EMC and Railway Safety

The railway environment is generally regarded as a “severe” electromagnetic environment. For an electrified railway, Megawatts of power are required to be converted into the propulsion of trains in order to transport passengers or freight from one destination to another. The railway presents a complex electromagnetic environment made up of many systems including signalling, traction, telecommunications and radiocommunications.

Electromagnetic Compatibility (EMC) between electrical and electronic systems is an essential requirement for the reliable and safe operation of the railway. It is all too apparent that interference from traction power equipment may affect the signalling system with potentially dire consequences. The railway industry strives to reduce the risk of such incidents occurring through processes of hazard identification and risk mitigation. Electromagnetic compatibility forms an essential part of these processes. So in the UK, EMC is one of the requirements included in the Safety Case for the introduction of new rolling stock, locomotives or track maintenance vehicles onto the rail network.

The key EMC problem for the railway industry is the multi-use of the rail itself. In the 1840s the rails were simply a mechanical guidance system. The advent of electricity prompted the signalling engineer to invent train detection systems within track sections, involving using the rail as an electrical conductor. Today we have the situation where the rail is the guidance system, the return power conductor in ac or dc railway electrification schemes and is also being used as a conductor of low power level coded signals for the signalling system (track circuits). The interference problem is compounded by the introduction in recent years of inverter driven ac traction motor drives that have to be compatible with “legacy” equipment, for example in the UK, the type “R” reed signalling circuits introduced in the 1950s operating at 300-400Hz.

The European EMC Directive
The EMC Directive (2004/108/EC) [1] and, for example, the implementing UK regulations (SI 2006 no. 3418) [2], have an impact on the whole Railway. The railway is defined as a “fixed installation” under these regulations and the “good [EMC] engineering practices” used for the installation of equipment must be documented and held by a “responsible person” and be available to the enforcement authorities whilst the fixed installation remains in operation. The definition of “responsible person” will affect contractors and infrastructure controllers; it will require clarification in contracts for the hand-over of responsibility and of documentation.

Whilst the EMC Directive itself is not a “safety” directive, the management of the EMC documentation provides for a record to be maintained of the EMC of the railway and as such provides a model that can be adopted outside of Europe.

The Directive also affects equipment manufacturers. All equipment carrying the CE marking requires “technical documentation” to be prepared, equivalent to the Technical Construction File under the previous EMC Directive 89/336/EEC. The manufacturer, at his option, can choose for this to be assessed by a third party Notified Body.

It is therefore essential to manage EMC to meet the technical, safety and legal requirements from project concept by implementing an EMC Management Plan. Subsequently EMC testing must be carried out to verify that EMC has been achieved.

EMC Railway Standards
The legally binding EMC Directive has forced many sectors of the electrical/electronics industry to consider EMC and to review the procedures taken to ensure EMC between electrical/electronic systems and the correct operation of external radiocommunications and broadcast services; the railway industry is no exception. Building on the Railway Industry Association EMC standards RIA 12 and 18, CENELEC has produced a whole raft of EMC standards for Railways.

The European EN 50121 parts 1-5 [4] were introduced in 1995 as pre-standards, were adopted in 2000 and the 2006 version became fully effective from July 2009. Manufacturers may assess their products against the EN 50121 series of standards as a means of demonstrating compliance with the Directive. These standards have also found international acceptance resulting in their implementation in equipment specifications from Hong Kong and Singapore for example.

The key concept of the EN 50121 standards is that they attempt to achieve EMC within the railway environment and also confer EMC between the railway and the “outside world.” The disclaimer is included within this series of standards that EMC is likely to be achieved if the standards are met, but that, because of the complexity of the environment, EMC cannot be guaranteed.

The 50121 series of standards is subdivided into 6 parts, covering different aspects of the railway environment. The structure of the standards and the way in which they are subdivided has not changed since the original publication.EN50121 comprises the following parts:

  • EN50121-1 General
  • EN50121-2 Emission of the whole railway system to the outside world
  • EN50121-3-1 Rolling stock – Train and complete vehicle
  • EN50121-3-2 Rolling stock – Apparatus
  • EN50121-4 Emission and immunity of signalling and telecommunications apparatus
  • EN50121-5 Emission and immunity of fixed power supply installations and apparatus
  • Each standard calls up “basic” EMC standards for the measurement methods.

It should be noted that EN 50121 parts 2, part-3-1 and part 5 require “on-site” testing where the measurement environment does not have the same degree of control as for laboratory testing.

The EN 50121-X series of standards represents what can be agreed in relation to EMC in railways by CENELEC. Similarly the IEC 62236-x series of standards represents what can be agreed at an international level. However, because of the adoption of a wide range of technologies and the retention of “legacy” equipment within railways around the world, it is apparent that these international standards represent the minimum requirement to achieve EMC and that other “local” measures will be required. In many cases, these national standards build on the requirements of EN 50121 such that the resulting standard more adequately reflects the requirements of a particular part of the railway.

In 2002, Network Rail and the Railway Standards and Safety Board (RSSB) published a new group standard; GE/RT 8015 – Electromagnetic Compatibility between railway infrastructure and trains. This standard mandates the requirements for the management of EMC between the railway infrastructure and trains to enable safe operation to be assured.

Similarly, in 2000 London Underground Limited (LUL) published its own EMC standard and in particular document M1027 A2, a manual of EMC best practice, which defines and clarifies the key EMC requirements for all types of new, modified and “off the shelf” systems. It also defines the requirements for the EMC Control Plan, Test Plan and Test Reports. The latest versions of these LUL documents are respectively: standard 2-01018-001/1-222 A1 and manual of best practice 5-01018-001/G-222 A1

EN 50155 – Railway applications: Electronic equipment used on rolling stock is a standard which has caused much confusion over the years with manufacturers, primarily because this standard too contains EMC requirements.

The intention of EN 50155 was that it would be a product performance standard rather than a standard used for CE marking purposes; that was the remit of EN 50121. EN 50155 was, however, a contractual requirement for some manufacturers and therefore had to meet the EMC requirements of both EN 50155 and (usually) EN 50121-3-2.

The Railway as a Fixed Installation
Fixed installations (FIs) are assemblies of various apparatus and other devices, carrying the CE Marking, installed and/or constructed “applying good engineering practices” and intended to be used permanently at a pre-defined location within the EU (e.g. electricity distribution networks, telecoms networks, large machinery and assemblies of machinery on manufacturing sites). An FI is not subject to conformity assessment, but it must, however, meet the protection requirements. The “good engineering practices” shall be documented and the documentation held by “person(s) responsible” for inspection by the national authorities for as long as the FI is in operation.

The railway clearly meets the definition of a fixed installation.

The Competent Authority may request evidence of compliance of the FI with the protection requirements and, when appropriate, initiate an assessment. Member States are required to set out the provisions for the identification of the person(s) responsible for the compliance of a FI; this is simply reinforced by the Commission’s guide to the directive [3]. Under the UK regulations a “responsible person” means “…in relation to a fixed installation, the person who, by virtue of their control of the fixed installation is able to determine that the configuration of the installation is such that when used it complies with the essential requirements” [2]. If a FI is identified as an unacceptable source of emissions, a Competent Authority can request that the responsible person bring it into compliance with the protection requirements.

Since the constituent apparatus of the fixed installation will conform to the EMC Directive and this conformance is likely to have been demonstrated by compliance with harmonized standards, then, the Commission argues, the EM environment of the fixed installation is defined, allowing for addition of apparatus employing “rapidly changing technologies” itself conforming to harmonized standards. This is consistent with the EN 50121 standards [4], which cover all the constituent parts of the railway.

Where apparatus is designed and built for incorporation into a specific FI and is not otherwise commercially available, it is not required to undergo formal conformity assessment procedures. The manufacturer may choose to either follow conformity assessment procedures or to provide accompanying documentation detailing the name and site of the FI and the EMC precautions to be taken for the incorporation of the apparatus in order to maintain the conformity of the installation. The manufacturer must also provide identification of the apparatus and his name and address, or the name and address of his authorized representative (if the manufacturer is outside the EEA) or the person within the Community responsible for placing the equipment on the market.

1005_F2_photo2

The Impact of the FI Requirements on the Railway
Railway infrastructure controllers will need to appreciate the implications and implement policy.

In the case of new build the “responsible person” will be the Prime Contractor who will oversee and coordinate all collaborators/suppliers, EMC installation and approvals documentation. After commissioning and hand-over, the infrastructure controller will become the responsible person e.g. Chief Engineer/Technical Director, who will arrange to hold all the EMC documentation. This documentation will be “living” documentation; as upgrades occur, information will be added.

For existing build, the new EMC Directive is not retrospective. Therefore the EMC documentation will be built up over time by upgrading project documentation, plus any existing data/documentation.

So the questions remaining are:

  • How will it be put into practice?
  • Will there be enforcement?
  • Are there benefits?

Suggested scenarios for possible implementations have been outlined in the article.

Enforcement action seems unlikely, since Competent Authorities have shown little appetite to enforce the EMC requirements for products. The latter should actually be easier under 2004/108/EC with the new requirement for Technical Documentation (TD) retention, as authorities can demand to see the TD, not just a Declaration of Conformity (DoC). We shall wait with interest!

There are benefits. The FI requirements lend weight to the need for a structured approach to EMC encompassing safety aspects, interoperability and EMC Directive conformance. This model can clearly be used in non-EU countries as a means of demonstrating EMC assurance for railways.

It should be noted that the FI regulatory regime came into effect in July 2007. The FI documentation, based on recording “good engineering practices,” includes initial EM site surveys to benchmark the environment, EMC Management Plans, hazard identification, the use of compliance matrices and in many instances on-site testing to verify that the measures undertaken ensure that EMC has been achieved.

EMC Management
In order to achieve EMC for railway equipment it is necessary to include EMC as a design parameter from the concept stage of a project. It is also necessary to control the design process to ensure that the documentation is produced which will support and be included within the Safety Case to cover the EMC aspects of safety and which will enable the manufacturer to declare conformance with appropriate EMC regulations.

The first stage of this process is to include EMC as a requirement within the Invitation to Tender (ITT) and to include an EMC specification. At this stage it may simply define the EN 50121-x:2006 series of standards plus the appropriate infrastructure standards eg RSSB Group standards such as GM/RC 1500, GM/RT8015 or the London Underground standard 2-01018-001/1-222 A1 and manual of best practice 5-01018-001/G-222 A1.

The main contractor will then produce an EMC Management Plan (also known as an EMC Control Plan or EMC Strategy Document) which should be drawn up at the commencement of the project and typically will include:

  • A hazard identification (HAZID): an identification of the likely sources of interference from the equipment that will affect other equipment in the operating environment; an identification of the sources of interference in the environment affecting or likely to affect the system;
  • A listing of references: for example, the appropriate EMC regulations, customer specifications, standards, or in-house specifications;
  • The EMC management rationale;
  • Definition of responsibilities of the prime contractor and his suppliers;
  • Control of suppliers: this may include the requirement for each supplier to produce an EMC plan and to demonstrate compliance;
  • “Whole system EMC management,” declaring the overall intention of managing EMC by design, identifying particular areas of concern;
  • Deliverable documentation;
  • EMC time management: identification of milestones e.g. on-site whole system EMC emission tests, for incorporation into whole project plan.
  • Appended to the EMC Management Plan will be the EMC design guidelines and practices used by the prime contractor.

For a large system, whilst it will be necessary to perform some EMC measurements on the whole system, initially it is necessary to identify the various electrical sub-systems and determine the procurement policy from suppliers. In this instance a reasonable approach is to task each sub-contractor with providing documentary evidence that his product is compliant with appropriate standards.

As indicated by the management plan, each supplier will be responsible for demonstrating that his equipment meets the EMC requirements specified and will submit his EMC Control Plan, Test Plans and Test Reports to the system contractor who will include these within the system EMC Technical Documentation. It is then necessary for the system manufacturer to validate, from an EMC viewpoint, the installation and wiring techniques he has used. This will be partly by reference to the management plan, which lays down the essential EMC working practices, by reference to the Quality Assurance procedures for the contractor’s organization, but also verification, by whole-system EMC emission tests.

Immunity testing may be largely impractical on-site for large systems and reliance must be placed on the integrity of the immunity testing performed on the individual items of apparatus or systems and the installation practices used. It is vital that the installation practices must ensure that the integrity of the sub-system immunity is maintained, whether by using for example, screened cables, cable separation, or grounding and bonding techniques. Hence good communication is required between supplier and main contractor to ensure the flow of information. It should be noted that for European apparatus carrying the CE Marking it is a legal requirement to provide the user with “user information,” covering installation and operation of equipment.

1005_F2_photo1

A Novel Technique for Measuring Emissions from High Speed Trains
The EN 50121-2 and EN 50121-3-1 require emissions to be measured from moving trains from a single observation point at the side of the railway. The measurements need to be made using a peak detector since the “window of opportunity” to make the measurement is very small and is derived from the beam width of the antenna, the scan rate of the measuring instrument and the speed of the train. This means that transient emissions, such as those due to pantograph bounce or shoegear gapping are included in the actual measurement.

The standard limits are derived from such measurements which mean that potentially a manufacturer of rolling stock can produce continuous emissions up to these limits and so we may have “noisier” trains than in the past! Also the standards require individual train passes for different frequency ranges, a time consuming and expensive operation, usually requiring the measurements to be made on a test track or on the network during a possession.

Conclusions
For EMC assurance for equipment or large installed systems, within the railway environment, a practical approach has been described which relies on rigorous testing of sub-systems and the verification of installation and design practices by a combination of managing EMC from the outset, QA procedures and whole system emission testing accepting practical limitations.

This approach can be seen to fulfill demonstration of the essential protection requirements of the EMC Directive, in Europe, in relation to effect of the system on the external environment, the need to control the internal EMC within the system and the manufacturer’s need to satisfy a court that he has used all due diligence to avoid committing an offence.

Further the EMC Technical Documentation and the incorporated test data can be used to support the EMC aspects of the equipment/system Safety Case and in the case of signalling projects, for example, the documentation can be added to the EMC “Fixed Installation” documentation for the railway. It must be stressed that the railway EMC standards represent the minimum technical requirement and that additional measures may need to be taken on the basis of the hazard identification and risk closure.

The technical difficulties of making EMC measurements on moving trains have been addressed and a cost effective solution referred to. favicon

Acknowledgements
The authors gratefully acknowledge access to information held by York EMC Services Ltd, University of York. They also acknowledge the experiences gained from YES Ltd customers who have successfully prepared Technical Documentation and TCFs for conformance with the European EMC Directives and have used test data to close out the EMC issues raised in Hazard Logs.

References

  1. Directive 2004/108/EC of the European Parliament and of the Council of 15 December 2004 on the approximation of the laws of the Member States relating to electromagnetic compatibility and repealing Directive 89/336/EEC, Official Journal of the European Union (OJEU) L 390/24 dated 31.12.2004, pp24 – 36.
  2. “The Electromagnetic Compatibility Regulations 2006,” Statutory Instruments 2006 No. 3418, December 2006.
  3. “Guide for the EMC Directive 2004/108/EC,” EMC WG of the European Commission, 22 March 2007.
  4. “Railway applications – Electromagnetic Compatibility,” EN50121-X:2006 (5 parts), CENELEC, 2006.
  5. “EMC in Railways,” Course Notes, C.A.Marshman, York EMC Services Ltd.
  6. “Improved Measurement of Radiated Emissions from Moving Rail Vehicles in the Frequency Range 9 kHz to 1 GHz,” AJ Rowell, D Bozec, S A Seller, L M McCormack, C A Marshman and A C Marvin, IEEE EMC Symposium 2004.

Chris Marshman is the Managing Director and Nick Wainwright the Operations Director of York EMC Services Ltd, operating three UKAS accredited EMC testing laboratories and BIS appointed Notified Body. YES Ltd provides EMC consultancy, testing and training services to the railway industry. They can be reached by phone at +44(0)1904 434440 or at enquiry @yorkemc.co.uk.

About The Author

Related Posts

X