ABB’s new Network Management system for the control of London Underground’s power supply has just gone live
In 1998, London Underground signed a 30-year, £1 billion Private Finance Initiative (PFI) contract with SEEBOARD Powerlink a consortium formed by EDF Energy, Balfour Beatty and ABB to manage, maintain, develop and finance London Underground’s high-voltage power supply system. One of ABB’s main roles in the first five years of the contract has been the design, installation and commissioning of a new single, centralised SCADA (Supervisory Control and Data Acquisition) SPIDER system for the power distribution network.
The London Underground (LU) power distribution network has a 22kV sub-transmission system with load delivered via an 11kV system to 158 delivery points. Local transformer rectifiers provide 630V DC (750V DC in future) for the train motive power as well as lower voltage supplies for lighting, lifts, escalators, ticket barriers, communications and control systems and so on. ABB’s task was to implement a new fully integrated SCADA system to provide overall control of the network, in place of the five existing SCADA systems. This was a considerable challenge for a network serving some 250 miles of track and 270 stations, each with its own substation, and an annual power requirement of some 900,000MWhr. Especially as disruption to passenger services had to be kept to an absolute minimum.
At the design stage, the SPIDER system received intensive input from ABB, SPL and LU to customise it to an underground working environment. In particular, there were specific safety and dual operator considerations which had to satisfy HMRI (Her Majesty’s Rail Inspectorate).
Access for work was restricted to a short window in the small hours of the morning when the whole LU network shuts down for cleaning and maintenance requiring careful planning to ensure restoration.
The SPIDER SCADA system has been fully integrated with LU’s existing communications system. Control of the network is now centralised in two replicated command centres (main and emergency) manned both by LU staff, who are responsible for DC traction feed, and SPL staff, responsible for AC supply. Great care has been taking in the ergonomic design of the command centres to provide optimum conditions for the operators. Control can be switched between the centres to ensure safe and reliable operation in an emergency.
Commissioning of the SPIDER system, which was completed in the early Summer of 2004, was progressive to ensuring no interruptions to supply as control was switched over from the five existing SCADA systems in a phased approach. The design allows for expansion to meet some of the expected future system changes and migration over the 30-year lifetime of the PFI project.
A key element in the PFI scheme was the planned closure of LU’s dedicated 180 MW Lots Road power station, with LU taking all its power from the National Grid, via London’s local Distribution Network Operator, EDF Energy.
Discussions with EDF Energy identified that the additional traction load on the local distribution network, due to the diode rectifiers which feed DC electricity to the trains, would have an adverse effect on the power quality for the London area unless corrective action was taken.
A £60 million ‘Power Quality’ variation to the original PFI contract was agreed and ABB was asked to carry out a series of extensive studies of the existing electrical system. These studies checked the potential for harmonic distortion and voltage fluctuation under all credible, different, power supply network variations likely to be encountered. It then went on to ascertain the nature and size of the power quality correction installations needed to smooth load fluctuations and reduce harmonic disturbance.
Following the studies, ABB went on to install a total of five Static Var Compensators (SVCs) and ten stand-alone Harmonic Filters in critical points of the LU 22kV distribution grid.