Crossrail is a new 118km railway line under construction, running from Maidenhead, West of London, to Abbey Wood, East of the capital. The track will pass through 21km of twin bore tunnels, running directly under the centre of London.
As the tunnels run through the centre of the city, they pass underneath many landmark buildings and important infrastructure; including two large substations that are critical to the capital’s power distribution network. The works introduce the possibility of subsidence and ground movement that could possibly disturb the switchboards.
Partial discharge tests carried out in Oct 2012 showed that the switchboards were free from PD. A permanent PD monitoring system has been installed in each substation, in order to both continuously check the switchgear for PD and to raise alarms if any PD is initiated as a result of the underground works.
The Crossrail tunnel is scheduled to pass under the two substations, Dukes St and Short’s Gardens, between January and March 2013.
Maps showing tunnel route and substation locations
Duke St substation is an underground substation built in 1905, containing 11kV switchgear dating back from the late 1980s. Short’s Gardens has both 11kV and 22kV switchgear dating back to 1953.
Previous evidence has indicated that the tunnelling works may introduce ground movement of up to 14mm. This change in ground level could take place over a prolonged period of time; therefore any consequential effects on the health of the switchgear could occur a long time after the tunnelling has taken place.
A permanent PD monitoring system has been installed as to benchmark the condition of the switchgear prior to the works, and to continuously monitor for the onset of PD as the works progress.
The monitors have been installed with both capacitive TEV PD sensors and ultrasonic acoustic PD sensors, so that any degradation to both insulation surfaces and internal insulation will be
detected and raise alarms.