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INDUSTRY FOCUS RAIL
RAIL SAFETY STARTS WITH EN 50155 Standards are essential for the design and development of safe and reliable power supply products, especially for transportation systems such as railways
P
ower distribution systems on trains, no matter what their purpose, must be safe and reliable, which means complying with
a host of standards including EN 50155. EN 50155 is a European standard that covers electronic equipment used on rolling stock for railway applications, including power supplies. Although the standard was developed for
the European market, it is tied to other safety standards for rail systems (it is the regional equivalent of an international standard IEC 60571) and is the standard that power supplies for rail applications are often designed and tested to. EN 50155 has become increasingly important
as trains have become more technically advanced from an engineering and passenger experience perspective. Onboard Wi-Fi, sophisticated climate control systems, and monitoring sensors, place new demands on electrical systems. This has led to several revisions of EN 50155, ensuring the standards are keeping up with growing complexity.
THE PRIMARY STANDARD EN 50155 covers all of the electronic equipment used for control, regulation, protection, diagnostics and energy supply in rolling stock applications. The requirements placed on this equipment includes operating conditions, product design and documentation, testing, integration, and software. Power supplies and converters, which are needed to provide clean and stable power to all of the electronics found in modern rail applications, fall within the scope of the standard. The key concerns of power supplies in the rail market include supply voltage variation, operating temperature, shock and vibrations, electromagnetic compatibility, and reliability.
REFERENCED STANDARDS Standards don’t exist in proverbial silos, and EN 50155 is no different. It references many other standards that often deal with more specific issues. Some of those standards that especially apply to power supply design include: Fire Safety: The EN 45545-1 standard specifies
materials, construction and testing required to mitigate fire hazards in railway applications. Electromagnetic Emissions: Addressing
electromagnetic emissions and immunity for railway applications, EN 50121-3-2 aims to ensure that equipment does not interfere with nearby devices and is immune from external interference.
Temperature Class
OT1 OT2 OT3 OT4 OT5 OT6
Shock and Vibration Requirements: Electronic equipment and power supplies used on rolling stock for railway applications must be rigorously tested for operating in rugged environments. For the purposes of EN 61373, systems are categorised as carriage-mounted, bogie-mounted, or axle-mounted.
THE EVOLUTION OF EN 50155 As power supply technology has evolved, railways have modernised and safety requirements have changed, EN 50155 has undergone several revisions to keep pace: 1995: EN 50155:1995 2001: EN 50155:2001 2002: EN 50155:2001/A1:2002 2003: EN 50155:2001/Corrigendum Apr. 2003 2007: EN 50155:2007
2010: EN 50155:2007/Corrigendum May 2010 2012: EN 50155:2007/AC:2012 2017: EN 50155:2017 2021: EN 50155:2021 The first revision came in 2001 and included
new requirements for safety management. It also clarified and strengthened existing requirements. The next big update occurred in 2007 and included the addition of three test categories: • Type tests: Verifying a product meets specified requirements
• Routine tests: Verifying a product meets specified requirements after manufacturing process
• Investigation tests: Determine performance outside of specified requirements. The testing provisions in the update require the user to identify any tests subject to agreement at the time of tendering; while the manufacturer is required to provide a test plan listing all the tests to be performed and their specifications. The equipment is not allowed to malfunction or produce a performance which is outside its specification, as per the 2007 update, which also advises only those tests which are necessary must be carried, out as some tests may be costly. Notable changes in 2017 include the addition
of a new reliability test, the ‘Rapid Temperature variation test’, while definitions and illustrations of test conditions were further clarified to allow for more accurate experimentation. The 2017 update adds responsibility with equipment manufacturers and end-users to define operating temperatures for equipment and determine relevant constraints. The most notable update in 2017 was a move to six operating
Temperature Range
-25°C to +55°C -40°C to +55°C -25°C to +70°C -40°C to +70°C -25°C to +85°C -40°C to +85°C
22 DESIGN SOLUTIONS JUNE 2024
Operating Temperature Classes Passenger and driver compartments Equipment in technical cabinets Special applications
temperature classes, as shown in the previous table. The default level is OT3. There is also more flexibility around the length of useful life of all equipment – previously it was 20 years, but as of 2017 there are five classes, beginning with five years. However, level 4 is the default, unless otherwise specified.
Life Class
L1 L2 L3 L4 LX
Useful Life
5 years 10 years 15 years 20 years Special
Useful life classes introduced in EN 50155:2017
A third performance criterion was added in 2021, outlining allowable degradation in the event of a test or environmental disturbance and stipulating that the loss of significant stored data is not permitted. EN 50155:2021 also outlines which type of battery voltage supply systems are permitted.
EN 50155 AND ITS RELEVANCE TO POWER SUPPLIES Power supplies for any type of equipment always influence the design and development of products they’re going into. Standards such as EN 50155 are especially relevant where there are not only stringent performance requirements, but also public safety concerns. The EN 50155 standard applies to many
different aspects of electronic equipment, including installation, control, regulation and protection. All this equipment is integrated into complex systems, operating in complex real-world environments. There are five areas that are crucial when designing power supplies for railway rolling stock equipment: Supply voltage: There are several ways
that power may be supplied to a railway system and this includes both AC and DC supply systems. DC power comes from battery supply systems and is what EN 50155 primarily focuses on. AC power can come from auxiliary power converters, overhead lines or third rail, and are covered in EN 50533:2011 and EN 50163:204 respectively. For battery supplied DC systems the primary
concerns are the battery voltage range, transient voltages, supply voltage interruptions, supply changeover and DC ripple factor. The standard defines a set of nominal battery
voltages that can be selected: 24, 28, 36, 48, 72, 96 and 110V DC, but recommends the use of 24, 72, or 110 V. Limits for various transient and steady state conditions that power supplies must be able to withstand are based on the nominal battery voltage as shown in the next table.
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