Electronic components used in railway applications must meet strict requirements defined by standards such as EN 50155 (product standard) and EN 50121‑3‑2 (EMC). These standards specify all technical, environmental, and safety criteria that electronic equipment must fulfill to be approved for use in rolling stock. The current version of EN 50155 (2021) spans roughly 130 pages and covers a wide range of performance and reliability requirements.
When selecting a power supply, it is crucial to understand which characteristics a DC/DC converter must inherently provide, which requirements are mandatory, and why a power supply designed merely for industrial use is not sufficient for reliable operation in trains.
Railway applications also differentiate between installation locations—passenger cabins, machine rooms, outdoor cabinets, bogies, equipment boxes, etc. Each location corresponds to different environmental classes defined in EN 50155.
The standard also defines operational behavior criteria, classified into A, B, and C, similar to industrial power supplies:
- Criterion A: No degradation of function or performance during disturbances
- Criterion B: Normal operation must resume after the disturbance; temporary degradation is allowed
- Criterion C: Temporary functional loss is permitted, but automatic or manual recovery must be ensured
Environmental Requirements
Altitude
According to EN 50125‑1, operation up to 2000 m above sea level is considered standard unless otherwise specified in the datasheet.
Temperature Classes
DC/DC converters must meet defined operating temperature classes from OT1 to OT6 (−25 °C to +55 °C up to −40 °C to +85 °C). If no class is specified, OT3 (−25 °C to +70 °C) applies by default.
Important considerations:
- The converter’s internal temperature can be 10–15 °C higher than ambient temperature.
- Additional short‑term temperature classes (ST0–ST2) define permissible temperature peaks.
- Rapid temperature changes (e.g., entering/exiting tunnels) must be tested according to specific change‑rate classes.
Shock and Vibration (EN 61373)
Railway electronics must withstand extreme mechanical stress:
- Vehicle body (Category 1, Class B): up to 1.01 m/s² (0.1 g)
- wheel set (Category 3): up to 38 m/s² (3.8 g)
- Lifetime vibration tests: 0.6 g to 14 g depending on installation
- Shock tests: 5 g to 100 g
This requires robust mechanical design and component selection.
Humidity
Cyclic humidity and condensation tests are mandatory and part of the type test.
Electrical Requirements
Input Voltage Behavior
Typical railway supply voltages: 24 V, 72 V, 110 V.
Requirements include:
- Continuous voltage range: −30% to +25% (Criterion A)
- Short‑term tolerance: ±40% for 0.1 s (Criterion A)
- Overvoltage: +40% for 1 s (Criterion B)
- Supply interruptions:
- Class S2 (10 ms) is standard
- If unspecified, S2 applies by default
- For 30 ms interruptions, C1 or C2 may be required
Reliability & Useful Life
EN 50155 defines reliability expectations. If not specified, a useful life of 20 years (Class L4) is assumed.
Design Requirements
EN 50155 also influences the design process:
- ISO 9001 certification is mandatory
- Transparent, auditable design documentation
- Protection against faults, inrush current, and reverse polarity
- Conformal coating is required unless technically impossible
- Fans are discouraged; if used, failure must not cause damage
- Clear identification (serial numbers, revision levels) is required
Testing Requirements
Manufacturers must provide three types of test reports:
- Type Test Report – proves suitability for railway use
- Routine Test Report – verifies each individual unit
- Investigation Test Report – documents additional operational behavior
Mandatory type tests at 25 °C: | Optional tests:
| Mandatory spot check:
|
visual inspection | Storage at low temperature | visual inspection |
Operating behavior (functional requirement) | IP-Code | operational behavior |
| Checking the DC power supply | stress | Insulation test (10 seconds) |
Operation at low temperature | Rapid temperature changes |
|
Operation in dry heat | salt spray test |
|
Insulation test (up to 2.2 kV for 1 minute, depending on input voltage) |
|
|
Cyclic humid heat (according to EN 60068-2-30) |
|
|
EMC |
|
|
Vibration and shock testing (EN 61373) |
|
|
Fire Protection (EN 45545‑2)
Fire safety is classified into Hazard Levels HL1–HL3, depending on vehicle type and operating environment (e.g., metro, regional trains, high‑speed trains).
For DC/DC converters:
- PCBs are classified as EL 9 and require fire testing
- Open‑frame converters typically require:
- R24, T01 (oxygen index)
- R25, T16 (glow‑wire test)
- R26, T17 (small flame test)
- Potted modules require additional grouping evaluations due to encapsulation materials
Here is an overview of the trains and their requirements:
operating class | design class | |||
N: | A: Vehicles for automatic driving, without emergency personnel | D: Double-decker vehicles | S: sleeping car | |
1 Vehicles that are not designed for underground sections (tunnels) or elevated sections. Above-ground road traffic, e.g., trams | HL1 | HL1 | HL1 | HL2 |
2 Vehicles designed for underground sections (tunnels) or elevated sections must be able to reach emergency stations or train stations within a short travel time (<5 km). e.g., metro, subways, regional trains | HL2 | HL2 | HL2 | HL2 |
3 Vehicles designed for underground sections (tunnels) or elevated sections must be able to reach emergency stations or train stations within a reasonable travel time (>5 km). e.g., IC, ICE | HL2 | HL2 | HL2 | HL3 |
4 Vehicles designed for underground sections (tunnels) or elevated sections without the possibility of evacuation. e.g., suspension railways, London Underground | HL3 | HL3 | HL3 | HL3 |
At the customer's request, additional requirements may arise, which must then be agreed upon between the manufacturer and the customer.
EMC Requirements (EN 50121‑3‑2)
Railway EMC limits are significantly stricter than industrial standards.
Examples:
- Conducted emissions: 150 kHz–30 MHz
- Radiated emissions: 30 MHz–6 GHz
- Burst immunity: ±2 kV
- Surge immunity: ±2 kV
- ESD: ±6 kV contact, ±8 kV air
Additional customer‑specific requirements may include:
- DB EMC06
- ÖBB/SBB requirements
- RIA12
The following applies to DC voltage:
Testing | basic standard | requirement | Limit value (measurement 3 m) | Limit value for industrial converters | Comment | Criterion Railway |
Interference emission | EN 55016-2-1 | 150 kHz bis 500 kHz 500 kHz bis 30 MHz | 99 dBµV 93 dBµV | 79 dBµV 73 dBµV |
|
|
Interference emission Housing | EN 55016-1-1 EN 55016-14 EN 55016-2-3 | 30 MHz bis 230 MHz 230 MHz bis 1 GHz 1 GHz bis 3 GHz 3 GHz bis 6 GHz | 40 dBµV 47 dBµV 56 dBµV 60 dBµV |
| 1-6 GHz measurement depending on the frequency of the transducer | A |
Burst | EN 61000-4-4 | ±2 kV 5/50 ns 5 kHz |
| 2 kV (criteria B) |
| A |
Surge | EN 61000-4-5 | 1,5/µs ± 2 kV. 42 Ω, 0,5 µF |
| 0,5 kV (criteria B) |
| B |
interference immunity | EN 50121-3-2 | 150 kHz – 80 MHz 10 V |
| 150 kHz – 80 MHz 10 V |
| A |
interference immunity | EN 61000-4-3 | 80 MHz bis 800 MHz 20 V/m 800 MHz bis 1000 MHz 20 V/m 1,4 GHz bis 2 GHz 10 V/m 2 GHz bis 2,7 GHz 5 V/m 5,1 GHz bis 6 GHz 3 V/m |
| 80 MHz – 1000 MHz 10 V/M 1,4 GHz -2GHz 3V/m 2 GHz -2,7GHz 1V/m
|
| A |
ESD | EN 6100-4-2 | ± 6 kV contact ± 8 kV air |
| ± 4 kV contact ± 8 kV air |
| B |
Conclusion
Due to the strict requirements of EN 50155 and related standards, DC/DC converters not specifically designed for railway applications are generally unsuitable for use in trains.
Beyond the standards, customer‑specific requirements—such as enhanced EMC, fire protection, or mechanical robustness—can render even certified devices unsuitable.
Bottom line: Choosing the right DC/DC converter for railway applications requires careful evaluation of standards, installation conditions, and customer‑specific requirements.
