Fleet Monitoring and Site Specific Environmental and Operational Conditions in Wind Energy

Abstract

In wind energy, the objective of fleet monitoring is to achieve the best possible energy yield and to early detect upcoming defects or not optimally adjusted turbines. If a vibration-based SHM system like SHM.Blade® is installed on all turbines of a wind park, an upgrade to fleet monitoring is possible. In the case of fleet monitoring, the vibration level of all turbines in a wind farm is related to their current yield. In general, the assumption is that all turbines in a park have more or less the same energy input and therefore can generate the same amount of electrical energy. Significant deviations from this, caused e.g. by false control, aerodynamically problems, mass imbalances, or damages, reduce the capacity of electricity production. A wind turbine is designed to convert the kinetic energy of wind into torque of the drive train. Therefore wind speed is the most decisive parameter for energy production of a turbine. The amount of energy that can be obtained from wind increases under ideal conditions with the third power of the wind speed. However the wind speed on site depends on different influences like e.g. turbulences in the lee of another turbine, wind park related difference in the height above sea level of individual turbine sites and the roughness of the ground. Therefore you cannot compare the energy yield of two turbines even if their locations are only some few 100 meters apart. The site specific difference in wind speed respectively the site specific efficiency is too big. Figure 3 shows the positions of three wind turbines in an existing wind park. The distance between the turbines is about 500 meters. However the efficiency factor related to the situation in the wind park differs considerably between 90,8% and 95,7% (see TABLE ). That means even very few meters difference with the height of the site and differences of roughness etc. can add together to an amount which is bigger than e.g. the influence of a misadjustment of the pitch angle. For that reason site specific Environmental and Operational Conditions (EOCs) have to be eliminated first before doing successful fleet monitoring. The paper will exemplify by means of real examples the importance of fleet monitoring and the necessity of EOC consideration within fleet monitoring of wind turbines