# Research on Interference Mechanism of 25 Hz Phase Sensitive Track Equipment from Unbalanced Current
## 4 Analysis of Track Circuit Misoperation Test
### Analysis of Unbalanced Current Simulation Test  
This paper simulates the unbalanced current of one sending and one receiving section for the test. In order to simulate the state of the flash red ribbon in the field, it is necessary to inject 50 Hz unbalanced component into the 25 Hz operating waveform at the receiving end. In this experiment, a 50 Hz voltage source is used as the excitation source of the unbalanced current. The circuit schematic is shown in Figure 15; the secondary side of the isolation transformer is connected in series with the 2 terminals of the receiving-end choke transformer, and the primary side of the isolation transformer is connected to the voltage regulator to adjust the 50 Hz unbalanced current in the 25 Hz track circuit. In order to analyze the collected waveform reliably, it is necessary to slowly increase the output voltage of the voltage regulator. In this process, collect and observe the change of 50 Hz unbalanced current of the receiving circuit until the binary two-bit relay or track relay acts,  
Figure 14: Relay core loss. Figure 13: Relay coil flux density. then stop increasing the voltage. Record the unbalanced current value, voltage, current and other electrical quantities of the track circuit. Voltage probes are arranged at terminals 1 and 3, 2 and 3, 4 and 5 of the choke transformer, respectively, and current probes are arranged at terminals 1 and 4. The current probe is arranged at the local coil and track coil side of the binary two-bit relay. When the unbalanced current is not connected, the operating state waveform of the choke transformer is shown in Figure 16. It can be seen that the voltage and current frequencies of the primary and secondary sides are 25 Hz, without 50 Hz voltage and current interference. However, due to the influence of track imbalance and other factors in practice, the effective value of terminal 1 of the primary side current of the track transformer is 2.9 A, the effective value of terminal 3 of the primary side current of the choke transformer is 12.5 A, and the effective value of the secondary side terminal current of the choke transformer is 98 mA. Therefore, the unbalanced current is also generated in the track circuit, and the value is 9 A.  
Figure 16: Choke transformer waveform without interference. Figure 15: Unbalanced current simulation test circuit. Figure 17a,b show the waveforms of the receiving end choke transformer during the simulation of the interference and the misoperation. It can be observed that the voltage and current of the primary and secondary sides of the choke transformer are disturbed by the unbalanced current. With the injection of 50 Hz interference voltage and current into the 25 Hz normal operating waveform, it can be found that the 25 Hz secondary terminal current waveform of the choke transformer is distorted. The effective values of the current on both sides of the track are 11 A and 27 A, respectively. It can be calculated that the unbalanced current in the track circuit reaches 16 A, and the choke transformer gradually enters a saturation state. It can be seen from Figure 17b that the current on both sides is 11 A and 37 A, respectively, and the unbalanced current value reaches 26 A. The choke transformer is already in a severe saturation state. Figure 18a,b shows the waveforms of the relay during the interference and the misoperation. It can be found that the terminal voltage of the track coil changes significantly, and some waveforms of the indoor relay are also affected when the interference source is injected. As shown in Figure 18a, the effective value of the track coil side voltage of the binary two-bit relay decreases from 22 V to 15 V. According to the release value of JRJC1-70/240 not being less than 8.6 V, the reliable drop value is 7.74 V; it can be seen that the relay operation standard is not reached at this time, and no red ribbon appears.