Quick Dips

Guarding the Line

A new fault monitoring system on the North Island's Main Trunk Line has substantially reduced the time taken to locate and repair faults. The system means better train management and has earned the company involved, Otari Electronics, a finalist placing in ECNZ's Rutherford Awards.

Due to the high voltage running through the overhead power supply of the Main Trunk Line, and the harsh environment through which the track runs, the system is vulnerable to failures. When it was necessary to search 30 kilometres of track for the cause, often at night and in bad weather, the time taken to locate and rectify a fault could be uncomfortably long.

Otari devised a solution to this problem with a fault location device, a specialised "system control and data acquisition system" which monitors the whole electrified section of track looking for fault conditions.

At each electricity feedpoint, a microprocessor device called a Fault Detection Unit, or FDU, continuously monitors current. When a fault occurs, the FDU records the wave form and statistics about the fault, including time and date. Using unique fault detection logic, system fault currents which have a lower magnitude than the current drawn by a heavily-loaded locomotive can also be detected.

When a failure occurs, the system operator based in Palmerston North is able to speedily find the location by dialing up each FDU, using the standard telephone system. The fault detection system can then give the site of the problem, often to within 200 metres, by the use of the in-built "auto-locate" function. The operator can despatch repair teams to the fault site, confident of the location.

Typical faults experienced have included shorted lines due to branches of trees, bark, air-borne salt and other materials carried by the wind, and fauna such as birds and possums. Other problems have included road accidents and the lining materials inside tunnels becoming dislodged.