Effects of Al/NiCr Coatings on the Current-Carrying Tribological Performance of Hydrogenerator Collector Rings

In order to improve the surface condition of collector rings in hydrogenerators and to enhance the current-carrying characteristics and operational stability of the brush/ring tribo-pair，Al and NiCr coatings were deposited on the surface of 45 steel，a commonly used collectorring material，via supersonic plasma spraying technology.The arc-erosion resistance of the two coatings was evaluated using a self-developed current-carrying wear test rig，and the friction coefficient，contact resistance，and temperature-rise behavior of the Al and NiCr coatings were analyzed at different current densities (0－12 A/cm2).Results showed that both coatings exhibited good resistance to arc erosion，with the NiCr coating exhibiting superior arc-erosion resistance.After 10 s of arc erosion，the Fe content on the NiCr-coated surface was only 2.72%，whereas that on the Al-coated surface was 3.65%.Owing to its low hardness and the continuous Al2O3 oxide film formed on its surface，the Al coating exhibited a lower friction coefficient: the friction coefficient was 0.494 under the no-current condition and increased to 0.541 at a current density of 12 A/cm2.However，its contact resistance remained relatively high.In contrast，an oxide film with semiconducting properties formed on the surface of the NiCr coating，resulting in a lower contact resistance；at a current density of 12 A/cm2，the contact resistance of the NiCr coating was 0.792 Ω.At low current densities，the Al coating exhibited the smallest temperature rise due to its high thermal conductivity.At medium to high current densities，the NiCr coating exhibited more stable temperature rise，as it generated less heat.These findings provided guidance for selecting coatings for hydrogenerator collector rings，indicating that coating selection should comprehensively consider current intensity and service conditions to optimize the long-term reliability of current-carrying tribo-pairs.