Railway Capacitors

Cambridge Capacitors have supplied a variety of capacitors for use in Railway Signalling applications.  Adjustable capacitors are generally used where there is DC traction and AC signalling system in the 25 to 150Hz frequency range.

One or more adjustable capacitors are fitted in each track circuit and switches are used to adjust the capacitor to match the requirements of the individual conditions.   (Eg. Length of track and conductivity of the track ballast.)  The circuit is thereby tuned to operate a vane relay and change the appropriate signal, in the presence or absence of a train.

These capacitors are approved by, and have been supplied for many years, to Network Rail, London Underground, Strathclyde PTE, Tyne and Wear Metro and the Docklands Light Railway.

A new, fully approved design has been introduced for installation with the latest Mk3 track circuit bonds and these are available as a 5 to 15 µF capacitor, adjustable in 0.33µF steps. This is now the preferred product for the UK rail network. Previous standard values used were 3 to 12.3µF (adjustable in 0.3 µF steps) and 1 to 20 µF (1 µF steps) and these are still available for the replacement market.  Cambridge Capacitors have also supplied a 30 to 60 µF (1 µF steps), which was specifically commissioned, designed and manufactured by Cambridge Capacitors for use with the Channel Tunnel Rail Link line.

All adjustable capacitors are housed in plastic cases.

These capacitors are manufactured using high quality, low loss, metallised polypropylene, in a fully encapsulated dry construction. (No risk of liquid leakage.)  They are designed and manufactured for a minimum life expectancy of 25 years.

NEW PRODUCT - TRACK CIRCUIT TUNING UNIT

Close tolerance fixed capacitors are also available for signalling circuits operating in the frequency range 4 kHz to 6 kHz and Cambridge Capacitors have a unique range of products that have less than 1% capacitance drift over the temperature range -40 to +70C. This product has been specifically designed to replace polycarbonate capacitors that are no longer available.

See also Cambridge Capacitors "Custom Designed" information.