Objective Wind turbine generator systems (WTGS) are prone to various failures due to harsh operating environments. As a central component of the transmission system, the main bearing has early failures that are difficult to detect and evaluate; additionally, offshore operations are constrained by limited weather windows. How to accurately assess the operating conditions of main bearings in offshore units has become a major challenge for the industry.

Method This study focused on the operating condition of the main bearing in a 7 MW offshore direct-drive generator. The transmission process of wind wheel loads in the transmission chain was derived using theoretical formulas, and the radial and axial loads on the main bearing were obtained. Via finite element calculation and analysis of the main bearing, the load distribution in the bearing raceway was obtained; this was cross-verified with the theoretical derivation, and the positions of vibration monitoring points were preliminarily determined.

Result Finally, based on the positions of bearing measuring points, vibration monitoring was conducted at the WTGS site, and clear time-domain vibration curves were obtained. Vibration monitoring results—including the vibration effective value of the main bearing, impact signal response frequency, and acceleration envelope characteristics—were analyzed. Combined with the test results of grease composition inside the bearing, the damage degree of specific components in the main bearing was qualitatively determined.

Conclusion This study has identified the positions of measuring points for main bearings in multi-megawatt direct-drive offshore WTGS and accurately assessed the operating conditions of main bearings. It can thus provide technical support for design and maintenance personnel.