National and International Standards for Harsh Railway Power Solutions
Railway power components must weather harsh conditions in a number of severe environments. Here we discuss the standards governing this space, together with solutions to alleviate the pressure of designing, from the ground up, custom products that meet the bar.
Railway power solutions are needed in many key applications, including passenger accessibility, automated braking, wayside signaling power electronics, and more. Any individual use case that includes railway power solutions will not exist in a vacuum: it will involve varying national and international standards that must be adhered to. These are often specified due to harsh conditions that must be accounted for to a degree that can almost appear to be idiosyncratic. On their own, any of these issues can be problematic, but when taken together, they result in design challenges that can involve extensive testing and potentially delay in time to market.
Selecting power solutions for railway applications, whether it is a chassis mount converter for power electronics or switching regulators for driving aid applications, involves not only rolling stock railway standards but the ability to perform reliably in extremely challenging operating environments.
This article addresses the problem of a vast array of railway power standards specifically related to severe environments and discusses some solutions that alleviate the pressure of designing, from the ground up, custom products that adhere to these standards.
As the railway industry expands and advances, there is a demand for reliable, compliant railway power solutions that can perform in some of the harshest operating conditions. Image courtesy of Pixabay
Railway Power Standards
A railway power solution may need to comply with a number of standards to sell on the international market. The primary standard is EN 50155, the European standard for electrical equipment in rolling stock, covering both functionality and performance. Below is a quick summary of some key standards:
- EN 50155 covers a variety of issues, including voltage variations, surge, temperature, humidity
- RIA12 deals with surge protection
- EN 50121-3-2 covers EMC (Electromagnetic Compatibility) and EMI (Electromagnetic Interference)
- EN 61000-4-2 covers ESD (Electrostatic Discharge)
- EN 61000-4-3 deals with RF (Radio Frequency) immunity
- EN 61000-4-4 covers fast transients
- EN 61000-4-6 deals with conduction immunity
- EN 61373 covers testing for performance under shock and vibration conditions
- IEC 71 and IEC 61373 deal with shock and vibration
- EN 45545 covers fire safety
Additionally, there are national standards to consider, such as RIA 12 (United Kingdom), AREMA (United States), and STM-E 001 (France).
It is noticeable from the summary above that many of these standards deal with the rough operating conditions that affect rolling stock railway power components and systems.
Harsh Operating Environments
As the standards above indicate, when designing railway power solutions, engineers must pay close attention to the climate and conditions of the use environment. These include temperature, shock and vibration, high humidity levels, salt mist, environmental pollution, reactions to fire and smoke, and supply voltage variations.
Rail applications typically involve climates and environments whose temperatures can vary widely and therefore require power solutions that can perform within a range on the order of -40°C to 85°C. However, in some regions of the world, these temperatures may not be able to cover the extremes to be expected, such as excessively frigid areas (like those shown in Figure 2).
The EN 50155 also divides standard device temperatures into classes for easy reference to accommodate regions with different temperatures.
- OT1: -25°C to 55°C
- OT2: -40°C to 55°C
- OT3: -25°C to 70°C
- OT4: -40°C to 70°C
- OT5: -25°C to 85°C
- OT6: -40°C to 85°C
Some areas involve much lower temperatures, resulting in complications when selecting a railway power solution. Image courtesy of Pixabay
Power supplies also need to be at least 85% efficient to reduce the amount of heat they generate. The breadth of extreme temperatures can be difficult to accommodate for, even in the best of circumstances, without the added complication of heat from the power supplies themselves.
Extreme Shock and Vibration
Extreme shock and vibration can be hard on any type of circuit, and they are particularly challenging when it comes to rolling stock where continuous exposure can loosen and disengage electric and electronic components that are critical not only to performance but to safety as well. For that reason, power solutions must be in compliance with EN 61373 Rolling Stock Equipment (which provides details on the testing that must be performed) as well as IEC 71 and IEC 61373 shock/vibration.
Many railway power applications involve exposure to high levels of humidity. To address this issue, EN 50155 requires that power supply technology be designed to handle a yearly average with ≤ 75% relative humidity and 30 days per year consecutively with 95% relative humidity.
Salt Mist and Pollution
Another common issue with railway power solutions is exposure to salt mist and other environmental contaminants. Such environmental contaminants will adversely affect the performance of power solutions, but resistance to these factors can be provided through the use of rugged, IP-rated enclosures.
Resistant to Fire and Smoke
Fire safety is another critical aspect when engineering railway transportation applications, and power solutions must support the safety of everyone involved, both in terms of performance and flammability, smoke generation, and the potential for toxic chemicals to be released.
Fire safety is extremely important for the safety of passengers, conductors, and operators. Image courtesy of Pixabay
The flammability rating for such applications should be UL 94V-0, and the standard related to this particular environmental challenge is EN 45545.
Supply Voltage Variations
Railway power solutions must be resistant to the effects of supply voltage variations. This includes not just voltage variation but also interruptions, surges, and reversal of supply voltage. In short, full electronic protection should be provided, and applicable standards include EN 50155 (Voltage Variations and Surge) and RIA 12 surge protection (3.5VN 20ms)
Additional Key Factors
There are other factors related to power solutions, such as the increasing demand for more power, e.g., a single coach requires 1.5 kW to 2 kW power where it used to require 200-300 W.
One mount type does not work for all applications, which is why a variety of mount solutions is a must when selecting a source for railway power solutions. Image courtesy of Bel Power
High power density, which refers to more power provided in a smaller footprint, answers both the need for higher power capabilities and the need for smaller, more lightweight railway power systems. In addition, more engineers are looking for effective chassis mount solutions such as those shown in Figure 4.
Example: DC/DC Converter
As an example of how railway standards relate to specific power solutions, consider DC/DC converters used with door control switches. These DC/DC converters may be exposed to extreme temperatures, salt mist, and humidity as well as continual shock and vibration loadings. It is also critical that they be resistant to radio interference and exhibit electromagnetic compatibility. And, finally, they must be reliable and safe.
As a solution, consider a 100 W board mount quarter brick DC/DC converter, like the Bel Power RQB-100Y Series. This family of converters meets all the railway standards related to the harsh conditions that have been discussed. The Bel Power RQB-100Y series are designed for use in a variety of railway applications including vehicle control units (VCUs), train control and management systems (TCMS), cab radio units, and door control switches. This product line provides a single output with a wide input voltage from 14 - 160 VDC and an extended operating temperature range.
These ruggedized DC/DC converters meet the EN 50155 and AREMA standards and are in compliance with the following railway-specific standards:
- IEC/EN 61000-4 and EN 50121-3-2 for electromagnetic compatibility
- IEC/EN 61373 Category 1, Class B and AREMA Part 11.5.1 Class C, D, E, I, J shock and vibration standards
- EN 45545-2, HL3 for fire and smoke
In addition, it has met these requirements related to electronic equipment and products
- EN 60068-1, Ad and Ab low temperature start up and storage test at an ambient temperature of -40°C
- EN 60068-2-11, Ka salt mist test, 48 hr duration
- EN 60068-2-30, Db variant 2 cyclic damp heat test, 2 cycles at +55 °C
- CISPR 16-2-1 radio interference standards
Note that it also has an operating temperature range of -40°C to +105°C, which falls within the EN 50155 OT2, OT4, and OT6 standard device temperature classes.
Bel Power Solutions
Severe conditions and strict regulations for performance and testing are a part of developing rolling stock railway power solutions. It is critical that designs include power components that provide reliable performance in their working environments and comply with the relevant international and national standards. Integrating power system solutions that are proven to peform in harsh conditions, comply with regulations, offer high power density, and are available in various mounts, can reduce time to market and shorten testing.
With such a wide range of powered devices in rail applications, there’s not always an optimal off-the-shelf solution. For these cases, Bel Power offers extensive capabilities to modify and customize power supplies so designers can get the most out of their power supplies, no matter the application. Bel Power’s railroad power solutions answer the need for high power density and come in a variety of mounted solutions, meeting industry requirements and complying with the relevant railway standards for your design.