Life lines [power transmission system maintenance]

The transmission system in England and Wales has more than 7000 route-km of overhead lines, typically operating at 275 kV and 400 kV. It sounds impressive, but the number of lattice steel towers totals 22,000. Now owned and operated by National Grid, the bulk of the 275 kV network was built in the early to mid 1960s, while the 400 kV network was established in the late 1960s and early 1970s. To tackle the problem of ageing assets, National Grid embarked on a replacement programme in the mid to late 1980s. As the bulk of overhead lines reach their anticipated technical asset lives, the rate of replacement is increasing. Condition assessment and diagnostic techniques are therefore increasingly important to support the timely identification and replacement of assets before failure occurs.