENA member companies recognise the potential environmental impact should fluid-filled cables fail. So jointly with the Environment Agency (EA), we have drawn up a voluntary code for managing fluid leaks. Companies regularly report all details of leaks to the EA and meet regularly to exchange best practice, new developments and learning points.

Modern cable fluid is biodegradable and poses minimal risk to the environment but even so, ENA member companies have not installed any new fluid filled cable routes for many years.

ENA members in the electricity sector regularly review the reliability of fluid filled cables as part of their capital investment programmes and take into account the potential environmental impact of leakage from fluid filled cables when considering their replacement. These cables are expensive major network assets forming a significant proportion of the strategic electricity networks.

ENA believes that the continued use of the fluid filled cables currently in operation presents a low risk to the environment if they are well managed and replaced at the right time. Any increase in the current rate of replacement would have to be justified given the huge costs involved and the small environmental benefit.