Electrochemical Response Characteristics During the Oxidative Degradation of Gear Oil in Wind Turbine Generators

Oxidative degradation stands as the principal cause of gear oil failure and transmission system malfunctions in wind turbines. Electrochemical impedance spectroscopy (EIS) offers a novel technical avenue for the condition monitoring of gear oil. This research centers on the evolution mechanism of electrochemical properties during the oxidative degradation process, utilizing high-viscosity gear oil commonly employed in wind turbines as the research subject. Through a combination of accelerated oxidation tests, broadband EIS measurements, and equivalent circuit fitting, the study examines the variations in the electrochemical response of gear oil with respect to oxidation temperature and duration. The findings reveal that oxidative degradation does not modify the single-relaxation dielectric characteristics of the gear oil; however, various electrochemical parameters undergo systematic evolution. Following oxidation at temperatures ranging from 90 to 120 °C, the charge transfer resistance escalates by approximately 5.9-fold; the base resistance diminishes by 10% to 20%; both the admittance constant and dispersion index of the constant phase element (CPE) exhibit changes of less than 5%, indicating that the system retains its capacitive properties. During constant-temperature oxidation at 90 °C for durations spanning 50 to 175 h, the charge transfer resistance increases in an approximately linear fashion with oxidation time, while the base resistance continues to decline, and the CPE parameters remain largely stable. Various electrochemical parameters evolve monotonically with the extent of oxidation, with charge transfer resistance demonstrating the highest sensitivity to thermal oxidation and thus serving as a pivotal indicator for evaluating the degree of thermal oxidative degradation in gear oil. This study lays an experimental foundation for the application of EIS technology in the realm of online gear oil monitoring.