FEATURE RAIL
Why poor EMC testing can take rail safety off track
I
n the rail industry, systems must be EMC compliant. The essential
requirements of the EMC Directive state that the equipment shall be designed and manufactured to ensure that the electromagnetic disturbance it generates does not exceed a level above which radio and telecommunications equipment, or other equipment, cannot operate as intended. Also, it is important that it has a level of immunity to the electromagnetic disturbance to be expected in its intended use, allowing it to operate without unacceptable degradation of its intended use.
UNDER THE EMC DIRECTIVE Manufacturers of rail apparatus must prepare and maintain technical documentation, as well as carry out an EMC assessment. This process is then followed by a declaration of conformity and the fixing of the CE marking. The EMC Directive also contains requirements for bespoke equipment intended for permanent incorporation in a fixed installation, which would not otherwise be commercially available. Something like this does not require CE marking, or the raising of a declaration of conformity, with the directive specifying additional documentation requirements.
EUROPEAN STANDARDS Manufacturers of railway apparatus must take into account the Harmonised European Standard EN 50121 relating to railways. This has five parts, which cover emissions of the whole railway system to the outside world, rolling stock, signalling and telecommunications apparatus, as well as fixed power supply installations and apparatus. For apparatus, there is a route to compliance via self declaration with internal
production control and a route nowhere. At the manufacturer’s discretion, an EMC Notified Body provides a type examination of the technical documentation. In either case, the manufacturer is required to produce technical documentation, perform an EMC Assessment, and provide additional information (for identification of the apparatus). For apparatus where the EMC harmonised standards can be applied in full, the resulting EMC test report will form the basis of the technical documentation that the manufacturer is required to keep under the EMC Directive. Where harmonised standards cannot be applied in full (e.g. for rolling stock), then an EMC assessment will need to be made in conjunction with the limited testing that can be performed.
TESTING SITE Ideally, EMC testing will be performed in an EMC test facility, but rail industry logistics are often an issue for large or complex equipment. In such cases it can be tested in-situ, either at the manufacturer’s premises or the final point of installation. Much of the technology being used in the railway sector is tried and tested and available as commercial off-the-shelf (COTS) equipment. However, these may have a lower EMC performance than that specified for rail use in standard EN 50121. Where COTS equipment is used, a gap analysis should therefore be performed against the standards to which the equipment has been tested, and the standard that best represents
the final point of installation. If a gap is identified, additional testing may be required, unless a technical rationale can be used to demonstrate compliance.
Jean-Louis Evans, managing director at TÜV SÜD
Product Service
UNIQUE CHARACTERISTICS Rolling stock also has unique traction supply characteristics, including low frequency emissions that can interfere with signalling. Furthermore, as modern rolling stock uses a wealth of communication and control electronics, it is vital that these perform reliably and safely. Due to health, safety and operational issues caused with performing radiated Radio Frequency (RF) immunity testing outside of an EMC test facility, no testing of this type can be performed on new or modified rolling stock. RF emissions measurements can be made trackside, with the test site meeting the ‘free space’ requirements as far as practicably possible. The type of rolling stock under consideration will determine if emission measurements are made with the rolling stock stationary, or slow moving, and what systems are to be operational. The electromagnetic characteristics of
rolling stock will also change if it has been modified or updated, and for a great deal of rolling stock running with ‘grandfather rights’, the existing EMC characteristics are unknown. Before the modification commences, an EMC assessment survey should therefore be performed, with a further assessment being conducted once all modifications are complete, allowing a gap comparison to be made.
PROVING COMPLIANCE The control of EMC throughout a product development project must be documented, with testing performed against all of the relevant standards. Where this is not possible, a technical rationale and design assessment must be developed to prove compliance.
TÜV SÜD
www.tuv-sud.com
35 MARCH 2017 | ELECTRICAL ENGINEERING
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64
