The interference of electric traction on the track circuit transmission system is not the power supply system, but mainly the influence of power fluctuation, rectifier commutation, large load change, train starting or braking, power supply arm switching, vehicle inverter [1] during train operation. Whether the train will generate a large number of electromagnetic interference signals to the signal transmission system during operation, thereby causing the track circuit "red light band", or even causing the "insulation joint" of the turnout section to burn out, is a concern of the signal industry and also a concern of on-site maintenance. This paper analyzes whether the electromagnetic interference signals generated during train operation will affect the track circuit, on-board signal, and vehicle-to-ground communication (TWC) of the signal system through on-site testing. 1 Relationship between train operation process and traction voltage and current changes Through dynamic online monitoring, when only one test train is running on the entire line, the traction voltage and current change significantly with the train operation status. The actual monitoring data shows that 1500V "DC" is far from the ideal 24 pulse wave. The test results are shown in Figure 1. As can be seen from Figure 1, the maximum value of the DC voltage of the contact network is about 1800V and the minimum value is about 1500V, so the fluctuation of the contact network is about 20%. During the time period A1→B1 and A2→B2 when the train is requesting power from the contact network, the voltage drop of the DC voltage of the contact network exceeds 200V. During the time period B1→C1 and B2→C2 when the DC current of the contact network remains constant, the DC voltage of the contact network also remains constant. During the time period C1→D1 when the train gradually stops requesting power from the contact network, the DC voltage of the contact network gradually increases. When the train stops requesting power from the contact network, the DC voltage of the contact network is basically maintained at about 1700V. During the braking process of the train, the maximum inverter feedback voltage amplitude of the vehicle is about 150V; during the parking period, the grid voltage caused by the inverter fluctuates by about 50V, which is consistent with the pulsation coefficient of about 50V of the 12-phase 24-wave full-wave rectifier [2]. 2 Analysis of interference to track circuits As the train runs, the interference waveforms within the working range of the audio track circuit are measured as shown in Figure 2. The top horizontal line in the figure indicates that the interference limit within the normal operating range of the audio track circuit is 600mA[3]; A1, B1, C1, A2, B2, and C2 respectively mark the special points of the interference signal change. As can be seen from Figure 2, during the time period A1→B1 and A2→B2 when the train is requesting power from the contact network, the amplitude of the interference signal within the operating range of the audio track circuit increases continuously as the DC current of the contact network increases; during the time period C1→A2 when the train stops requesting power from the contact network, the interference signal still has a certain amplitude, which may be the interference caused by the start and stop of the air conditioning unit on the train. Analysis of all the measured data shows that within the operating range of the audio track circuit, the maximum value of the interference signal amplitude is 300mA and the minimum value is 0, which does not exceed the limit. 3 Analysis of the interference of the onboard signal As the train runs, the interference waveform within the operating range of the onboard signal is shown in Figure 3. The top horizontal line in the figure indicates the interference limit within the normal operating range of the onboard signal (1000mA)[3]. As shown in the figure, the maximum amplitude of the interference signal within the normal operating range of the onboard signal is 500mA, which does not exceed the limit. 4 Analysis of interference with vehicle-to-ground communication The interference waveforms within the operating range of the vehicle-to-ground communication signal recorded during vehicle operation are shown in Figure 4. The top horizontal line in the figure represents the limit of interference within the normal operating range of the vehicle-to-ground communication (TWC) signal (216mA[3]); A1, B1, A2, and B2 respectively mark the special points of interference signal change. As shown in Figure 4, during the time periods A1→B1 and A2→B2 when the train requests power from the contact network, the interference waveform of the vehicle-to-ground communication signal and the DC current of the contact network are related, but the interference waveform will have signal distortion at some points. After analyzing all the recorded data, it can be seen that the maximum amplitude of the interference signal within the normal operating range of the vehicle-to-ground communication signal is 125mA, and the minimum value is 0, which does not exceed the limit. 5 Conclusion Through actual monitoring of train operation, it can be seen that the traction voltage and current change significantly with the train operation status. The harmonic components they generate randomly interfere with the frequency band of the subway signaling system. However, analysis of the measured data shows that the electromagnetic interference generated during train operation is within the normal range, and has minimal impact on the track circuits, on-board signals, and train-to-ground communication signals of the signaling system. Research on electromagnetic interference from trains to signaling systems is still a relatively new topic in China. Although limitations prevented testing of electromagnetic interference from trains to the signaling system under normal operating conditions during the testing process, the test methods and results have laid a foundation for further research on this issue and provide valuable reference for future equipment construction and maintenance.