Safety Measurements in Distributed Power Systems in Railway Applications
The Transient Recorders and Measurement Satellites of AMOtronics’s SATURN series offer a proven solution for complex measurement tasks in distributed power systems having differing reference voltage potential. The technique is used during e.g. homologation testing of railway vehicles. The goal: Find frequencies in the vehicle’s return current that can disrupt train detection systems by signal interferences or overlays.
The train is one of the safest means of transportation. This is also ensured by fully automated safety features such as train detection. These safety systems continuously check whether a vehicle is on the track and warn if the route is not free. The rails are as well used as transportation media for communication as for conducting the return current of electrically supplied trains. The power electronics of modern locomotives could unintentionally disturb the communication systems by signal interference and overlapping. Therefore each type of vehicle has to pass interference current tests before qualification. These tests ensure that the multiple mega watt drives operate outside the critical frequency ranges.
The noise-sensitive measurements are even more challenging when multiple locomotives are coupled together to form a train. The current must then be measured in parallel in several vehicles. Differences in voltage potential of several hundred volts can be found between the measuring points, so that there is no unique reference potential available. In such so-called “multiple tractions” AMOtronics’s SATURN series high-speed measurement technique allows highly synchronous measurements on distributed parts with one single system.
Fiber optic cables withstand surge currents
This is made possible by use of so-called Measuring Satellites. Via fiber-optic cables digitized measurement signals are transmitted purely optically to the recording and evaluation device - the Transient Recorder. Unlike conventional electric data lines, the fiber optic cables are immune to electromagnetic distortion.
Also transient distortions, which are typical for railway operation and which can arise for instance at the point of contact between pantograph and catenary, do not influence the measurement signals. Thus, distributed quality tests can be performed with a central measurement system while maintaining best possible synchronicity and precision of the data in the presence of strong interfering fields.
Due to these advantages the AMOtronics system is suitable for these kinds of tests and is used by the engineers at Roerden GmbH, a test body recognized by the German Federal Railway Authority for inspection of rail vehicles in Germany.
During the test runs the current is measured simultaneously in the different traction vehicles by means of so-called Rogowski coils. The coils are connected directly to the AMOtronics measurement Satellites and are powered and monitored for failsafe operation by the Satellite power control system. At a transmission rate of 2 GBit/s the data is optically transmitted from the measurement heads to the central recording system. The different cable lengths in the up to 200 meters long coupled trains have no influence. The integrated software of the SATURN Transient Recorders automatically determines the optical signal propagation time to each measurement Satellite and compensates for it. Theoretically almost any distance can be bridged while maintaining the synchronicity of all measurement channels.
Summary
The reliability of the measurement technology is crucial for the work of the test body in Dortmund. Only reliable measurements and data allow it to prove with certainty that the train’s power electronics do not cause critical frequencies. In addition to numerous other applications in the power generation and transmission this makes the high-speed measurement technology of AMOtronics a significant contribution to railway safety.
Example of a SATURN Transient Recorder for safety measurements e.g. in railway vehicles
