The management process for EMC at Network Rail

The railway is a highly complex system relying on a vast number of electrical and mechanical components working properly together to keep the 24,000 trains that operate in Great Britain running safely, reliably and efficiently. Every minute, thousands of electrical components are called upon to carry out critical functions to keep services running smoothly and on time.

To help keep all these components working properly, the environment in which these devices operate and the effects of electromagnetic waves, an invisible force that can cause interference and is emitted by all electrical equipment, needs to be understood. Understanding the causes of electromagnetic interference, its effects and, more importantly, how to manage them, is essential to operating and maintaining a reliable railway.

Electromagnetic Compatibility (EMC) is therefore an important aspect that needs to be considered and this overview sets out the management process for EMC at Network Rail and the experience we have gained since it was introduced in 2007. This process is directly influenced by a number of horizontal European directives – the Interoperability, the Railway Safety and the EMC directives and is also integrated into the framework of Network Rail’s Safety Management System.

Problem definition

Electromagnetic compatibility is the capability of an electrical device to function satisfactorily in its electrical environment and not to cause disruptive electromagnetic interference to other equipment. EMC is therefore vital for any electrical or electronic equipment component as part of its integration into the railway system. As such, it requires a suitable management process covering all stages of the life cycle, from design and installation through to maintenance.

Every electrical and electronic piece of equipment can potentially emit interference and be affected by interference. The coupling paths may include physical structures not intended to be part of the circuit, contributing to common mode interference, the effects of which are often very difficult to predict and control.

Owing to these complexities, the phenomenon called EMC is not fully set out or characterised in any standards – European or national. The solutions are inevitably multilayered in several dimensions, often concealed in the designed functionality of the end product.

The new EMC directive 2004/108/EC and Network Rail

The new EMC directive came into force across the EU from 20 July 2007. For Network Rail, as infrastructure manager for Britain’s rail network, the important change concerning the railways is that fixed installations (which most railway assets are) have been brought within the scope of the new directive. Engineers need to be mindful of the available information on the intended use of the constituent parts of a fixed installation and apply good engineering practices so that it meets the essential protection requirements of the EMC directive.

Engineering practices have to be documented, and the documentation held by the person responsible for the installation for as long as it is in operation. The implementation of the EMC regulations does not alter the application of UK legislation regulating the safety of equipment or the safety of railway transportation systems.

The longstanding position of Network Rail is that existing business processes satisfy the requirements of the EMC directive as long as records of the fixed installations are made readily available. Meanwhile, there are questions as to whether Network Rail’s best practices should cover the ‘state-of-the-art’ as required by the new EMC directive 2004/108, considering the age of some of our installations. So, on all active projects, the responsibility for EMC management is with the designated project engineers as the nominated ‘responsible persons’ for the implementation of the directive. Training is provided on a regular basis to familiarise them with the process and the EMC evidence required for compliance.

The nature of most infrastructure upgrades and renewals projects is limited, and it is rare if the entire infrastructure at a given location is modified under the remit of a single project. The new directive sets out the requirements fixed installations must meet when they are put into service, while the guide to 2004/108/EC states that only the ‘changed elements’ of a fixed installation need to comply.

Unchanged apparatus might often include infrastructure that predates June 1998, which has ‘grandfather rights’ and for which the EMI performance is unknown. The fact that it is operational within the environment in which it is used acts as proof that it meets the essential requirements of the EMC directive. Most of the safety critical train-detection systems that have considerable life left have been fully characterised with respect to susceptibility to interference which facilitates the integration of RST and other elements of the railway system.

It is well known that compliance with the European harmonised standard for EMC only provides a presumption of conformity with the EMC directive, the main reasons being the limited frequency band covered and the lack of requirements for degraded but still operational conditions of the equipment under test. In practice, the integration of modern equipment into existing installations isn’t always smooth despite evidence of EMC compliance. In the heavily regulated commercial environment in which the railways operate, this gives rise to extensive investigations and potential financial penalties to compensate any consequential disruption.

The railway safety directive and Network Rail

Network Rail’s safety processes are set up in accordance with the Office of Rail Regulation’s internal guidance and general principles for assessing whether health and safety risks on Britain’s railways have been reduced ‘so far as is reasonably practicable’.

To achieve EMC in the context of safety, the principles of the engineering safety management as laid in the Yellow Book are followed. To satisfy the safety objective of the EMC process, a hazard identification (HAZID) is required. The HAZID should consider all systems and apparatus which might interact electromagnetically with each other. Network Rail operates an integrated risk approach to EMC, so the HAZID is expected to identify whether further or additional testing will be required over and above that specified in the relevant part of the harmonised standard for EMC in the railway environment (BS EN 50121). The impact score from the HAZID is quantified using a set of performance indicators, a mixture of both financial and public measures, which are aligned to the company’s corporate goals.

From an EMC point-of-view, it is crucial for the safe operation of the railway transport system that the integrity of the command and control (C&C) systems is not compromised by interference. Systematic approach to EMI also needs to include the definition of the railway interface to near neighbours and to address personnel safety. To be compliant, installations have to meet safety regulations that require any failure risk caused by EMI to be kept as ‘low as reasonably practicable’ under all normal and foreseen operational degraded modes. Any foreseen failures caused by EMI are obviously not desired and shall be evaluated for their impact on the service reliability.

In the existing regulated environment in which the railways in the UK operate it becomes extremely difficult for any stakeholder to ‘own’ a safety requirement for EMC. The Common Safety Targets (CST) and National Reference Values (NRV) as currently set by the European Railway Agency (ERA) in response to the Railway Safety Directive are defined for the whole railway system, and as such are the responsibility of the Government’s Department for Transport to manage on behalf of the UK.

There are no requirements for EMC defined as part of the CSTs and NRVs as they do not apply to the interface between infrastructure managers and railway operators which is covered by individual contractual arrangements. The current practice under the Railways and Other Guided Transport Systems (Safety) Regulations 2006 (ROGS) for demonstrating compatibility between rolling stock and infrastructure mandates the use of compatibility cases in accordance with the Railway Group Standard (RGS) GE/RT8270. The process for technical compatibility is designed to take away the safety connotation and the role of the infrastructure manager as controlling and accepting authority, in the spirit of interoperability.

The interoperability directive and Network Rail

In the case of interoperability, compliance with a Technical Specification for Interoperability (TSI) in respect of a subsystem to which it is claimed is a legal requirement under European law as implemented in UK. In practice, for EMC to be demonstrated this means that each individual subsystem will also be required to conform to the EMC directive, traditionally by means of complying with a harmonised European standard. In addition, the interfaces between individual subsystems will also need to be defined as compatible, but the TSIs are still silent on the subject. Inevitably, this leads to lengthy arguments when rolling stock is being procured as ‘interoperable’ but the compatibility argument depends entirely on demonstrating the integrity of the infrastructure (mainly train detection systems) installed on the intended route of operation is not compromised, the conditions for which are specified in Network Rail’s company standards.

National standards for EMC

A number of railway group standards exist in the national railway domain and demand compliance in the area of EMC and often cause confusion:

• RGS GE/RT8015 is a national notified technical rule (NNTR), under the interoperability directive. It requires that the EMC safety cases consider all coupling from DC to 2 GHz, but there are no limits defined for various modes of coupling, or reference to other standards that provide the means of meeting this requirement.
• RGS GE/RT8270 sets out requirements for compatibility cases, including EMC and is another NNTR but again, doesn’t contain any limits or methods to derive compatibility.

The compatibility criteria between trains and infrastructure in the immediate future are contained in Network Rail’s existing EMC standards which are advised to be used as applicable in demonstrating compatibility at the point of interface.

The basis for the standards was the Industry Data Initiative (IDI) project which collated evidence from previously endorsed train safety cases in a coherent manner to produce 11 business process documents (EMC standards). Another five standards were added to the suite later, which were developed by Network Rail itself in response to the requirements of GE/R8015, although vehicle manufacturers were kept informed of any emerging requirements in the process of their liaison with Network Rail on emerging submissions. In general, the standards present the established susceptibility limits of equipment, which are translated into rolling stock (RST) parameters via established transfer functions. Different limits apply depending on the applicable interference mechanism.

The standards also provide methodology for demonstration of compatibility in cases when the pass criterion cannot be achieved under all conditions. Because the limits are safety related and dependant on the condition of the rails, these standards cannot be exported to a common domain and remain the responsibility of Network Rail as the infrastructure manager in the UK.

The same constraints apply to the development of EMC rules for interoperability. The TSIs are dedicated to individual subsystems, and as such do not contain safety requirements for the whole system, the responsibility for which remains with the respective National Safety Authorities (ORR in UK). To move away from this position and to support opening the market, ERA, with the support of the railway sector representatives from EIM, CER and UNIFE is working on the introduction of frequency management for future RST and infrastructure subsystems, which will specify frequency bands of operation and corresponding limits and evaluation criteria for measurement.

This approach is similar to the approach taken by the EMC directive. To succeed, it requires that safety related limits are decoupled from the limits published for frequency management. This is only possible if the target train detection system is defined, because the EMC, although fundamental to reliable performance, is only one aspect of it. There is currently a momentum gathering in Europe to define the basic parameters for the target system, of which the frequency of operation and immunity limits are only one basic parameter. Network Rail is proactively engaging in these processes as they will shape the future planning of the railway.

Conclusions

The paper gives an insight into the processes operated by Network Rail to help maintain EMC throughout the operational life of its equipment. By operating an integrated risk management approach to EMC, Network Rail believes it can achieve the ‘so far as is reasonably practicable’ guidelines. Network Rail’s assurance process for EMC provides for consistent following of the engineering safety management principles without leading to over dimensioning of the railway system. Network Rail is proactively engaging with the ERA to facilitate the introduction of frequency management principles at the interface point between RST and train detection systems, hoping this approach will eventually lead to the application of state of the art principles for EMC in the railway environment.

References

The various harmonised international standards quoted in the paper are available from the British Standards Institution and not quoted as part of the reference list.

1. Engineering Safety Management (The Yellow Book), Issue 3, RSSB

2. Directive 2004/108/EC of the European Parliament and of the Council on the approximation of the Laws of Member States relating to electromagnetic compatibility, 15 December 2004, OJEU L/390, 24-37

3. Implementing the new EMC Directive 2004/108/EC in the United Kingdom. Consultation Document, May 2006 URN 06/1141, UK DTI

4. The Railways (Interoperability) Regulations 2006 Guidance, UK DfT

5. The Railways and Other Guided Transport Systems (Safety) Regulations 2006, Guidance on Regulations, April 2006, Office of Rail Regulation

6. GE/RT8270: Route Acceptance of Rail Vehicles including changes in Operation or Infrastructure – Railway Group Standard, Issue 1, February 2003, RSSB

7. GE/RT8015: Electromagnetic Compatibility between Railway Infrastructure and Trains – Railway Group Standard, Issue 1, October 2002, RSSB 8

. NR/L1/SIG/30040: EMC Strategy for Network Rail – Network Rail’s Company Standard, Issue 1, August 2008, NR

9. NR/L2/SIG/30041: EMC Assurance Process for Network Rail – Network Rail’s Company Standard, Issue 1, August 2008, NR

About the Author

Maya Petkova

Maya Petkova is an experienced Railway Signalling System Engineer. She joined Network Rail’s predecessor Railtrack in 2002 and now leads Network Rail’s EMC National Specialist Team. Maya has extensive experience with Train Safety Cases, is a Convenor of the CELELEC working group WGA4-2 developing compatibility limits between rolling stock and train detection systems, for the purposes of interoperability, and she is a nominated EMC Speaker of the Association of European Infrastructure Managers on the EMC Support Group to the European Railway Agency.