Railway Electromagnetic compatibility: EN 50121 standards from EMC

The railway environment is generally considered to be an electromagnetic severe and hostile environment. For an electrified railway , megawatts of electrical power must be converted into propulsion for trains carrying passengers and goods from one destination to another. The train presents an electromagnetic complex environment composed of many systems including signalling, traction, telecommunications and radiocommunications, with exceptionally long distances between equipment or sub-systems, involving cable laying that can be kilometres long on many occasions.

Electromagnetic compatibility (EMC) between electrical and electronic systems is an essential requirement for the reliable and safe operation of the train. For example, it seems clear that interference from traction power equipment can affect the signalling system with potentially serious consequences. Thus, the railway industry endeavours to reduce the risk of such incidents occurring through identification processes and risk mitigation. Electromagnetic compatibility is an essential part of these processes.

The European directive on electromagnetic compatibility

EMC Directive 2004/108/EC has an impact on the whole train , but above all it affects equipment manufacturers. All equipment bearing the CE marking requires the preparation of "technical documentation", equivalent to the Construction Technical File under the previous EMC Directive 89/336/EEC. The manufacturer can choose whether this is assessed by a third-party notified body or not.

It is therefore essential to manage the EMC to meet the technical, security and legal requirements from the start of the project by implementing an EMC Management Plan. Subsequently, tests of EMC must be performed to verify that the requirements of EMC demanded for installation have been achieved.

EMC railway standards

The legally binding Directive of EMC has forced many sectors of the electrical/electronic industry to seriously consider EMC and review the procedures taken to ensure electromagnetic compatibility between electrical/electronic systems and the proper functioning of external radio communications, plus transmission services.

The railway industry has been no exception. Based on the EMC RIA 12 and 18 standards of the Association of the Railway Industry , CENELEC has produced a whole series of EMC standards for railways.

European standards EN 50121, parts 1-5, were introduced in 1995 as previous standards, were adopted in 2000 and 2006 version came into force in July 2009. Manufacturers can evaluate their products with the EN 50121 series of standards, as a means of demonstrating compliance with the Directive.

The key concept of EN 50121 standards is that they seek to achieve electromagnetic compatibility within the railway environment and also confer electromagnetic compatibility between the railway and other electrical and electronic equipment outside the railway environment .

For CE marking of railway equipment, evidence of compliance with EN 50121 standards is mandatory.

EN 50121 series of standards is subdivided into 6 parts, covering different aspects of the railwayenvironment. The structure of the standards and the way they are subdivided has not changed since the original publication. EN 50121 standard comprises the following parts:

• UNE EN50121-1: Railway applications. Electro-magnetic compatibility Part 1: Generalities
• UNE EN50121-2: Railway applications. Electro-magnetic compatibility Part 2: Issuance of the entire rail system to the outside world
• UNE EN50121-3-1: Railway applications. Electro-magnetic compatibility Part 3-1: Rolling stock. Train and complete vehicle.
• UNE EN50121-3-2: Railway applications. Electro-magnetic compatibility Part 3-2: Rolling stock. Devices.
• UNE EN50121-4: Railway applications. Electro-magnetic compatibility Part 4: Issuance and immunity of signaling and telecommunication devices
• UNE EN50121-5: Railway applications. Electro-magnetic compatibility Part 5: Issuance and immunity of fixed power supply installations and associated equipment

Each standard: EMC "basic" standards for measurement methods.

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

The series of standards EN 50121-X represents what CENELEC can agree on in relation to electromagnetic compatibility on railways. Similarly, IEC 62236-X set of standards represents what can be agreed internationally. Despite this, due to the adoption of a wide range of technologies and the retention of "legacy" equipment within railways worldwide, it is clear that these international standards represent the minimum requirement for achieving electromagnetic compatibility and that other "local" measures will be required. In many cases, these national standards are based on the requirements of EN 50121 standard, so the resulting standard more adequately reflects the requirements of a particular part of the railway.

Throughout this compendium of regulations, it is also important to mention EN 50155 standard. This standard for the use in railway applications of electronic equipment used in rolling stock (on-board equipment) is a standard that has caused much confusion among manufacturers over the years. This is mainly because this standard also contains electromagnetic compatibility requirements.

EN 50155 standard was intended to be a product performance standard rather than a standard used for CE marking, mandated by EN 50121 standard. However, EN 50155 becomes a contractual requirement for some manufacturers and, therefore, had to comply with the electromagnetic compatibility requirements of EN 50155 and (generally) EN 50121-3-2.

Management of Electromagnetic Railway Compatibility

To achieve electromagnetic compatibility of railway equipment, we recommend including EMC as a design parameter from the conceptual stage of a project. It is also necessary to control the design process to ensure that documentation is produced. Such documentation will support and be included within the Safety Case to cover the EMC safety aspects and that will allow the manufacturer to declare conformity with the appropriate EMC regulations.

The first stage of this process is to include EMC as a requirement within the technical specifications of the tenders, specifying requirements of EMC . At this stage, you can define the series of EN 50121-x standards in a simple way: 2006 plus appropriate infrastructure standards

The main contractor will produce an EMC management plan, which must be developed at the beginning of the project and could typically include the following:

• A hazard identification (HAZID): an identification of possible 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 that affect or may affect the system.
• A list of references: e.g. appropriate EMC regulations, customer specifications, standards or internal specifications.
• Definition of responsibilities of the main contractor and its suppliers.
• Supplier control: This may include a requirement for each supplier to produce an EMC planand demonstrate compliance.
• EMC management of the whole system.
• Deliverable documentation to conform for compliance.

For a large system, although it will be necessary to carry out some measurements of EMC throughout the system, it is initially necessary to identify the various electrical subsystems and determine the management policy of the suppliers. In this case, a reasonable approach is commissioning each subcontractor to provide documentary evidence to prove that his/her product meets appropriate standards.

As indicated by the management plan, each supplier will be responsible for demonstrating that their equipment meets the specified EMC requirements and will submit their EMC Control Plan , Test Plans and Test Reports to the system contractor, who will include them within the EMC System Technical Documentation .

Immunity testing may be impractical or not feasible at final installation for large systems, and confidence should be placed in the integrity of immunity tests being performed on individual elements of the equipment or systems and the good installation practices used. In this regard, it is important to note that, for European devices carrying CE marking, it is a legal requirement to provide the user with "user information" covering the installation and operation of the equipment.

We are backed by more than 25 years of experience in the design, development, problem solving, laboratory management and measurements in the field of Electromagnetic Compatibility of electronic and mechatronic systems.

Our company Leedeo Engineering is a specialist in Electro-magnetic compatibility and RAMS engineering of the railway sector. We support our clients at any level required for electrical and electronic design tasks, as well as CE marking, both at the level of infrastructure or on-board equipment.