Development and performance analysis of a novel impedance bond for railway track circuits

The ZPW-2000 track circuit is the dominant track circuit system used in China. On standard plain line track it is used as a jointless track circuit where `tuned zones´ are used to separate adjacent tracks operating at different frequencies. Owing to the complexities of station layouts it is not possible to use the ZPW-2000 as a jointless track circuit within stations, so a solution incorporating mechanical joints is commonly used. The station environment is known to have high levels of electromagnetic interference, and such environments can cause interference in the track circuit resulting in signal degradation and failure. An integrated solution that allows the ZPW-2000 track circuit to be used dependably in jointed operation that is able to cope with the electromagnetic environment found in stations is therefore required. In this study, a solution based on impedance bonds is developed to alleviate interference problems with the ZPW-2000 in harsh electromagnetic environments. The study presents an innovative design of impedance bond incorporating an air gap transformer and a double function filter circuit. The impedance bond was found to have an impedance of below 0.01 Ω at the resonant frequency of 50 Hz, and in excess of 17 Ω at other signal frequencies. The impedance bond is shown to eliminate interference while meeting the requirements of signal transmission on rail tracks. In this study, both theoretical analysis and the results of laboratory tests are presented.