When the electric locomotive pantograph is dropping, the interruption of pantograph catenary contact causes electromagnetic oscillation and arcing. The frequent arc burning that occurs due to charge accumulation results in the amplitude of overvoltage increasing gradually, posing a threat to locomotive high-voltage equipment. However, the physical mechanisms and characteristics of overvoltage are still unclear. This paper proposes a simulation model of operating overvoltage due to a dropping pantograph based on the pantograph–catenary arc and variable capacitance. Distributed RLC electromagnetic oscillation is considered, which allows the real-time calculation of arc resistance and capacitance. Under the same working conditions, the error between the simulation and test results is less than 4.0%, which proves the credibility of the model. The variation law of overvoltage under different dropping speeds or catenary phases was investigated, which shows the max amplitude is 298.20 kV and steepness is 2096.80 kV/μs at 0.30 m/s speed. The waveform shows the characteristics of high amplitude and high steepness, similar to very fast transient overvoltage (VFTO). There is a sinusoidal relationship between the catenary phase and overvoltage amplitude. The closer the catenary phase to 90°, the higher the overvoltage amplitude. The research has important guiding significance for the overvoltage formation mechanism of a traction power supply system and the insulation coordination design of high-voltage equipment.

Adding an insulating sheath to the exposed metal part of the outer insulation of a roof cable terminal can extend the creepage distance of the leakage current and significantly reduce the probability of pollution flashover on the outer insulation of the equipment. However, during the actual operation of the locomotive, the inner surface of the insulating sheath is discharged, resulting in cable insulation breakdown, the mechanism of which is unclear. This paper establishes a cable terminal–sheath electric field simulation model and studies the interface air gap, the interface with wet pollution, and the distribution of damp pollution on the outer surface and other factors on the electric field distribution of the cable terminal–sheath structure and the interface discharge, revealing the mechanism of discharge on the inner surface of the cable terminal’s insulation sheath. A voltage of 25 kV rms is applied, and the simulation results show that when the outer surface of the cable terminal is clean and there are air gaps and wet dirt on the inner surface, the maximum distortion electric field at the inner surface is 0.8 × 10⁵~3.4 × 10⁵ V/m, and the value of the electric field at this time is not enough to cause a partial discharge; when there is a uniform layer of wet dirt on the outer surface of the cable terminal, the electric field on the inner surface averages 1.5 × 10⁵ V/m, which is about 275% higher than the average electric field when the outer surface is clean; when there is wetting or an air gap on the inner surface at the same time, the maximum aberration electric field on the inner surface is 1.8 × 10⁵~1.9 × 10⁶ V/m. The wetting on the outer surface of the cable terminal strengthens the non-uniformity degree of the distribution of the electric field, and when there is wetting and an air gap on the inner surface, the over-voltage on the cable terminal inevitably leads to a discharge phenomenon in the air gap. This provides a theoretical basis for optimizing the insulation sheath structure to solve the discharge problem.

The zinc oxide (ZnO) arrester is positioned on the locomotive roof, preventing other onboard electrical equipment from being harmed by external and internal overvoltages. A number of locomotive arrester burnout and explosion accidents occur during traction supply network harmonic resonance, causing train stoppages and power outages in the network. This study first carries out high-frequency tests to investigate the wide frequency band electrical characteristics of the locomotive arrester and prove that the arrester is prone to fault during resonance. Consequently, a prognostics and health management (PHM) methodology for locomotive arresters is proposed, providing online monitoring, fault warning, and health assessment, which is beneficial to the operation and maintenance of arresters in the future.

The zinc oxide (ZnO) arrester is positioned on locomotive roof preventing other onboard electrical equipment from the harm caused by external and internal overvoltages. A number of locomotive arrester burnout and explosion accidents occur during traction supply network harmonic resonance causing train stoppages and power outages in the network. This study firstly carries out high-frequency tests to investigate the wide frequency band electrical characteristics of the locomotive arrester, explaining that the arrester is prone to fault during resonance. Consequently, a prognostics and health management (PHM) for locomotive arrester is proposed providing on online monitoring, fault warning and health assessment solutions, which is beneficial to the operation and maintenance of arresters in the future. The testing method and PHM scheme presented in this paper can be not only applied to the arrester, also readily expanded to other high-voltage electrical equipment on the electric locomotive.