The demand for train services in London is large, growing, and is expected to continue to do so despite the hiatus caused by Covid-19. This trend has been apparent since the early 1980s. London Underground (LU) has been running more and more services for over 30 years and has been upgrading its lines’ capability as trains and signalling become due for renewal. The Central line (see Panel) was the first such integrated upgrade with the 1992 tube stock trains introduced from 1993 and ATO in 2000/2001.
The trains are now nearly 30 years old and are doing far more work than was ever planned, some 160,000 km per train, per year compared with the designed 127,000 km. This article will describe how London Underground is dealing with train reliability and obsolescence issues for the next 10 years or so.
Background
During the early 1980’s LU started to introduce electronics on its trains and there was also great interest in further reducing train weight. 1973 tube stock (Piccadilly line), D stock (District line), and 1983 tube stock (Jubilee line) were fitted with electronic equipment monitoring systems, and LU had pioneered the use of aluminium in the construction of its trains. Tube trains had retained the steel underframe, but LU wanted to take advantage of the strength and light weight of monocoque aluminium structures using large aluminium extrusions. In addition, GTO thyristor ‘chopper’ control and electronic control systems were becoming readily available.
Chopper control allowed much higher performance in the open sections of the line whilst enabling lower speed in tunnels without the waste of energy that would have been involved if resistance controllers had been retained, as there were no resistors needed in the motor circuits for lower tunnel speeds. This and ATO delivered a much-improved service frequency with reduced journey times. 85 trains were required, only about five more than the old fleet size. All these concepts were tried out on the 1986 tube stock prototypes prior to the 1992 tube stock being ordered from British Rail Engineering Ltd in 1989. 1992 tube stock is made up of four, two-car units with all axles motored. They have a lot of electronics and are the lightest passenger cars on the LU network.
Most of the electronic components specified were new and had never been fitted to trains before. They included components that could reasonably be expected to be obsolete long before the end of the nominal 40-year life of the mechanical parts. No one knew what the life of the electronics might be, but the best advice was ‘about 20 years’.
In service, the 1992 tube stock has been more troublesome than had been hoped and has required significant unexpected expenditure to keep it going, including the replacement of the bogie frames due to premature cracking. The traction motors themselves have a very hard life with frequent motoring and braking and need a lot of maintenance – much more than forecast. Given that there are 32 motors on every train, this has been a significant burden. There have also been some body cracks. The electronics have been reasonably trouble free but, over time, some of the individual components and, indeed, solder and printed circuit cards have started to fail. Something had to be done, leading to a programme of works known as the Central Line Improvement Project (CLIP), valued at approximately £500 million.
As well as dealing with reliability and obsolescence issues, the programme also includes provision of features to comply with the Rail Vehicle Accessibility Regulations, age related body repairs, and some heavy maintenance activities. Apart from RVAR legal compliance, the project is expected to deliver reduced maintenance cost, a significant increase in reliability and, as a bonus, there is also an expected 120 second reduction in journey time from end to end. Rail Engineer visited London Underground’s Acton Works in November 2022 to see the work in progress.
The scope includes:
- Replacement of the DC chopper system and DC motors with a modern three phase AC traction package. This involves replacing 2,720 traction motors, fitting 680 variable voltage variable frequency inverters, and replacing 340 auxiliary converters. Supplier: Alstom Sweden, motors from ABB Sweden.
- Replacement of the Train Management System (known as DTS) that will help support the passenger information system capturing more data from upgraded systems with automatic download via 4G and station Wi-Fi. Supplier: EKE-Electronics, Finland.
- Upgrade of the passenger information system with in-saloon displays. Supplier: EKE-Electronics/FOCON.
- Install saloon security CCTV using two cameras per car.
- LED lamps requiring less power (to enable PIS and CCTV) and delivering better illumination. Supplier: LPA, UK.
- Modification to provide compliance with the Rail Vehicle Accessibility Regulations 2010, including spaces for wheelchairs to a design by LU.
- Repairing door pillar cracks and floor corrosion on all cars; typically 80-90 welds per two car unit.
- Completing replacement of body ends originally started in 2012.
- Door overhaul (8160 pneumatic door engines and doors).
- Bogie overhaul (1340 bogies).