ABB explains how a smart automation approach to software and hardware is helping Network Rail achieve its vision of electrification for the Great Western Electrification Programme (GWEP)
In 2014, ABB and its partner UK Power Networks Services were appointed to deliver the trackside power infrastructure for the Great Western Route Modernisation programme. The overall goal is to enable more reliable, green and smooth electric train travel for communities along the Great Western route.
During the project, ABB’s scope includes designing and delivering 31 trackside feeder substations along 235 miles of electrified track between London Paddington and Cardiff. These receive power from National Grid’s 400 kilovolt (kV) network and step it down to a 25-0-25 kV power supply for catenary lines.
The conventional approach to rail electrification is to divide the railway line into sections, each of which is controlled by at least one circuit breaker.
However, Network Rail’s design engineers spotted the potential to reduce the level of investment during the early GRIP (Governance for Railway Investment Projects) stages of the project by using load break switches instead of circuit breakers in some instances. These load break switches would also control the flow of electricity but are less costly than circuit breakers. This is because unlike circuit breakers, load break switches are not designed to tolerate high-level fault currents.
RATS CONCEPT
To enable the use of load break switches, Network Rail created a new concept called the Rationalised Autotransformer Scheme (RATS). This is a novel approach to protection and control based on IEC 61850 smart grid communication. Under RATS, load break switches are protected from ever experiencing high-level fault currents by circuit breakers. These are controlled by Intelligent Electronic Devices (IEDs) that will open circuit breakers when a fault is detected.
In the case of a fault, communication between the IEDs will identify its location to within a few kilometres. The scheme will then reconfigure the network to isolate the fault and re-connect healthy sections of track. A three-stage process of tripping, reconfiguration and restoration must all take place within a few seconds.
The RATS concept minimises the length of track affected, as well as the resources needed for inspection, rectification and restoration of power to the railway lines. The overall result is less outage time and shorter possessions, with less risk to operating staff working along the rail corridor.
The RATs concept can be achieved with digital communication over fibre-optic lines based on the IEC 61850 protocol. This is the international standard that governs the protection and control of substation automation equipment. It is based on the philosophy of using a single future-proofed communication protocol, a common format for storing data and compatibility across equipment that has been supplied by different vendors. IEC 61850 makes use of GOOSE (Generic Object Oriented Substation Event) messaging, which is a controlled messaging mechanism where data is grouped into a data set and transmitted within four milliseconds. ABB’s deployment of the scheme will make use of around 800 IEDs at 31 substations to protect and control the power supply to four electrified tracks. These control communication between the equipment serving each substation and between individual substations using Network Rail’s fibre optic Fixed Telecom Network. During the project, ABB is installing the IEDs and accessories into protection and control cubicles which are installed inside Auxiliary Equipment Enclosures (AEEs), which are delivered to site ready to plug and play.
FACTORY TESTING AND VERIFICATION
An important element of the project was an extensive testing and verification process carried out at ABB’s facility in Stone, Staffordshire. This ‘transportable commissioning’ philosophy means that the RATS protection and control equipment was only delivered to site after being configured and commissioned under controlled factory conditions.
The bench testing typically took place with equipment for around six substations at once, featuring more than 100 IEDS at a time in 40 test racks and evaluating the system response to around 100 possible scenarios.
The approach enabled a high level of quality control. Test engineers used a dedicated test set to mimic real-life conditions on the network and evaluate the response. The status of circuit breakers, disconnecting switches, earth switches and load break switches was programmed into the IEDs, with no need for any external hardware simulators.
In addition, the real-life performance of the devices was programmed into the IEDs in terms of tripping and closing times, and the timing of test sets was synchronised. This was used to ensure realistic evaluation of time taken to complete the automation sequence for each scenario.
The verification team then carried out de-bugging and troubleshooting for each scenario by using the data from timestamped event lists. A structured approach helped the team overcome the challenge of analysing a large number of GOOSE messages and logical combinations from multiple IEDs in the complex network.
Ultimately, the bench testing demonstrated that the protection and control scheme could successfully complete automatic fault detection and clearance within a few seconds. After this, the scheme will hand over to a human operator to evaluate the fault and initiate manual inspection and rectification.
The process has demonstrated that offline verification is an effective way to mitigate project risk before delivery to site And it has been shown to reduce the overall final commissioning time on site.
MODULAR AND ENVIRONMENTALLY FRIENDLY SWITCHGEAR
From a hardware perspective, ABB developed a new approach for GWEP in the form of its SMOS (Structure Mounted Outdoor Switchgear) Light. This modular switchgear is designed for straightforward installation and maintenance at trackside substations.
The switchgear is delivered to site as modules that are ready to plug and play. It integrates all the components required to isolate the power supply to the catenary line and to sectionalise individual parts of the track for maintenance and inspection. Individual components include the Network Rail PADS approved FSKII+ 25kV circuit breakers and disconnector as well as current and voltage transformers, all factory-mounted on a steel structure.
Integrating the FSKII+ into the SMOS Light concept has reduced project risk and cost in the construction phase of rail electrification projects. It saves time on-site by up to 30 percent as there is no need to install and commission separate components.
SMOS Light switchgear has also been adopted on the Crossrail project in London, where it has been installed on network traction substations on the western and eastern surface sections of the route.
Once in operation, the switchgear has high reliability and is maintenance-free as it uses the FSKII+. This is a robust and well-proved vacuum circuit breaker that combines a magnetic actuator and electronic controller. The breaker has achieved more than 10,000 operations under test conditions, which is equivalent to a service life of more than 20 years.
A major benefit for Network Rail is its use of vacuum as an insulating medium. This eliminates the need for SF6 gas in trackside substations. As this gas has an elevated global warming potential, adopting vacuum-insulated switchgear supports the operator’s environmental credentials.
While RATS was developed for use with autotransformer systems, the concept provides significant efficiencies for both classic 25 kV and autotransformer 25-0-25 kV system designs. Network Rail is looking at how this may be employed to reduce electrification costs on new systems.