Electronic Design

Low-Loss Chokes Serve Inverters In Railway Applications

Components for use in rail vehicles must fulfill strict requirements. They must be vibration- and impact-resistant; withstand high temperatures; fit into small spaces; resist ingress of dust, dirt, and water; and, when used in passenger coaches, operate with no or little noise. A range of chokes designed just for these applications fits the bill. Such chokes for inverters limit the input current on the primary side. To minimize the losses within its chokes, SMP Sintermetalle Prometheus uses cores made from proprietary powder composites.

Chokes for rail vehicles must be vibration-resistant and impact-resistant in all directions. To ensure that they fulfill this requirement, they are subjected to rigorous shake tests after being installed in the inverter. They must also have a high rate of voltage rise of up to 10 kV/µs. Because of the high temperatures that occur in railway applications, they must have high thermal stability as well. This is achieved with a UL-listed Class H insulation system, which provides thermal protection up to 180°C.

A further requirement for rail-vehicle components is coating with a protective paint that resists dust and water. Because these chokes can be installed outside the inverters, the heat generated by the choke is not discharged inside the inverter. As a result, the inverters stay cooler without the need for fans, saving both power and space. Placing the choke outside the inverter also reduces the inverter’s overall dimensions, which further cuts space and energy demand.

External mounting allows the chokes to be designed for lower ambient temperatures. While inverters in railway applications can have an internal temperature of 70°C to 80°C, the outside temperature to which underfloor-mounted electronics are exposed is unlikely to exceed about 40°C. To simplify mounting outside the inverters, SMP provides the chokes with special mounting fixtures. The choke and the mounting plate are installed on the outside of the device. The connecting cables pass through a sealed opening.

For use in drive control, power electronics, power generation, wind power and photovoltaic installation as well as instrumentation and control, SMP supplies chokes and filters for frequencies up to 200 kHz and current ratings up to 1 kA. Depending on their application, the inductive components are constructed either as single-conductor chokes for high-current applications, individual chokes, choke modules, or LC filters. These components offer a high energy storage capacity at low volume, reduced losses, good electromagnetic compatibility (EMC) characteristics, and a cost-conscious design.

SMP Sintermetalle Prometheus GmbH & Co KG


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