Reliability of technical systems

Fatigue Strength and Fatigue Test of Drive Train Components

Fatigue strength and life cycle are two key elements in the design of a wind turbine, guaranteeing a safe operation and high availability of the product. The increasing power output of wind turbines and the often accompanying up-scaling processes show new and unexpected effects. The utilization of large testing facilities allows to verify prevailing design processes of large components, increase the safety of the dimensioning  and to make weight savings possible. Theoretical models for component dimensioning and processes for accelerated life cycle tests can be improved or validated and findings can be transferred to other components; the research project "BeBen XXL" is one example, scrutinizing the main bearings of wind turbines.

Further activities

Condition monitoring systems (CMS) are applied to detect damages of drive train components in an early stage. They enable the operator to take precautionary action and adjust the maintenance and operation schedule. The repair costs can be lowered by preventing heavy damages and consequential damages to the turbine components. Repair works can be planned ahead which commonly reduces the turbine’s downtime.

In certain cases, e.g. the detection of imbalances and misalignments in the drive train, the CMS can completely avoid the emergence of damages. CMS plays an essential role for the technical availability of the wind turbine. Furthermore CMS is the basis of a stateful maintenance strategy, that avoids unpredicted failures and on the other hand makes the most of the life cycle of the components. Therefore CMS is often the key to the most economical way of maintaining a wind turbine.

Our key areas are

- Conceptual design, design, implementation and test of novel condition monitoring systems for multi-megawatt onshore and offshore wind turbines. We combine model based turbine observers and purpose-built sensor technology for model comparison.

- CMS based prognosis of the remaining lifetime of drive train components, through the analysis of failure and CMS data of turbines of the same type

About 20 to 30 per cent of the life-cycle costs of a wind turbine are caused by operation and maintenance. The major share is related to service and maintenance and especially the maintenance after failures and the overhaul of damaged components. In addition to an adequate service and maintenance strategy it is essential to increase the reliability of affected components to reduce these costs. A fundamental requirement to increase the reliability, e.g. through design adjustment or retrofit solutions, is the identification of the failure causes and mechanisms.

For this reason we conduct root cause analyses based on operation and failure data analysis (SCADA and maintenance data, environmental influences amongst others), complemented by field measurements and laboratory examination of the damages. Our current main research field are power electronical frequency converters.

Power Electronics for Regenerative Energy Supplies Innovation ClusterReliable Power Electronics

Lower Saxony lead project, coordinated by Fraunhofer IWES

Operation and maintenance account for around a third of the life cycle costs of wind plants. System reliability will play a central role in the further sinking of LCOE for wind turbines. At the same time, the focus should be on the components which represent the principal cost drivers due to higher failure rates / longer downtimes. This is particularly applicable to the power electronic frequency converters used in practically all modern wind turbines nowadays.

As the connector between the generator and system transformer, they are used for the power-frequency connection of variable speed wind turbines to the power supply grid. They ensure compliance with the grid connection conditions and permit optimal utilisation of the available wind. The combination of dynamic loads typical of wind and extreme environmental conditions places particularly high requirements on the power electronics.

This project is aimed at comprehending the, as yet, still not understood causes and mechanisms of the frequently occurring damage to power electronic wind turbine components and developing solutions based on this knowledge in order to increase reliability. In addition to extensive evaluation of field data and damage analyses in laboratories, simulation models will be optimised in order to be able to reproduce better the loads acting on power electronics whilst taking the overall plant dynamics during operation into consideration. The development of systems for early detection of faults in electronic plant components and the design of innovative, fault-tolerant generator/converter concepts for the next generation of wind turbines are additional focal points.

The spectrum of private enterprise partners ranges from plant management and maintenance companies to frequency converter and plant manufacturers through to insurance companies and enterprises specialising in measuring technology and condition monitoring. One particular feature of this project is the comprehensive, systematic integration of experiences gained in the field during the design, manufacturing and maintenance processes.

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