Addressing the revised EN50155 regulation governing electronic systems supplied into the rail industry

Author : John Stone | Sales Director | Relec

01 May 2020

Typical examples of railway industry-compliant power conversion products supplied by Relec_580x280
Typical examples of railway industry-compliant power conversion products supplied by Relec_580x280

EN 50155 is the industry standard central to most electronic systems supplied into the rail Industry. October 2017 saw the introduction of a long-awaited revision to the standard.

This article was originally featured in the May 2020 issue of EPDT magazine [read the digital issue]. Sign up to receive your own copy each month.

Specialist power conversion & display technology distributor, Relec Electronics has considerable expertise in providing solutions that are well suited to rail applications – either by ensuring components meet relevant industry standards, or by customising them to match the requirements. As part of its ongoing efforts to maintain its deep understanding of power requirements within the rail industry, John Stone, Sales Director at Relec recently reviewed the revised EN50155 standard...

Much of Relec’s work focuses on applications and requirements for the railway industry, meaning it is crucial that its governing standards are well understood and adhered to. The key changes between EN 50155:2007 and EN50155:2017, with specific reference to power conversion products, are as follows:

EN50155 regulation changes
•    Operating temperature
– there are now six operating temperature classes: OT1 & OT2 for passenger and driver compartments; OT3 & OT4 for equipment in technical cabinets; and OT5 & OT6 for special applications. OT3 (-25 to +70 °C) should be taken as a general requirement, unless otherwise specified. There is also more onus placed on both equipment manufacturers and end users to define exactly what temperatures the equipment should operate in, and what constraints should be observed.
•    Relative humidity – the new standard now references EN50125-1.
•    Battery voltages – details of additional battery voltages of 28V and 36V have now been referenced. There is also tighter definition of the power supply ranges.
•    Interruptions in supply voltage – better definition of a supply interruption, with the addition of a new class (S3 – 20mS).
•    Supply voltages for rolling stock powered by combustion engines – a new section closely defining what ripple factor is likely to be seen on supply voltages.
•    Reliability – the requirements for proof of reliability for end user equipment is much more thoroughly defined, but needs to be agreed between the end user and supplier of equipment.
•    Useful life – previously the useful life of all equipment was deemed to be 20 years, but there are now five classes which can be agreed between end users and suppliers, starting at five years.
•    Insulation coordination – unless otherwise defined by the end user, EN50124-1 pollution degree level two will apply.
•    Capacitance to ground/earth – this is a new clause suggesting that earthing capacitors should always be class Y1/Y2, and be limited to 10nF.
•    PCBs – all PCBs should now comply with IPV-A-610 class two minimum. The use of single sided PCBs has now been prohibited.
•    Protective coatings – more precise definition with three classes of coating, depending on the application, with reference made to IPC-A-610.

New type testing requirements
Low temperature start-up, cyclic damp heat and EMC tests are now mandatory. There is also a new type test called the Power Supply test. This covers the following:
•    supply variations
•    temporary supply dips
•    interruptions of supply
•    supply change over
•    dry heat thermal test – this is now more fully defined and performed over three test cycles
•    voltage withstand test – the test duration for routine tests has been reduced from 60 seconds to 10 seconds

Design guidelines
There is now a comprehensive annex (F), with suggested derating factors for a range of electronic components, and including suggested limits for the values and types of capacitors fitted between ports and ground/earth (10nF max class Y1 or Y2).

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