A Novel High Frequency Impedance Analysis Method to Protect DC Electrical Railway Systems

In this article, a new protection scheme for dc electrical traction supply systems is introduced. The method is based on a continuous high-frequency impedance measurement of the electric supply system. The measurement is synthesized by injecting a high-frequency signal into 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 correlation between the traction supplies' high-frequency impedance and the physical integrity of the system is shown. The proposed method can be used for both protection and monitoring of the physical condition of the system. The method is nonintrusive, nondestructive, 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.