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As a collector ring material, carbon steel is widely used in domestic active hydraulic generators and high-speed current-carrying friction systems. However, during operation, the carbon brush/collector ring friction pair may lose contact due to the rotor's eccentric vibration, leading to electric sparks or ring fires at the contact interface. These occurrences result in mechanical wear and electrical corrosion, seriously endangering the normal operation of the unit. To clarify the underlying mechanism, this study investigated the evolution of electric spark strength at the interface of D172 carbon brushes and 45# steel, as well as the change in the surface ablation degree of 45# steel under various conditions of load, speed, and polarity. The results demonstrate that under the same load, the relative strength and discharge characteristics of electric sparks are influenced by polarity and rotation speed. Specifically, the arcing rate, maximum relative strength, average relative strength, and maximum duration of electric sparks exhibit positive correlations with rotation speed. As the rotating speed increases, the electric spark of carbon brushes connected to the positive pole gradually transitions from multiple points/columns to strips. On the other hand, the electric spark of carbon brushes connected to the negative pole gradually evolves into spherical/ellipsoidal shapes and shows splashing effects with the increasing rotating speed. Additionally, the degree of surface ablation increases with the velocity, and the ablation is greater in the case of carbon brushes connected to the negative pole compared to those connected to the positive pole.
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