Operational Modal Analysis of Operating Wind Turbines: Application to Measured Data

Abstract

Previous works by the authors have shown that though Operational Modal Analysis (OMA) techniques are suitable for global dynamic analysis of a wind turbine under parked conditions, there are several issues in their application to operational wind turbines. These issues including time varying nature of the structure, presence of harmonic content in the loading (due to rotor rotation), considerable aerodynamic damping etc. prevent straightforward application of OMA to operational wind turbines. The authors have further proposed a strategy to combat these issues and modify OMA methodology to tune it for operational wind turbines. A successful implementation of this strategy was employed and demonstrated to work satisfactorily on simulated vibration response data for a 3MW wind turbine. Work presented in the current paper in an extension of the pervious work and describes the details of the measurement campaign aimed at identifying modal parameters of ALSTOM’s ECO 100 wind turbine. Since measuring on an operational wind turbine is a challenging job in itself, the paper also describes measurement planning and execution phases. The paper illustrates various key aspects related to practical measurements on an actual wind turbine and underlines the importance of proper planning and experiment design. The importance of a priori knowledge provided by finite element model based simulations is also underlined.