Network Rail Southern territory is the UK's largest private operator of electrical distribution. It takes power from feeder points on the grid at 66kV, 33kV or 11kV and distributes them around the network. Before the PSU project there were 27 grid feeder supply points. The project will add a further three.
Network Rail takes the AC power from the grid and runs it along trackside power cables to rectifying sub-stations.
These convert it into the 750V DC that feeds to the third rail that powers all trains in the region (Eurostar excepted).
Track paralleling huts between the sub-stations contain switch gear to allow connection or disconnection different electrical sections of track.
Before the PSU project substations were unable to cope with the extra power demand and the switch gear was too far apart, Mitchell says. The PSU has involved work on 90 substations (upgrading some existing and building some from scratch) and tapping them into the track to put in more power; laying 300km of extra cable and creating 78 new feeder routes to distribute more power to the sub-stations. Software in the seven electrical control rooms is being modified to suit the new set up.