Contribution study of different common mode voltage sources on wind turbine main shaft bearing currents

Journal article, 2026

Main shaft bearing failures in wind turbines have drawn increasing attention due to their high maintenance costs and operational risks. While previous studies have primarily focused on mechanical causes or bearing currents induced by generator-side common-mode voltage (CMV), limited attention has been given to other sources and system-level interactions. This paper addresses these gaps by presenting a unified modeling framework that captures CMV contributions from both the generator and the pitch system—each driven by pulse-width modulation (PWM) inverters. An equivalent capacitive circuit model is developed based on parasitic capacitances among key subsystems, including the generator, pitch motor, hub, shaft, and grounding paths. The bearing voltage ratio (BVR) is derived using the superposition principle to quantify the influence of each CMV source. The model accommodates different turbine configurations, such as geared and gearless systems, enabling analysis of architecture-dependent behaviors. Critical interface parameters are also identified and evaluated through sensitivity analysis. Experimental validation is conducted using a custom test platform and simulation model, confirming the accuracy of the proposed approach. The findings offer new insights into the role of different system CMVs in shaft voltage buildup and provide guidance for more effective design and mitigation strategies in wind turbine systems.