Pitch System Input Contribution on Wind Turbine Main Shaft Bearing Currents

Journal article, 2026

Drivetrain reliability is a critical challenge for modern large-scale wind turbines, with electrically induced main shaft bearing currents acting as a major threat to bearing longevity. This paper investigates common-mode voltage (CMV) propagation in wind turbines by comprehensively evaluating and comparing two distinct industrial pitch power topologies: grid-connected and converter-linked configurations. Numerical finite-element simulations demonstrate that slip ring parasitic capacitance and tower cable inductive coupling serve as the dominant transmission pathways to the drivetrain. Our analysis reveals a crucial finding: the coupling magnitude and spectral complexity of the main bearing voltage are highly dynamic, governed by the primary transmission mechanism where intermodulation sidebands dominate the converter-linked circuit, whereas discrete grid-harmonic unbalances dictate the grid-connected baseline. Based on these mechanisms, equivalent circuit models are established to derive the bearing voltage ratio (BVR) under various operation states. The proposed theoretical and simulation frameworks are fully validated through multi-level experiments, encompassing both white-box laboratory tests and on-site wind turbine measurements. The quantitative insights obtained from this study provide a solid analytical framework and concrete guidance for optimizing subsystem insulation and implementing targeted mitigation strategies in future wind turbine designs.