Feature: Industrial electronics


Capacitors for railways require specialist technologies and designs


Mersen meets these challenges with its FTCAP capacitor units,


which consist of many single, internally-connected fi lm capacitors. T ey are designed with very low inductance, to allow for high switching frequencies. One special design allows optimal thermal transfer to a heat sink, which Mersen achieved by using specifi c materials and winding construction – to protect them from vibration, these units’ internal structure features single windings.


Highly vibration-resistant capacitors Vibration resistance is a very important factor in railway applications. To withstand them, fi lm capacitors can be optimised with solid soldered connections and casings made of stainless steel, aluminium or plastic, for fl exibility. Special winding constructions, contacts and mounting also exist for these capacitors – for example, by mounting through the case or directly on the case. T e toughness of these measures make FTCAP fi lm capacitors suitable for high G-forces, too, found in aerospace applications. In electrolytic capacitors, designing the internal structure with


solid welding of the contact lugs and special potting achieves extremely good resistance to vibrations. T e goal is to keep the winding stable in the cup even at very high oscillation frequencies, so pins in the cup’s cap and bottom hold the winding securely in place. Mersen developed its own cap technology, to ensure compliance


with quality standards in every case. In addition, the sealing technology was optimised by the company’s engineers and chemists, who also make custom electrolytes for special applications, for exact compliance with certain formulations. Mersen’s standard product range includes the GW series of


By Jens Heitmann, Account and Marketing Manager, FTCAP, Mersen


Credit: Stefano Lombardo for Unsplash R


ail vehicles, regardless the type – freight or passenger, electric motor coaches, urban, or underground and tram – require high-quality, robust components and systems adapted to harsh operating conditions like extreme temperatures, heavy loads and vibrations. Many of those


systems have capacitors, oſt en found in converters that manage the power – say, power for a tram AC network. DC link capacitors ensure constant voltage and deliver current


as needed, but need good thermal connection to heat sinks and a simple yet robust mechanical construction. T ey must also be vibration resistant, compact and easy to mount, and must meet specifi c requirements like ripple current capacity, voltage load, power loss and cost.


26 March 2023 www.electronicsworld.co.uk


aluminium electrolytic capacitors with a threaded connection. T ey are insensitive to high ripple currents, such as those on board power converters. As a side eff ect, however, the high currents also cause increased temperatures in the capacitors. For that, special winding constructions ensure optimal heat dissipation at the capacitor base. T e GW series is also available with optional base cooling by means of a Sil-Pad that dissipates the heat. T is makes the low-inductance GW series suitable for applications with high ripple currents in a temperature range from -40°C to 105°C. A long-time classic is Mersen’s S-series of FTCAP capacitors, which


are still regularly needed as replacements in railway applications. Mersen is one of the few remaining manufacturers that can fulfi ll orders for these products. T e special feature of the capacitors are their threads, which allow the capacitors to fi t into a threaded hole on a mounting plate. Although passive electrical components are now generally soldered onto the PCB, this threaded connection is perfect for large aluminium electrolytic capacitors for high current loads. Not least of all, the Mersen Energy Cap series is used in railway


technology as DC link capacitors. Film capacitors’ special feature is they can have diff erent height terminals, which facilitates solid mounting on laminated busbars. T is enables operation at consistently high reliability – also because it eliminates the need for compensating spacers, which oſt en add contact resistance because they are made of diff erent materials. Another advantage is that the same screws can be used for both terminals, since they have the same thread depth.


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