The concept of reliability-centered maintenance (RCM) is applied to the two wind-turbine models Vestas V44-600 kW and V90-2MW. The executing RCM workgroup includes an owner and operator of the analyzed wind turbines, a maintenance service provider, a provider of condition-monitoring services, and wind-turbine component supplier as well as researchers at academia. Combining the results of failure statistics and assessment of expert judgement, the analysis is focused on the most critical subsystems with respect to failure frequencies and consequences: the gearbox, the generator, the electrical system, and the hydraulic system. This study provides the most relevant functional failures, reveals their causes and underlying mechanisms, and identifies remedial measures to prevent either the failure itself or critical secondary damage. This study forms the basis for the development of quantitative models for maintenance strategy selection and optimization, but may also provide a feedback of field experience for further improvement of wind-turbine design.

In view of the frequent and costly failures of power converters in wind turbines, a large consortium of research institutes and companies has joined forces to investigate the underlying causes and key driving factors of the failures. This paper presents an exploratory statistical analysis of the comprehensive field data provided by the project partners. The evaluated dataset covers converter failures recorded from 2003-2017 during almost 7400 operating years of variable-speed wind turbines of different manufacturers and types, operating at onshore and offshore sites in 23 countries. The results include the distribution of failures within the converter system and the comparison of converter failure rates among turbines with different generator-converter concepts, from different manufacturers as well as from different turbine generations. By means of combined analyses of converter-failure data with operating and climate data, conditions promoting failure are identified. In line with the results of a previous, much smaller study of the authors, the present analysis provides further indications against the wide-spread assumption that thermal-cycling induced fatigue is the lifetime-limiting mechanism in the power converters of wind turbines. Instead, the results suggest that humidity and condensation play an important role in the emergence of converter failures in this application.

Maintenance of offshore wind power plants is known to be extensive and costly. This paper presents a model for optimizing the maintenance support organization of an offshore wind farm: the location of maintenance accommodation, the number of technicians, the choice of transfer vessels, and the use of a helicopter. The model includes an analysis of a transportation strategy using alternative transportation means, a queuing model of maintenance activities, and an economic model of the maintenance support organization. An example based on a generic 100 wind turbine 5-MW wind farm is used to demonstrate the application of the model. The results show the benefit of the production losses of the different options, which enables the identification of an optimal maintenance support organization based on the reliability, logistic costs, and electricity price. The most cost-efficient maintenance support organization in the case study consists of an offshore accommodation with technicians on service 24 hours a day, 7 days a week. The solution suggests transportation by use of a crew transfer vessel equipped with a motion compensated access system.

The frequent power-converter failure experienced in wind turbines has a strong economic impact through both the related turbine unavailability and the maintenance cost. Up to now, the prevailing mechanisms and causes underlying the converter failure in wind turbines are mostly unknown. Their identification is, however, a prerequisite for the development of effective solutions. This paper describes a multitrack empirical approach to failure analysis including systematic field-data evaluation, exploration of the real converter operating environment, and postoperational laboratory investigation of converter hardware. The analysis is carried out for two widely used multi-MW wind turbines with low-voltage, insulated-gate bipolar transistor-based converters (topology 1: doubly fed induction generator with partially rated converter, topology 2: induction generator with fully rated converter). The findings suggest that the principle failure mechanisms of power electronics found in other applications, namely solder degradation and bond-wire damage, play a minor role in the investigated types of wind turbines. Instead, the analysis reveals indications of insufficient protection of the converter hardware against the environment (salt, condensation, and insects) as well as indications of electrical overstress.

Power converters are among the most frequently failing components of wind turbines. Despite their massive economic impact, the actual causes and mechanisms underlying these failures have remained in the dark for many years. In view of this situation, a large consortium of three research institutes and 16 companies, including wind-turbine and component manufacturers, operators and maintenance-service providers has joined forces to identify the main causes and driving factors of the power-converter failures in wind turbines to create a basis for effective remedial measures. The present paper summarizes and discusses the results of this research initiative, which have been achieved through the evaluation of converter-specific failure and operating data of a large and diverse worldwide wind-turbine fleet, field measurements as well as post-mortem investigation of returned converter components. A key conclusion of the work is that the thermal-cycling induced fatigue of bond-chip contacts and die-attach solder, which is a known issue in other fields of power-electronics applications and which has been widely assumed to be the principle damage mechanisms also in wind turbines, is no relevant contributor to the observed converter failures in this application. Instead, the results indicate that environmental factors such as humidity and contamination but also design and quality issues as well as human errors play an important part in the incidence of these failures.

The authors develop a stochastic model for assessing the life‐cycle cost and availability of wind turbines resulting from different maintenance scenarios, with the objective to identify the most cost‐effective maintenance strategy. Using field‐data‐based reliability models, the wind turbine – in terms of reliability – is modelled as a serial connection of the most critical components. Both direct cost for spare parts, labour and access to the turbine, as well as indirect cost from production losses are explicitly taken into account. The model is applied to the case of a Vestas V44–600 kW wind turbine. Results of a reliability‐centred maintenance analysis of this wind turbine are used to select the most critical wind turbine components and to identify possible maintenance scenarios. This study reveals that corrective maintenance is the most cost‐effective maintenance strategy for the gearbox and the generator of the V44 turbine, while the cost benefit of condition‐based maintenance using online condition‐monitoring systems increases with higher electricity price, turbine capacity and remoteness of sites.