Requirements for Condition Based Operation and Maintenance in Offshore Wind Farms
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Going offshore, wind energy technology has to improve design as well as maintenance strategies. Reliability of current technology will not provide satisfactory reliability and availability. Condition based O&M aims at reducing the overall effort for maintenance and at improved reliability. But to achieve these goals, it requires: -Well-known technology and knowledge about typical faults and critical weak points, -Distinct and early fault detection by online Condition Monitoring Systems, and -Reliable prediction of remaining life span for all critical subassemblies. Therefore, -Co-operation between manufacturers, operators and scientists, -Comprehensive fault statistics on wind turbines components and -Detailed knowledge about the physics of damage progression and -Observation of data from condition monitoring systems detecting typical faults are needed. Presently, these items are not yet satisfactory fulfilled. Thus, the wind community has to put an effort on an improvement. The paper will address briefly the most important items to achieve this improvement. The paper will also describe a new German research project, which will yield offshore WT operational experiences, the so called OWMEP, a follow-up programme to the former (onshore) WMEP, accompanying the German "250 MW Wind" programme.
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... The simplest strategy (reactive) is the break down maintenance strategy, which is shown by the red dashed line. This method differs strongly from the other strategies (preventive) described, because the system will be operated until a major failure of a component will result in a shut down [1]. In contrary to the reactive maintenance also preventive strategies are applicable. ...
Modern wind turbines achieve a quite high availability of more than 95%. Nevertheless, quite a number of faults cause unscheduled down times up to ten per year, resulting in high maintenance efforts, production losses and costs. However, the common way of documenting faults and maintenance activities manually in paper form is currently not suitable for standardised and automated statistical evaluations. Therefore operational experience can seldom be used to improve design and maintenance procedures. For that reason a consortium of owners, operators, services-providers and researchers exploit experience with WT operation more intensively. The focus is on proposals for standardising data acquisition, data transmission and on a library for characteristic reliability values. Objective is to allow statistical analyses of reliability characteristics of wind turbines and subassemblies.
... The simplest strategy (reactive) is the break down maintenance strategy, which is shown by the red dashed line. This method differs strongly from the other strategies (preventive) described, because the system will be operated until a major failure of a component will result in a shut down [8]. ...
Rotor blades are highly loaded components of wind energy converters. Even in normal turbine operation, stress to the blades and to the supporting structure of a wind energy converter is quite high. Additional loads may be caused by fault conditions. Latest experiences with larger turbines point to the fact, that at least once in the designed lifetime a complete revision of the blades is recommended. This can also include blade replacements. Up to now condition monitoring of rotor blades is mainly done by visual inspections on site. Therefore, only "snapshots" of the actual rotor condition are provided. Furthermore, these inspections will become very problematic and cost intensive for offshore wind energy converters. So online condition monitoring of the rotor is strongly recommended, especially for wind energy converters in offshore wind farms. This will improve the operational safety and availability of offshore wind energy converters and contribute to avoid rotor fault conditions, which causes additional loads to the wind energy converter's tower and supporting structure. During the last years ISET has been developing and evaluating measurement technologies and algorithms for online condition monitoring and fault prediction of rotors. Main scope of the work has been the overall condition of the blades (surface roughness and icing) and rotor asymmetries (mass imbalance, aerodynamical asymmetry, yaw misalignment). This paper describes some of the results of ISET's research work related to online rotor condition monitoring. A description of the fault effects on the rotor, the sensor and data acquisition equipment and a description of the developed signal processing and fault prediction algorithms will be given. The paper also presents results from field tests.
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