REGISTER

Victor G. Abbott B.E (Elec), M.B.A (Tech Mgt), MlRSE

Project Manager, Foxboro Transportation, Invensys Rail Systems

Today's railway control systems provide a spectrum of functionality and are essential for railway operators to meet their key business and performance objectives.

Supervisory Control and Data Acquisition (SCADA) systems are an ever increasing class of control system used in the railway environment, not only for the traditional traction power control function, but also as the platform for integration of modem railway control and communications system applications.

Rail SCADA customers demand that these systems not only provide the desired functionality but also achieve desired safety integrity levels. Although SCADA systems are rarely relied on to provide the sole mitigation against high risk hazards, they are frequently used to contribute to the management of hazardous situations, or to implement partial defences. As such, in some applications, SCADA systems are safety-related systems (as opposed to safety-critical systems) and are nominally considered as SE 1 or 2 systems.

Development and safety requirements for these middle integrity systems are often conflicting. On one hand, customers demand extensive functionality using standard, Commercial-Off-The- Shelf (COTS) products and want the cheapest price. On the other hand, in determining the safety integrity requirements of a SCADA system, the SCADA system vendor must take into account the environment in which the system is to be deployed, consider the availability of other hazard defence mechanisms, and engineer a cost-effective solution.

Moreover, cost-effective safe solutions are a must for the rail-based transportation task to thrive in a fiercely competitive world whilst providing increasing levels of safety. Based on the work by [Atchison & Grifiths 20021 this paper discusses the issues involved in engineering a SCADA system product for use in modern railway environment addressing the associated safety-related criteria. This paper is organised as follows:

• Section 2 - discusses railway operational requirements and control systems used in the railway environment.
• Section 3 - describes SCADA systems architecture and use in rail applications,
• Section 4 - discusses SCADA system safety and impact in rail applications,
• Section 5 - discusses the approach to SCADA engineering and issues associated with safety assurance,
• Section 6 - provides a proposed solution for engineering SCADA systems.
• Section 7 - briefly outlines Foxboro's experience with systems and safety assurance.
• Section 8 - provides an overall conclusion and summary of the paper.