Determining the source of electrical high-voltage transients to prevent light-rail car failure.The solution:
Combining the benefits of the field-programmable gate array (FPGA) and processor in NI CompactRIO hardware to create a rugged, semi-permanent monitoring system that records multiple data formats and rates, synchronizes the data and performs real-time analysis to remotely monitor sensors in an industrial environment for extended durations.
Governing subsystem interactions is a fundamental challenge for system integrators. Despite defining exhaustive I/O limits, sometimes failures occur, and it is not clear which subsystem interaction generated the destructive element. It is difficult to request subsystem vendor's resources to troubleshoot a problem that did not clearly originate from their equipment, and testing each system in isolation may not account for all interactions. In these cases, the system integrator may be best positioned to monitor the relevant parts of the overall system, isolate the problem source, and assign the appropriate resources to resolve the issue. The Siemens Rail Systems Division recently successfully performed this system integrator's task.
Over the past three years, one of our customers faced a recurring issue with our SD160 light-rail transit vehicles. Denver RTD, a bus and light-rail service operating in Denver, Colorado, has 170 Siemens vehicles in operation. These vehicles receive power from an overhead catenary system (OCS), which in turn receives power from RTD's power distribution network. The auxiliary power supplies (APS) on board each vehicle receive power from the OCS and condition it for use by most of the other onboard vehicle subsystems. This APS had a high failure rate, which caused a critical failure for the vehicle. The failure log reported a high-voltage transient on the power input to the APS, which led the vendor to believe that either Denver RTD or the onboard propulsion subsystem (which provides power to the APS during electro-dynamic braking) were providing power outside the acceptable transient limit. However, both RTD and the propulsion unit supplier confirmed that their systems should not generate such a transient. Each light-rail vehicle failure was extremely expensive and time-consuming for Siemens and our supplier, and the failures caused operating delays for our customer. We needed to monitor the situation, establish the root cause, and find a solution as quickly as possible.Preliminary diagnostic efforts
Initially, engineers at RTD verified OCS voltage levels met specifications. Subsequently, engineers from the APS vendor confirmed voltage transients that could contribute to the equipment failures, although when inducing these transients through various test routines, the APS always performed as designed. This testing required removing the vehicle from passenger service so personnel could monitor portable scopes. This method was inconclusive because high-voltage transients don’t occur very frequently and it is unlikely that a rare, damaging transient would occur during a short test period. It became clear that more comprehensive testing on vehicles in transit was needed to accurately characterize actual operating conditions.
The APS vendor built its own remote data logger to permanently install on an SD160 vehicle. It could obtain snapshots of system-level voltage data, but the data was insufficient to understand the surrounding environment and what was causing the transients. These approaches helped us realize that we needed to see the complete picture to diagnose the issue. We decided to build on these earlier efforts and design a rugged, remote system to monitor the trains for long periods of time to find and correct the problem.