Safety and reliability are hot topics in the UK's rail network, and the power and control system installed in the new Channel Tunnel Link to St Pancras is vital. How will trains be kept on time?
For the first time in over 100 years, a completely new railway is being constructed in the UK. The Channel Tunnel Rail Link (CTRL) is the high-speed line running for 68 miles between St Pancras Station in London and the Channel Tunnel. This ambitious project, costing over £5 billion, has been split into two sections, with the first section due for completion in 2003 and the second scheduled to open in 2007.

Work on section one, which links the Channel Tunnel to Fawkham Junction on the outskirts of London, is now at an advanced stage. Once operational, this will cut journey times from the Channel Tunnel in Ashford to Waterloo by 20 minutes. When fully operational, section one will carry four Eurostar trains every hour and this will increase when Section two comes on-stream in 2007. Being a wholly new railway, developer London & Continental Railways has been able to take advantage of the latest technologies available.

Contract 550 is the £56 million deal for signalling, train control and communications that was awarded to the CCA Consortium (CSEE Transport, Corning Communications and Amey Rail). This incorporates a supervisory control and data acquisition system that will control, via feeder stations, the London Electricity power supply to the CTRL. It will also control and monitor electrical and mechanical elements of the work along the railway. For Chloride Power Protection, the contract has given its Industrial Systems and Telecoms Systems business units the opportunity to demonstrate their respective leading edge uninterruptible power supply (ups) technologies.

The scope of the ups infrastructure includes the provision of dual rectifier systems for signalling, 48 Vdc telecoms ups for 23 sites, together with a Relocatable Equipment Building (REB) at the Ashford Route Control Centre. As well as providing hardware, Chloride Power Protection is handling the maintenance and service for two years using its LIFE 2000 remote monitoring and diagnostics package.

Graham Marshall, who heads Chloride Industrial Systems in the UK, advised that, apart from the two EDP90/600 ups built for the Route Control Centre in Ashford, all of the ups units installed were purpose-designed for the project. The successful development of the dual rectifiers for the signalling systems is a major factor that has already been responsible for the company securing contracts elsewhere in the UK's rail infrastructure.

Termed 'traction supply ups' by Chloride, these units derive power from both the single-phase 25 kV overhead catenary supply and the three-phase 400 V regional electricity company (REC) supply, ensuring constant power for the solid state, interlocking-based signalling systems. These need a very clean ac supply source at all times, which is why the traditional approach of providing power protection on failure of the REC has been to operate a ups and a diesel standby generator.

The availability of the overhead traction supply has always been discounted as a back-up on the grounds that it is electrically dirty, while measurements reveal that the waveform is subject to distortions from high energy spikes, transients, high harmonic content and multiple 'zero crossovers', and there are regular voltage excursions in the range 17-29 kV.

While the 25 kV is a suitable source to derive ac power for traction applications, the quality is wholly unsuitable for electronic signalling systems. The traction supply ups will handle the electrical noise of this supply and the wide voltage variations to provide an ac output that is sinusoidal and stable to 51% of the required supply voltage with less than 5% thd.

Because there is no provision within the ups for the system load to be supplied directly from the 25 kV traction supply, the possibility of this noisy supply being connected to the critical signalling supply load is completely eliminated.

Should a low voltage condition arise, the ups will draw power from the battery until the traction supply voltage recovers. This sharing of the traction power supply and the battery ensures that the nominal ten minute battery is greatly extended. In the event of a serious overload or a fault on the ups inverter output, the ups static switch simply transfers the signalling load to the REC supply without a break in power. The use of a three-phase inverter and static switch to convert the dc battery power to three-phase ac has the effect of simplifying the overall system as it removes the need for a 400/650 V bypass supply transformer.

Power disruptions have been identified as a cause of signals passed at danger, so this new approach to power protection for the sensitive signalling control systems is being greatly appreciated by all in the rail industry. Also welcomed is the fact that this solution effectively eliminates the need for a standby generator set, contributing to lower capital and maintenance costs.

Chloride Power Protection has supplied Amey Rail with traction supply ups for eight locations along the 68-mile route. These are joined by telecoms ups, which have been installed at 23 locations. The units designed for supporting the communications systems give 230 V single-phase and 48 Vdc from the same ups battery, thereby minimising size and complexity.

Completely scaleable and future-ready, these customised energy solutions are based on switch-mode rectifier modules and an innovative three-level monitoring programme for connectivity. Suitable for both 19" rack and ETSI mounting, the units are fitted with 5 A, 10 A, 24 V or 48 V rectifiers and can produce up to 2700 W. Full system monitoring and supervision is accommodated by the inclusion of a Micro Pegase system; this provides local management of the energy station and its environment.

These specialist power systems integrate rectifiers, battery back-up, alarm, distribution and power management systems into space-saving cabinets that can be used for internal or external locations. The result is an integrated solution that delivers a high power to footprint ratio.

The final element in this major power protection strategy is the relocatable equipment building installed at the Ashford Route Control Centre (RCC). This again represents a new departure for Chloride, in that due to space limitations within the RCC, the two EDP90/600 ups and batteries have been put into a purpose-built transportable container. However, the static switch, bypass switch and distribution are located within the RCC. By doing this, should any problems occur within the regional electricity company or cables connecting it to the RCC be damaged, the static switch will continue to operate and support power for the signalling system. This provides the highest levels of reliability possible.

Inkeeping with the rest of the project, one of the ups is powered from the local REC supply and the other from the traction supply. However, at Ashford, this arrangement is a third rail system, as opposed to the other site's overhead line.

The value of this contract to Chloride Power Protection is in the region of £1.54 million, a figure that reflects the considerable amount of product development and co-ordination and its continuing involvement after commissioning in terms of maintenance and service.