# Research on Interference Mechanism of 25 Hz Phase Sensitive Track Equipment from Unbalanced Current
## 1 Introduction  
With the development of electrified railways, scholars in many countries have gradually attached importance to research on track circuit disturbance caused by the traction return system. At present, the railway traction return system adopted in France includes rails, chokes, grounding wires, grounding electrodes, protection wires and equipotential bonding wires between conductors. However, the channel of the signal circuit is not the rail, and the through ground wire is used as the return wire in parallel with the rail [1]. The railway traction return system adopted in Germany consists of rail, return line, catenary, equipotential bonding line between conductors, grounding terminal, etc. [2]. The rail circuit is a circuit composed of rail as the transmission medium, electrically isolated at both ends, and connected with the power transmission and receiving equipment [3]. At present, nearly 98% of stations on electrified railways use 25 Hz phase-sensitive track circuits [4]. The unbalanced current generated by unbalanced factors such as track imbalance and adjacent rail interference in the track circuit will invade the equipment. When the rail unbalanced current is too large, it will cause interference to the equipment, which is likely to cause the circuit to flash red and other misoperations, leading to emergency braking of the train, affecting traffic safety [5]. Therefore, it is necessary to study the unbalanced current in the 25 Hz phase-sensitive track circuit. The research is of great significance to the analysis of equipment malfunction in the track circuit. Aiming at the problem of the unbalanced current of the track circuit, [PERSON] pointed out from the view of signal maintenance that the causes of the unbalanced traction current of two rails mainly include the reasons of the signal equipment itself, the improper position of the tower ground wire on the rail on one side of the track circuit and suction line [6]. Yet, he did not analyze the internal mechanism of the unbalanced current and the interference mechanism of the choke transformer, relay and other equipment from a theoretical point of view. [PERSON] explained the traction return current distribution model in three ways: direct power supply, current absorption transformer power supply and autotransformer power supply. He introduced the causes of the unbalanced current but did not consider the unbalanced current caused by hanging the grounding wire, and did not analyze the impact of unbalanced current in detail [7]. [PERSON] and [PERSON] pointed out that the unbalanced impedance of the rail will lead to the generation of unbalanced current, and it will interfere with the choke transformer and signal equipment [8; 9]. However, they did not explain the interference caused by adjacent tracks of the 25 Hz track circuit and did not consider the effect on the coils of the operating device. Based on the theory of rail transit line impedance and admittance, [PERSON] et al. obtained the self impedance and mutual impedance of the track under power frequency, but they did not further study the influence of impedance on the traction return current [10]. [PERSON] et al. pointed out that the impedance of the two rails cannot be completely equal in actual engineering. Unbalanced traction return will occur between the rails. The unbalanced current of the rails will cause the impedance of the choke transformer to increase, where the signal flow path is the rail. The unbalanced current in the rail will cause interference to the track circuit, and even damage the signaling equipment [11]. In view of the influence of the unbalanced current on track circuit equipment such as the choke transformer and binary two-bit relay, [PERSON], combined with the red ribbon fault, pointed out that the process of adding the ground wire to power outage equipment will change the traction return current and affect the rail current distribution and track circuit [12].