CONTINUOUS analysis of the current drawn by 150 point motors at key locations near Amsterdam (right) has reduced train delays by more than 60% during trials, and ProRail has now approved a plan to install the equipment at over 1000 sites across the Dutch rail network.
POSS, which translates as Strukton Preventive Maintenance & Failure Diagnosis System, was first applied to 140 km/h points at Gasperdam Junction which have a crossing angle of 1:34·7. These are changed 80 to 90 times a day, and each switch has four separate motored drives including the moveable crossing. Strukton Systems Managing Director Sjoerd Jansen told the Rail-Tech 2003 congress in Utrecht on April 1 that the decision to develop condition monitoring for trackside equipment had been taken in 1998.
In addition to points, POSS is designed to monitor various kinds of lineside equipment such as track circuits and level crossing protection. The principle is that a parameter is selected which will indicate deteriorating performance before actual failure occurs.
In the case of points, the power drawn by the motor is measured by a current transformer, which is slipped over one of the wires feeding it. This meets a safety requirement that the control circuits must not be interfered with. A typical plot of motor current against time during normal operation is recorded by the POSS software, and if this changes shape significantly an alarm is given to the signaller and maintenance technician.
Communication is via the internet, using a GSM radio link from the equipment being monitored. Technicians arriving to check the installation can connect a laptop or use a mobile phone equipped with Bluetooth to interrogate POSS, and see the normal and actual current curves.
The shape of the current curve can also be checked before and after maintenance, and whenever a change or modification is made. For example, it is not unusual when points are tamped for distortion to increase the force required to operate the points, and POSS will immediately reveal this even though they still appear to the signaller to function correctly.
Strukton Systems, Netherlands
Reader Enquiry Number 148