IET Publication: Guide to Earthing and Bonding for AC Electrified Railways Authors Dr R D White and Allen McDonald - week 4

Week 4 – Requirements for Railway Systems Integration and Engineering Design Process

This is week 4 of a series of 6 Linkedin articles based on the application of earthing and bonding requirements. This article is designed to show the necessity for good engineering management and in particular, the integration of design processes to enable the safe and reliable operation of AC electrified railways. These requirements have been defined and explained in the book.

?The Railway Engineering Management Plan

?The Engineering Management Plan defines how the engineering design is undertaken and implemented. It sets out the engineering management processes, procedures and services which are required to be followed by designers, installers and suppliers.?The following processes are necessary for the design of earthing and bonding:

?·??????Safety Management System (SMS) (To be addressed in Week 5)

·??????Requirements Management Plan;

·??????RAMS (Reliability, Accessibility, Maintenance and Safety);

·??????Interface Management Plan;

·??????Design & discipline plans including the earthing and bonding management plan.

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Systems integration is an integral part of engineering management. Where railway infrastructure projects follow the Engineering Management Plan, the design teams should identify the interfaces and the probability of hazards, enabling system failures to be significantly reduced.

?Requirements Management Plan

?The Requirements Management Plan is a necessary tool for establishing how requirements will be collected, analysed, documented, and managed throughout the lifecycle of a project. Depending on the type of project there may be both project and product requirements. It is easy to fail to document requirements, leave requirements incomplete without a project management tool to properly manage them.

The project Requirements Plan requires the engineering and operational requirements of each discipline. This ensures compliance with project specifications and also with railway & national electrical and safety standards. These requirements normally become the responsibility of the design and build contractor and this will be addressed in more detail in week 6.

?Systems Integration of AC Electrified railways

?Systems Integration is the term given to ensure that the different elements of a railway operate together to achieve consistently safe and reliable performance. It is necessary for electrified systems to be correctly integrated where complex interfaces exist between the high-power traction units or the electrification distribution system, and the low power signalling & communications control systems and radio-based systems. The major cost element of a new railway is the civil construction and the electrical systems are a relatively small portion in comparison. The failure to integrate the electrical systems will probably mean disruption to the whole project during commissioning and delay early operational service. Railway authorities often fail to provide adequate project and engineering integration, placing the whole project programme at risk and this was probably so in the case studies 1,3,4&6.

It has become the norm for railway contracts to be awarded along traditional engineering disciplines thus often leaving the interfaces to be identified and integrated by each contractor. Railway authorities sometimes fail to recognise the complexity of electrical interfaces and do not always provide the mechanism to manage the systems integration between different engineering disciplines.

Examples of interfaces between disciplines or system-wide contracts that need to be identified and integrated include the following:

?·???????????????Rolling stock and AC electrification;

·???????????????Rolling stock and signalling systems;

·???????????????AC electrification with civil structures and station structures;

·???????????????AC Electrification and control & communications systems;

·???????????????AC traction return with LV power systems;

·???????????????AC electrification and DC electrification;

·???????????????Lightning protection system and LV systems.

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The project system integration process should identify the physical, electrical or electromagnetic interfaces through an interface matrix:

?·???????????????Where there is a hazard to humans this should then be recorded in Hazard Log, and the mitigations be recorded in the Requirements Register.

·???????????????Where there is the likelihood of only a disturbance to other systems this should be recorded in the Requirements Register.

·???????????????Where interfaces between systems and contracts create disturbances or hazards discipline designers should prepare an Interface Specification. The Interface Specification defines where the interface exits and then details the engineering design necessary to be implemented. This interface document is required to follow the process between within the project Document Control including the risk register, hazard log and verification and validation process.

?Designing Engineering Systems and Sub Systems

Engineering Managers are required to have an engineering mind capable of understanding the interfaces and coupling mechanisms and who can identify the Hazards and risks to the programme. The system to be delivered is required to be broken down into sub-systems. The interfaces and interactions between the subsystems should be identified and the sub-systems should be designed in sufficient detail to ensure that they will work together as expected and meet the overall system requirements.

The sub-systems of a railway project tend to be aligned with traditional railway disciplines.?For example, an infrastructure system may have signalling and electrification sub-systems, while rolling stock may have train control and traction sub-systems.?However, some single-discipline systems, particularly signalling systems, may be complex enough to be divided into further sub-systems.?The level of detail in the design is dependent upon the disciplines involved and the contractual strategy adopted.

Key-Systems Integration Steps:

·???????????Establish the conceptual design of the system;

·???????????Break the system down into subsystems; this can include multiple contracts;

·???????????Identify the interfaces, intra-system and inter-system; prepare an interface matrix;

·???????????Determine how the subsystems interact, then identify failure modes and degraded modes of operation;

·???????????Design the sub-systems in sufficient detail that it is possible to determine that they will work together as expected and meet the overall system requirements;

·???????????Ensure that the interactions between the subsystems are satisfactory;

·???????????Develop strategies for building the system, validation, installation, commissioning, transition to service, operations, maintenance, decommissioning and disposal;

·???????????Check the system design and associated strategies;

·???????????Keep the system design and associated strategies up-to-date as the project evolves.

?An established method of undertaking technical assurance is to adopt the ‘V Cycle’ process described in EN 50126-1 described below and as shown in Figure 1 – V Cycle Process:

Design Process

·??????Phase 1: Concept

·??????Phase 2: System definition and operational context

·??????Phase 3: Risk analysis and evaluation

·??????Phase 4: Specification of system requirements

·??????Phase 5: Architecture and apportionment of system requirements

·??????Phase 6: Design and Implementation

Installation Testing and Commissioning

·??????Phase 7: Manufacture

·??????Phase 8: Integration

·??????Phase 9: System Validation

·??????Phase 10: System acceptance

·??????Phase 11: Operation, maintenance and performance monitoring

·??????Phase 12: Decommissioning

?This ‘V cycle’ process links the detailed design with the installation and ensures that the test criteria set out in the designs are met during the installation phase.?The link between these activities requires the designer's test criteria to be passed to the installer, and in turn, the installer returns a test plan to show how the criteria have been incorporated into the test plan.?The designer may review the test plan and comment accordingly.

?This ‘V Cycle’ does rely heavily upon the implementation of the Quality Assurance process.

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