Track circuits are used as train detection system on the railway infrastructure. At the border of a track section, a transmitter injects an electrical signal with a defined frequency and amplitude into the rails. This signals can be captured and analysed by the receiver at the other end of the track section. If there is no train on the corresponding track section, the signal can be detected by the receiver and the track section is reported as 'clear'.
With a train on the track section, the signal is short-circuited by the axles of the train and can no longer be detected by the receiver. The track section is then reported as occupied.
Low frequencies in the range from 0 Hz to 500 Hz are used for track circuits with electromechanical receivers. Examples of track circuit operating frequencies are of 42 Hz, 50 Hz and 100 Hz.
Modern rail vehicles with a three-phase drive use static power converters to adjust the traction current to the required frequency and amplitude. The switching of semiconductors in power converters leads the higher frequency harmonics in the line current. If these harmonic frequencies fall into the sensitive band of the track circuits, this could lead to a dangerous malfunction of the receiver.
To prevent such dangerous failures, the infrastructure manager has to determine the maximum permitted interference current in the relevant frequency bands. The train manufacturer has to demonstrate compliance with these limits for all normal operating conditions and for selected or all failure modes. This is pre-requisite for the safety acceptance of new trains.
ENOTRAC has developed the Interference Current Monitor (ICM) as a protection device in collaboration with Telma AG. The ICM constantly monitors the primary current of the railway vehicle. If parasitic currents exceed the limits for a pre-defined time, the ICM will open a relay contact, which can be used to open the main circuit breaker or to stop the converter.
The current is measured with a compensated hall-effect transducer equipped with a test winding, which enables the ICM to constantly verify the correct function of the transducer. The ICM can monitor up to two frequency bands simultaneously.
The installation of the ICM on the traction vehicle facilitates the formal demonstration of the compatibility of the vehicle with the track circuits. The safety integrity of the ICM was analysed and demonstrated with FMEA and quantitative fault tree analysis.
To meet the requirements for electronic devices on railway vehicles, the ICM had to undergo extensive type tests, including:
|Compliance with EN 50155||Temperature class:||T3|
||Interruption of the supply voltage:||S2|
|Environmental simulations according to EN 61373:||category 1, class B||
|EMC tests according to EN 50121-3-2||Fast transients (Burst):||Criterion A|
||Withstanding voltage (Surge):||Criterion B|
||Electromagnetic HF-field:||Criterion A|
|Fire resistance according to EN 45545||
ENOTRAC AG, Seefeldstrasse 8, 3600 Thun, Switzerland, Tel: +41 33 346 66 11, Fax +41 33 346 66 12
ENOTRAC SA, Avenue de la Gare 1, 1003 Lausanne, Switzerland, Tel: +41 33 346 66 19, Fax +41 33 346 66 12
ENOTRAC UK Ltd, Chancery House St Nicholas Way Sutton, Surrey SM1 1JB England, Tel: +44 20 8770 3501