[4E3] Review of the shaft current in large-scale wind turbine: causes, suppression and monitoring techniques
M Yiming¹, Z Weijian¹, Y Yusheng², L Wei³, S Ziqi⁴, Y Shixi⁵ and G Xiwen⁵
¹Zhejiang Haifeng New Energy Technology Development Company Ltd, China
²Zhejiang Provincial Energy Group Company Ltd, China
³Zheneng Jiaxing Offshore Wind Power Company Ltd, China
⁴Zhejiang Energy Technology Research Institute Company Ltd, China
⁵Zhejiang University, China
Large-scale wind turbines in China have experienced rapid development in recent years, driven by strong market demand and supportive policies. Various original equipment manufacturers display homogenisation in drivetrain configurations and generator types, with permanent magnet medium-speed semi-direct drive units currently being the mainstream choice, featuring fully integrated designs for drivetrain connections and support structures. However, the generator bearings and high-speed stage bearings of the gearbox face an increasing risk of electrical erosion. This paper explores the formation mechanisms of different types of shaft current in mainstream wind turbine systems and evaluates common measures for suppressing these currents. The results indicate that modified pulse width modulation (PWM) methods, shaft grounding and bearing insulation do not fully eliminate common-mode and differential-mode voltages. Single-end insulation or grounding methods may even increase shaft voltage in adjacent bearings. Therefore, online monitoring of shaft voltage is crucial to avert irreversible damage due to electrical discharge from ineffective preventive measures. Based on a comparison of shaft current monitoring technologies, this paper recommends implementing comprehensive monitoring by integrating grounding current monitoring, Rogowski coil shaft voltage monitoring and vibration monitoring.
