**5. Conclusions**

**Figure 18.** Flowchart of the condition monitoring and assessment process.

number of technical requirements, like high reliability, safety and up to 25 years of operating life. Due to its complex structure and variable conditions, gearboxes have been and still are a source of failure and so have been paid more attention in the industry. Nowadays, the capacity of the multistage planetary wind turbines that are installed is up to the megawatt power classes. Hence, it is important to point out that the reliability of wind turbine gearboxes has

The current reliability research methods of the wind turbine gearbox include finite element method (FEM), lumped mass method (LMM), statistical methods based on database, experiment method (EM), simulation with software, and so on. Statistical methods based on data-

The researchers in national renewable energy laboratory (NREL) have done much milestone work. Generator and gearbox models have been produced in Matrix Laboratory (MATLAB) and NREL's Fatigue, Aerodynamics, Structures and Turbulence (FAST) [12]. NREL proposed that it is essential to bring all the parties involved in the gearbox-design process together to achieve the common goal of improving the reliability and lifetime of gearboxes [13]. The effects of different constant rotor torque and moment conditions and intentional generator

The condition monitoring and fault diagnosis based on condition monitoring system (CMS) and supervisory control and data acquisition (SCADA) are also popular in wind turbine industry. The whole condition monitoring and assessment process within the system boundary include hard platform, condition monitoring and administrators of wind farms. Hard platform for wind farms includes the wind turbines, meteorological stations and monitoring data

misalignment on gearbox motion and high-speed shaft loads are examined [14].

great influences on wind turbines.

182 Stability Control and Reliable Performance of Wind Turbines

base are most commonly used.

In order to solve reliability problems in wind power industry, scholars all over the world proposed many methods. But these reliability analysis methods mainly focus on gear transmission systems of wind turbines and ignore the influences of other systems. The effects of the reliability analysis are limited if the system is simplified and seen as a series or parallel connection. Based on the abovementioned analysis and field research, some key conclusions are proposed:

(1) The reliability research based on the fatigue life.

The fatigue failure is the common failure modes of wind turbines. It needs to study the whole wind turbine fatigue life and reliability. With design parameters and the dynamic model, the failure correlation of key components is calculated. Following this, matrixes of loads and contact stresses can be calculated considering the operation environment of wind turbines. Finally, it is possible to produce the fatigue cumulative damage of key components.

**Author details**

China

**References**

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Council; 2014

Caichao Zhu\* and Yao Li

\*Address all correspondence to: cczhu@cqu.edu.cn

BTM Navigant Wind Report; 2015

The State Key Laboratory of Mechanical Transmissions, Chongqing University, Chongqing,

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(2) The gradual change mechanism and physical representation of component health status.

Combining loads and fault statistical data, the gradual change mechanism of health status needs to be studied with the function of key components and mechanism characteristics, and to seek the physical representation that is related to the component health status. This is helpful to develop the trend model and thresholds of the physical representation of fault status. Following the abovementioned method, it is possible to assess and pre-estimate the reliability of components and subassemblies.

(3) Reliability research based on the whole wind turbine's dynamics.

Considering the influences of the random wind speed and waves, the dynamic model is established including components from blades to the foundation, by which the dynamic reliability of the wind turbine structure and drivetrain is studied. Following this, it is possible to evaluate the dynamic reliability of the whole wind turbine. However, the current reliability research ignored the influences of waves on the foundation and the tower, which would bring big errors to the reliability research. Therefore, it is essential and urgent to develop a set of the reliability engineering model and test method of wind turbines considering the influences of waves and the sea wind.

(4) Remote real-time assessment system of the wind turbine reliability based on the fusion data.

It is clear that most wind turbines have been installed both SCADA and CMS, but they are independent and cannot achieve the mutual support of test results. Therefore, it is meaningful to mix two sets of the test data based on SCADA and CMS. Following this, the feature data can be extracted and transferred to the data center by the Internet. When the feature data reach the data center, they can be used to calculate and assess the dynamic reliability of wind turbines through engineering models and hardware and software equipment immediately, which will cut the operation and maintenance cost and improve the operating efficiency of wind turbines sharply.
