Can rail operation disturbances be detected before they even occur?
Tramways, long-distance trains, and freight trains need safe drive systems and reliable electric storage systems to run smoothly and without disruptions. Faults must be recognised and eliminated as early as possible to ensure high availability in rail traffic.
What is the advantage of trains running on unearthed power-supply systems?
In most cases the electric loads in rail vehicles should not be switched off. For this reason, frequently unearthed electrical circuits (IT systems) are used in these vehicles. In the case of insulation faults these power circuits allow operation to continue, since the first fault usually does not result in a dangerously high current as there is no connection to earth. Instead of triggering a circuit breaker (and hence a corresponding power outage) an alarm is given. The necessary maintenance can be planned for as soon as possible before this disturbance will cause other problems. At the same time the rail vehicle continues to run.
A second fault in the same system, however, changes the situation, for then the fault current can be so high that it might cause damage or pose a fire hazard. Recognising and eliminating the first fault quickly while the system is still operating is therefore crucial.
Apart from the rail sector, also other key areas such as medical or industrial equipment use unearthed systems in all those cases where unplanned shutdowns or outages can endanger safety or lead to contractual penalties or image loss.
Overview:When are unearthed systems (IT systems) useful?Unearthed systems (IT systems) are employed especially in equipment where 100% availability is crucial. This applies, e. g., to operating theatres or to manufacturing plants in the chemical industry, where equipment downtimes pose a great danger to human life or health or can cause enormous financial damage. In an IT system all active conductors are insulated from earth. Hence, in the case of a body contact or an earth-leakage fault the leakage current is low. Due to this low fault current, a first insulation fault need not and will not result in a system shutdown. Comparison to earthed systems (TN systems)In an earthed system (TN system) one or more points of a network or of electrically operated equipment are connected to earth to ensure electrical safety. When a leakage current that is too high occurs, the power supply is disconnected, and hence the equipment is shut down to protect people and machinery. |
How does insulation monitoring in the rail system work?
Sustainable drive systems of rail vehicles but also a more extensive rail infrastructure make electric networks even more complex and susceptible to disturbances. Real-time information on their condition permits recognising and eliminating possible dangers as fast as possible. One solution employed here is continuous monitoring by an insulation monitoring device (IMD). This device can detect critical values and indicate imminent problems even before an alarm is given. In this manner the system's condition can be monitored in real time, and corrective measures can be taken before faults can have a critical effect. As a consequence, unplanned downtimes are reduced, and system availability is high.
Keeping unearthed systems operative after an insulation fault requires an extensive search for the fault's location and root cause. Here insulation fault location systems (IFLS) that enable locating technical faults during ongoing operation and without interruption of the power supply come in. In trains equipped with an IFLS, locating of a fault can start immediately after its occurrence.
Summary
Especially for rail vehicles with their high operational requirements one can say: There is hardly an electrical power-supply system that will remain unaffected by faults in the long run. An effective system for detecting and locating faults is the best solution to ensure fewer downtimes and uninterrupted availability of essential systems.
