A novel protection scheme for DC electrical railway systems using high-frequency signal injection

A new protection scheme for DC electrical traction supply systems is introduced in this paper. The method is based on continuous measurement of the high-frequency impedance of the electric supply system. The high-frequency impedance of traction supplies is shown to be correlated to the physical integrity of the system. The measurement is synthesized by injecting the high frequency signal in the line and blocking the measurement signal from low-impedance paths, such as the train and substations. Using this injection and blocking technique, a new high-frequency system, which is sensitive to leakage currents, is created. The proposed method can be used for both protection and monitoring of the physical condition of the system. The method is non-intrusive, non-destructive, and can be used for both DC and AC systems without making major changes to the existing system, or incurring large costs. The proposed high-frequency based electrical railway monitoring system is analyzed, simulated, built, and experimentally verified.