With investment in the UK rail network growing but under continued scrutiny to ensure maximum efficiency is achieved, it is essential that the supply chain is able to bring new and innovative technologies and solutions to the market.

Network Rail’s target for investment during CP5, and forward into CP6, is to focus on infrastructure improvements. This covers not only signalling renewal programs but also the introduction of additional electrified routes to support the new trains being supplied as part of the Intercity Express Program (IEP).

Essential to electrification is the control of traction power from electrical control rooms using centralised SCADA (supervisory control and data acquisition) equipment. As a result, Network Rail is investing in a major SCADA renewals program across the electrified network.

Having already worked together on significant integration projects for London Underground, Hima-Sella and Mitsubishi Electric UK saw an opportunity to combine their industry expertise and proven COTS (commercial off-the-shelf) products to design a modern, cost-effective remote terminal unit (RTU) for traction power substation control.

Drawing upon its 42 years’ experience as a system integrator delivering safety critical control applications, Hima-Sella developed the Tracklink® RTU. This uses a traction power control combination of proven ‘COTS’ Mitsubishi PLC (Programmable Logic Controller) software and hardware, plus the design of industry specific interface technologies, to provide a simple and cost effective solution for substation control.

The two companies have subsequently entered into a formal collaboration and supply agreement, designed to ensure long-term commitment to each other and their customers, for the supply and support of the Tracklink RTU solution over its entire asset life. This agreement underpins their pursuit, delivery and long-term support of substation automation projects across the UK.

Technology overview

The Tracklink RTU has been designed to meet the requirements of new and legacy installations as a flexible solution for substation applications. It can be supplied in a single wall mounted or floor standing cabinet or as a distributed solution, and meets the requirements of the modern electrified network and Network Rail standard NR/L2/ ELP/27229 issue 2 – Specification for Remote Control Equipment.

The design encompasses proven applications and consists of a Mitsubishi Electric Q Series PLC, Tracklink interface cards and a panel- mounted HMI (human-machine interface) from Mitsubishi Electric’s GOT 2000 range. All the necessary telecommunications equipment, intelligent device interfaces and battery-backed power supplies are included.

Acting as a slave system to the master control SCADA from which it receives instructions, the Tracklink RTU issues switching commands to the substation equipment and then relays back the plant status as single-bit alarms. Where required, analogue readings can be taken from transducer equipment and relayed to the SCADA to provide voltage and current levels.

Intelligence and control

The Mitsubishi Electric Q Series PLC provides the Tracklink RTU with its intelligence and control. The core PLC build consists of a central processor unit (CPU) together with communications and input/output modules. These modules are fitted to a high-speed backplane to enable fast data transfer between the CPU, I/O and communications modules, and the central SCADA.

The CPU programming was developed using standard function blocks and has been created for the supply of small, medium and large applications. This enables simple mapping of the I/O for each system once the design has been agreed.

A range of communications modules is available to provide a number of options when connecting to the SCADA and other substation devices. These consist of both serial and IP-based solutions that conform to recognised standards for substation automation systems. The Tracklink RTU has been pre-configured to use legacy system protocols as well as DNP3 (Serial /IP), IEC 60870-5- (101/103/104) and IEC 61850.

Intelligent interfaces

A key component in today’s modern substation designs is the role of the IEC 61850 communications standard. Integrating substation devices such
as RTUs, protection relays, circuit breakers and other intelligent electrical devices (IEDs) onto one common IP-based bus network provides a cost- effective solution with a high degree of component interoperability.

Mitsubishi Electric’s C-CPU module can function as both a DNV KEMA- certified IEC 61850 client and IEC 61850 server, utilising both GOOSE and MMS messaging.

The C-CPU module, acting as an IEC 61850 client, will run the application to interrogate the IEDs and relay this information via a DNP3/IP protocol to the SCADA. It is a standard PLC module and can be fitted to the PLC backplane at any time, allowing existing Tracklink RTU installations to be enhanced at a later stage.

RTU key features

The Tracklink RTU solution has been designed not only to deliver the required functionality, but also to implement the following key features and benefits:
» Scalable I/O configurations
» Dummy and mass trip CB options » Distributed I/O applications
» COTS-based technologies
» Dual-processor option
» Reduced installation costs
» Future-proof design
» Interchangeable modules to reduce downtime
» Flexible enclosure design
» Reduced spares holding
» Reduced maintenance costs
» Master-slave architecture
» Multiple protocol implementation (legacy serial, IEC 61850, 60870 and DNP3)
» Battery back-up.

Plant interface and marshalling

To aid in the installation of the Tracklink RTU into new or existing substation installations, dedicated interface cards provide an industry- recognised configuration and point of demarcation. These allow the RTU to be installed using existing plant wiring while delivering the 5kV isolation required to protect the PLC from the substation environment.

Three interface cards provide marshalling and protection for key modules in the system. The Tracklink 10000 card, for the PLC digital input module, comes supplied with 32 individual isolated channels. Each marshalling terminal is fitted with an isolating link and LED for active indication.

The 10001 CO interface card is supplied with 16 relay outputs and 16 individual input channels and works with the PLC digital output module and its corresponding digital input module. Once again, each marshalling terminal is fitted with an isolating link and LED for active indication and the unit is designed for control circuit breakers (CB) and incorporates mass- trip and dummy CB configurations.

Designed for the PLC analogue module, the Tracklink 10002 AI interface card is supplied with 16 individually isolated input channels.

Local-control HMI

The panel-mounted Mitsubishi HMI can be configured to provide a range of features to aid operation, commissioning and maintenance. Standard configurations are supplied with an initial display mode of operation that facilitates instant access to the current status of the plant, including:

» Single line diagram
» Plant status alarms
» Analogue values
» Product documentation and isolation plant drawings
» Control of plant
»  Instantaneous trending of data
»  Historic trending of data
»  Plant statistics and alarm frequencies
»  RTU diagnostics.First year of operation

Commenting on the success of the new unit, and the developing relationship with Mitsubishi Electric UK, Hima-Sella business development manager Chris Elliott said: “The introduction of the Tracklink RTU to the market has been well received. We’ve had a number of units in operation on legacy systems across the routes for nearly 12 months. Achieving Network Rail product acceptance was critical and the support and commitment of Mitsubishi Electric and its technical team to this development was essential.”

David Bean, rail industry sales manager at Mitsubishi Electric UK, added “The combination of Mitsubishi Electric’s proven technologies, offered in a commercial off-the-shelf product with Hima- Sella’s expertise in both safety systems and traction power applications, has resulted in the development of the Tracklink RTU, which is a uniquely flexible, scalable, low-cost solution for modern substation automation applications.”

Hima-Sella and Mitsubishi Electric are continuing to develop the Tracklink RTU application for the rail industry and its potential for use in other markets such as power and water. It is a welcome addition to Hima-Sella’s proven product range which includes Tracklink III for selective door opening applications, Tracklink SCADA, and its Tracklink P2P solution for the control of MOS, NSCD and CTS applications.