DIN-rail power supplies for railway applications

  • March 24, 2017
  • PULS Pte Ltd
  • News

By Christoph Frodl, Special Applications Engineer at PULS 

Train travellers and commuters want one thing above all else from the railway: Reliability. This expectation is also passed on by the railway company to its suppliers, right through to the manufacturers of individual components, such as power supply units.

Power supply manufacturer PULS has been intensively involved with the requirements arising from railway applications in terms of reliability, and has identified many other parallels with the industrial environment: Efficiency, size, availability, service life duration and resistance to EMC and ambient conditions are equally important for power supplies in all application areas. Based on its decades of experience in developing and manufacturing large scale industrial power supplies, the company has developed a range of products specifically designed for railway users: the DIN-RAILway range. The product range includes 1-phase and 3-phase devices (power range: 240W and 480W) as well as DC/DC converters (power range: 100W, 200W and 400W), for DIN-rail mounting. This makes the high technology standards of the industry and the intuitive assembly mechanism available to railway users.

High demands of the railway

The requirements in the rail sector are high: Even in the case of high mechanical shock loads, no failures are permitted to occur in a greatly extended temperature range. Mechanical fans are not generally permitted as these represent an increased source of error. This in turn requires the highest levels of efficiency for highly compact devices that dissipate their heat loss via natural convection.

All these requirements are regulated in the railway sector by the EN50155 standard, which applies to the use of electrical equipment on rail-going vehicles. Proof of compliance with EN50155 must be provided via testing.

The power supplies in the PULS DIN-RAILway range have successfully passed the following tests:

  • Vibration resistance (DIN EN61373):This standard represents much tougher test conditions than is required for industrial power supplies. Thanks to the built-in spring-clamp terminals and the conformal coated PCBs, the devices are extremely resistant to impact and environmental influences. This means they can be installed in the vehicle body, including on the roof and in the underfloor area.
  • Temperature range:Industrial power supplies from PULS are operated without derating up to an ambient temperature of +60 °C. For the railway sector, suitability according to EN 50155 for the extended temperature range up to 70 °C and 85 °C for 10 minutes was successfully proven for the units.
  • EMC resistance (EN50121-3-2):In the railway sector, high demands are placed on voltage strength and immunity to interference. The low-noise circuit layout in the units provide high EMC resistance here.
  • Fire protection according to EN45545-2:Industrial power supplies from PULS are UL-certified as standard and have already been tested in accordance with the new fire protection standard. The units are not cast, meaning they have a low fire load and are also extremely lightweight.

Technical modifications to the circuit design were primarily necessary in terms of the input voltage range, which differs from industry requirements. 110VDC is supported with the tolerances ± 30% static and ± 40% for 100ms. The same applies to the typical alternating voltages in railway technology.

Thanks to the successful EN50155 certification and the modified circuit layout, the DIN rail power supplies can be used in the train and on the line. Typical application areas include the central power supply, air conditioning technology, train communications, infotainment, signalling and train safety.

High efficiency and huge power density

In the industrial field, the best power supplies feature properties such as maximum efficiency, minimum dimensions, lowest weight, longest service life and maximum availability.

These properties are of course also of particular interest in the railway sector. To give an example: The CPS20.241-60 unit from PULS has an output power of 400W across the entire temperature range, has an integrated MOSFET decoupling circuit on the output for redundant operation with passive load distribution and an efficiency of 94%. In the event of a failure in the input voltage – even in the event of a short circuit – the output voltage is still available for more than 20ms. Short interruptions can easily be bridged as a result. This enormous power density is achieved with a housing width of only 65mm and a weight of 1,000g. What is increasingly appreciated is the active inrush current limiter and the integrated polarity protection for DC voltages at the input.

Assembly onto the DIN-rail

The most noticeable outward deviation of current power supplies for rail applications is of course the mounting mechanism for the DIN-rail. In conventional wall mounting in trains, the heat dissipation is often provided via a mounting plate. These concepts are only used in industry in exceptional cases. The majority of electronic and electromechanical devices are mounted on DIN-rails. The industrial concept of PULS therefore also offers significant advantages in the railway sector, as vibration-proof mounting on a DIN-rail is only possible if the devices have a high-quality DIN-rail mount and minimum dead weight; the latter in turn requires devices with very high efficiency levels.

It is not only the rapid assembly onto a DIN-rail that is an advantage, but also the completely vibration-free connection via spring-clamp terminals. Loose screw connections are one of the most common causes of electrical system failures and frequently result in fires. In industry, spring-clamp terminals have largely replaced screw connections, from the signal range to the power range, as the vibration safety is automatic in the case of spring-clamp terminals.

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