It is all too apparent that interference from traction power equipment may affect the signalling system with potentially dire consequences. Therefore, in the UK, EMC is one of the requirements to be included in the Safety Case for the introduction of new rolling stock, locomotives or track maintenance vehicles. The key EMC problem for the railway industry is the multi-use of the running rails themselves. In the 1840s, the running rails were devised as a simple means of mechanically guiding heavy loads. The advent of the use of electricity prompted the use of 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 coded signals for the signalling system. The interference problem is compounded by the introduction in recent years of inverter driven AC traction motor drives that have to be compatible with, for example, the type 'R' reed signalling circuits introduced in the 1950s operating at 300-400Hz.
The railway environment can be challenging when attaining electromagnetic compatibility.
The legally binding European EMC Directive is incorporated into criminal law in the UK as Statutory Instrument 3418:2006. Railway equipment is not exempt from the EMC Directive, and must comply with it. Building on the Railway Industry Association EMC standards, RIA 12 and 18, CENELEC has produced a series of EMC standards for railways. The European EMC standards EN 50121 parts 1 -5 were introduced in 2000 and have found international acceptance resulting in their implementation in equipment specifications from Hong Kong and Singapore for example. These standards were updated in 2006, and were harmonised in 2007, giving a presumption of conformity under the EMC Directive to apparatus declared to these standards.
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'. Included within this series of standards is the disclaimer 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.
It should be noted that manufacturers are required to produce Technical Documentation which will include test reports and may include an assessment by a Notified Body under the EMC Directive.
Last updated: 2007-Oct-03
