London Underground - Runback Protection

Application: Runback Protection Systems
Installation Area: London Underground
Client: Metronet BCV / Metronet SSL

SELLA CONTROLS had already developed a programmable control unit for railway applications, with the most common use for this design being the provision of throttle control, standstill detection and speed monitoring and limiting.

Subsequently we were approached by Metronet to provide a safety solution which would prevent trains from rolling backwards once they had reached a destination. Function and operation is primarily determined by the programming of the two RISC controllers and thus a high degree of redundancy and self checking can be built in.

Our design met the requirements of SIL2 according to IEC 61508. The design hosts 8 digital inputs, 1 dual channel sensor input, 5 relay outputs, 1 pulse output and an RS232 port. The system also incorporates a 2 x 16 display for fault diagnosis and status information. Upon detecting a fault, the system will fail to the safe condition.

The runback system also incorporates a data logging facility to record when faults and runback conditions occur. A custom designed sensor is used on some of the trains and is fitted to the end of the axle or traction motor.

Runback protection equipment is fitted to trains on the following lines:

  • Bakerloo
  • Circle
  • District
  • Hammersmith and City
  • Metropolitan
  • Waterloo and City


Please contact us for further information

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