EMC (Electromagnetic Compatibility) is an important part of any rail project, be it recommissioning or refurbishing rolling stock, or managing the updates or new builds of depots and stabling facilities.
EMC management, from a risk-based point of view, is something that needs to be carried through all of the stages of a project, ideally from conception to completion. This is the job of the EMC risk assessment.
Making an early start
It is advantageous to the project, and the EMC engineers, for the risk assessment process to start as soon as possible. The risk register results are then updated throughout the life of the project. It is possible to create the risk register at the feasibility or option selection stages, and certainly once the outline of the project is known. This avoids the issues encountered by mitigating risks on already installed or purchased equipment during the commissioning phase.
The difficulty arises when keeping the EMC process up to date throughout the life of the project, as contractors and subcontractors generally change at the different stages. Ideally, the risk register is populated before designs are finalised, then subsequent activities reduce the hazards identified in the risk register to ALARP (as low as reasonably practicable) by the end of the project.
One of the actions possible to reduce risks is on-site measurement, both before and after energisation. The reasons for performing measurements prior to any works include benchmarking the existing emissions so that a comparison may be made with the new installation(s), identifying any particular EM threats at the location for inclusion in the hazard analysis and the design review, and gathering evidence in case future claims are made by neighbours or users regarding interference to radio communications services or other equipment.
Self-interference
Induction from traction current and other HV feeder systems can be modelled and, if an issue is identified, designed out of most railway installations. This is often an important step in reducing the hazards in the risk register, and is of obvious benefit to carry out at a design stage before cabling is installed.
In terms of compatibility, it is of course of vital importance that the signalling systems are not interfered with by both external effects or by the railway itself. In order to ensure that this is unlikely, the risk assessment will highlight any situation that may result in a malfunction of equipment or apparatus. This will then be closed out by subsequent activities, such as procurement reviews or compliance matrices, or by signalling compatibility studies or testing if required.
A final hazard analysis is normally carried out to provide an end-of-project risk register in which all hazards will have either been closed or set to ALARP.
Article written by Dr Rob Armstrong, Consultancy Manager at York EMC Services.
