Soft magnetic low-loss iron powder chokes developed for railway applications

September 3, 2013

September 3, 2013

SMP Sintermetalle Prometheus GmbH & Co KG (SMP) based in Graben-Neudorf near Karlsruhe, Germany, has been producing soft magnetic composite (SMC) components from iron and iron-powder alloys for over thirty years. SMP’s product range includes low-loss inductive custom components based on in-house-developed powder composites, such as filter, commutating, step-up converter, power recovery and single-conductor chokes.


SMP Sintermetalle Prometheus GmbH has developed

a range of low-loss iron powder chokes for railway


SMP’s inductive components can be produced for frequencies of up to 200 kHz and currents of up to 1000 amperes. Their sizes range from 36 mm to 300 mm diameter and their weight from 50 g to 130 kg.

The company recently announced the development of a range of low-loss SMC chokes for use in railway technology. The company states that the task of the chokes is to limit not only the input current on the primary side, but also the output current on the secondary side in the inverters used for three-phase asynchronous motors and on-board units.

In order to minimise losses in the inductive components, SMP uses core material of iron powder composites developed specifically for these applications. Besides their low loss characteristics, the components for use in rail vehicles must fulfil a number of other demanding requirements: they must be resistant to vibration and impacts as well as to high temperatures, they must fit into small spaces, and they must be completely impenetrable by dust, dirt and water. The chokes produced by SMP for use in motors in passenger coaches are made from a magnetostriction-free material developed specially for this purpose, which makes them very quiet.

Inductive components produced by SMP are said to be able to sustain voltage rise rates of up to 10 kV/µs. After installation in the inverters, they undergo rigorous shake tests to ensure that they are resistant to impacts and vibration in all directions. In order to withstand the high temperatures that prevail in railway applications, all chokes from SMP are constructed in compliance with the UL-listed Class H insulation system, which provides thermal protection up to 180°C.

A protective paint coating according to IP66 protects them from dust and water and enables them to be fitted outside the inverters. The advantage of this kind of installation is that the heat generated by the choke is discharged outside the inverter, so fans are not needed to dissipate the heat. Another advantage is that the inverter can then be designed with considerably smaller dimensions. The choke can also be adapted to the substantially lower ambient temperatures in underfloor-mounted electronics. To simplify mounting outside the inverters, SMP produces the chokes with special mounting fixtures.

Besides railway engineering, SMP states that SMC inductive components are used in inverters for industrial applications, in wind turbines, in photovoltaic inverters, in medical engineering and many other drive and power electronics applications. In order to cover the entire component production cycle, SMP established an in-house iron powder production plant in 2008.  

September 3, 2013

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