Review of failures and condition monitoring in wind turbine(2)

Fixed pitch where blade angles are fixed and variable pitch wind turbines.

Wind turbines equipped either with squirrel-cage induction generators or wound rotor induction generators (DFIG) with frequency converter on the rotor side (indirect drives) and multi pole synchronous generators with fully frequency converter and without gearbox (direct drives).

Directly connected to the power network and connected via frequency converter.

A wind turbine is composed of the rotor which extracts kinetic power of air to produce mechanical torque, the main bearing, the gearbox which converts high torque-low speed rotational power to high speed-low torque rotational power, the generator which converts the mechanical torque into

Nacelle

Fig. 2. Wind turbine components [33].

III. WIND TURBINE FAILURES

Wind turbines are subjected to different sorts of failures. Some of them are more frequent than others but in order to compare them it is necessary to consider the downtime they could force for the whole system. Therefore, wind turbine

failures statistics should be studied by considering both failure frequencies and downtimes. Unfortunately, the access to wind turbine failures statistics is not always permitted by the manufacturer and it is completely understandable. Thus, this paper refers to the latest available data [4] for wind turbines failures on 2004 (Fig. 3). Fig. 3. Distributions of number of failures compare to down time per component for Swedish wind power plants between 2000-2004 [4].

As shown, the distribution of failures and downtimes for each component of wind turbines are compared and it is clear that most of the failures are linked to the electrical system, the different sensors, the blade pitch and the control system respectively. In case of downtimes per component, the gearbox and the control system have the highest rate compared to the other components.

Some recent works report that the gearbox with average downtime of 256 hours per failure and 6,057 hours downtime per year has the highest downtime and it is well known that it is the most critical component of the wind turbine [3], [4]. A further analysis shows that the control system has almost the same situation as the gearbox in term of downtime per failure (184.6 hours) and average downtime per year (5,724 hours).

The number of failures per operational year is another

noticeable issue in wind turbine failures statistics. It has been shown that the number of failures in the first operational year is much lower than in the second one [3], [4]. Then, the rate of failures is approximately constant for eight years and it drop at 11th year. Then, in the 12th year there is an important peak and after it decreases to go upward till the 19th year.

As the gearbox is the most critical part in indirect drive wind turbines, it might be supposed that direct drive wind turbines have fewer failures than the others. In fact, a study on different types of wind turbines shows that direct drives wind turbines do not have less failures than indirect drives [5]. An investigation related to the generators and obvious. Therefore, accurate condition monitoring and fault diagnosis are almost mandatory. Condition monitoring systems select and survey measurable parameters from any wind turbine which will change as the health or the condition of machine operation changes [36]. When a change is detected, detailed analysis of the measurement will be provided and the diagnosis of the problem will be performed. Wind turbine condition monitoring systems allow collecting data from the main components of a wind turbine such as the generator, the gearbox, the main bearing, the shaft and the yaw system. The purpose is to minimize downtime and maintenance costs while increasing the energy availability and the life time service of wind turbine converters reliabilities in wind turbines has been done in [5] and it establishes that (Fig. 4):

Power converter failures in direct drive wind turbines are more important than in indirect drive but it is far smaller than of the gearbox.

The failure rate of the electric system is notable in direct drives and considering all electrics failure together, their failure rate is significantly more important than the gearbox failure rate in indirect drive. Generator failures rate in direct drives are twice of in indirect drives.

Fig. 4. Comparison of the failure rates in different wind turbine concepts

[5].

Therefore, total failure rate in direct drive wind turbines is not less than in indirect drives. A complete comparison of direct drive and indirect drive wind turbines have been done in [35] based on their cost and annual energy efficiency. The condition monitoring requirement in wind turbines have been analyzed in several works. In a recent analysis [6], the life cycle cost (LCC) analysis with wind turbine condition monitoring existence has been presented. This LCC analysis has been done for several strategies showing that condition monitoring systems are completely profitable. Moreover, it has been indicated that the gearbox is most critical component of the wind turbine and when a failure occur in a gearbox it would stop the power generation for 256 hours in average. So, in order to increase a gearbox lifecycle, early failure detection is important [7]. Some of the gearbox failures lead to long time repair if it is not predicted by condition monitoring.

IV. CONDITION MONITORING

By increasing the wind power generation quantity in power systems, the need of a reliable operation becomes components.

Wind turbines are complex electromechanical systems and their maintenance is usually costly and it depends on the maintenance method. Some maintenance methods as corrective maintenance could take more time than others. Generally, the maintenance is defined either as predic …… 此处隐藏：6247字，全部文档内容请下载后查看。喜欢就下载吧 ……