Analysis of pitch system data for condition monitoring

Measurements of pitch motor torque and current give indirect information about the condition of the pitch system and can therefore potentially be used for condition-based maintenance. This paper presents an analysis of these measurements for a wind turbine, and the measurements are compared with a theoretical model based on aeroelastic simulations. The blade moment is found to have only minor influence on the friction in the blade bearing. The main factors affecting the static friction are the temperature and time after the latest pitch movement. Pitch motor current and torque are proportional at a constant pitch velocity, but the 10 min maximum values are only approximately proportional, because the maximum values occur during acceleration and not simultaneously. These findings are important to consider, if using the pitch motor current or torque as an indicator for the pitch system health is considered.