Applications of safety transient voltage suppressors in the track circuits of railway signaling systems

This research presented the utilization of Safety Transient Voltage Suppressors (STVS) in the track circuits of railway signaling systems, occurring during circuit switching due to changes in track occupancy conditions, resulting in damage and malfunction of the BR966F2 relay. The study employed Failure Modes and Effect Analysis (FMEA) combined with 1kV actual transient overvoltage testing featuring a waveform slope of 184/380 μs. Results revealed two transient voltage suppression levels encompassing Set A_(a,b), Set B_(a) and Set C_(a,b) as well as Set A//Set B//Set C and All Mode. These configurations achieved a clamping voltage of 41.6 V, categorized as Stage 1. Configurations like Set A_(c), Set B_(b,c) and Set C_(c) displayed increased series circuit behavior leading to a clamping voltage of 48.6 V, categorized as Stage 2. The application of STVS device in the track circuit of the signaling system reduced the transient voltage by diversion of the Transient Current or ISTVS through the STVS device into the ground system or the clamping voltage at the STVS device. This prevented the transient power from flowing into and damaging the relays of the track circuit, leaving only the clamping voltage with a missing peak wave. This contributed to the stability of the track circuit within the railway signaling system while also raising the Safety Integrity Level (SIL) to a higher standard, in accordance with the specifications of IEC 16508-4 and the unique requirements of the State Railway of Thailand. These enhancements increased the advanced safety system within the track circuit, particularly for train control and train operation functions of the State Railway of Thailand