Wind Turbine Doubly-Fed Asynchronous Machine Diagnosis Defects State of the Art

Transcription

1 2017 2nd International Conference on New Energy and Renewable Resources (ICNERR 2017) ISBN: Wind Turbine Doubly-Fed Asynchronous Machine Diagnosis Defects State of the Art Fatima El Hammouchi, Lamia El Menzhi and Abdallah Saad ABSTRACT In this research paper, we will present the first works related to a state of the art and assess different defects found in two Moroccan wind turbine parks. In this respect, it is of paramount importance to shed light on these wind turbine parks and conduct a scientific research to analyze and come up with certain findings related to the issue under study. We are going to focus on the main defects that occur in wind turbines and thus we will sort out the most frequent ones in an attempt to provide an overall analysis of the system and its defects. INTRODUCTION Many countries have recently adopted a number of methods to face the depletion of fossil fuel and its skyrocketing costs and meet the increasing demand for energy. Thanks to the strategic and geographical location of Morocco, the country benefits from an enormous wind potential characterized by an annual average wind speed exceeding 10 meter per second in so many sites [1]. And being aware of this wind potential, Morocco has already installed a number of wind turbines in different parts Fatima El Hammouchi, National Higher School of Electricity and Mechanic, Hassan 2University, Casablanca 8118, Morocco. Lamia El Menzhi, National School of Applied Sciences, Abdelmalek Essaadi University, Tangier 9000, Morocco Abdallah Saad, National Higher School of Electricity and Mechanic, Hassan University, Casablanca 8118, Morocco. 300

2 of the country. According to Global Wind Energy Council statistics, Morocco is the third country in Africa and Middle East by 787 MW of global installed wind power capacity regional distribution cumulative in the end of 2016 [2]. Unfortunately, despite the fact that the wind potential is completely free, inexhaustible and renewable, its cost remains unaffordably high due to maintenance of such a big structure. The most efficient way for reducing the wind energy costs is to minimize the operational and maintenance costs which could be realized by continuous monitoring of the system condition [3]. Actually, wind turbine faults occur periodically once it starts working especially in blades, gearbox and generator [4]. Indeed, choosing the technique to diagnose the wind conversion system faults successfully allows early detection of the degeneration of the wind turbine health. For this purpose we present, in this state of the art, a study of the defects of two Moroccan wind turbine parks. PRESENTATION OF TWO MOROCCAN WIND TURBINE PARKS These Moroccan parks include the most common design of wind turbine in industry which is the horizontal-axis HAWT. The wind turbines, in our study, are implanted in two parks in close regions of Morocco in order to be exposed approximately to the same wind (direction and speed). Parks Characters The first park shelters 12 wind turbines, the rotor diameter of every wind turbines makes 52 meters. And the rated electrical power of each one is 850 kilowatt. The electrical power curve of wind turbines in park 1 is shown in figure 1 bellow. The second park is constituted of six wind turbines, the rotor diameter of each wind turbine is 80 meters. The electrical power curve of the 2 Megawatt wind turbine is illustrated in the following figure 2 below. Figure 1. Wind turbine power in park 1 as a function of wind speed. 301

3 Figure 2. Wind turbine power in park 2 as a function of wind speed. Figure 3. Main components of wind turbine. Main Components of Wind Turbine These Moroccan horizontal axis wind turbines are basically composed of: tower that supports the rotating blades and allows it to access strong wind, three blades that capture the kinetic energy of the wind, hub that is connected to the low speed shaft of the gearbox, actuators to control the pitch angle of the blade, yaw mechanism to rotate the nacelle in order to increase the exposure of the blade to wind, gearbox to increase the rotation speed, asynchronous generator to convert the mechanical energy into electrical energy, transformer to step up the voltage and many controllers that regulate the generated power and protect the turbine from grid faults and storms. All of these components are shown in figure 3. The main advantages of HAWT are the height of tower that allows the blades to receive maximum of power from wind at any position. Also, the speed of the blade is fairly constant during a single rotation, and rapid fluctuations in electrical variables such as voltage and reactive power are insignificant [5]. However, the HAWT requires high cost in installation and cumbersome maintenance [6]. Main Elements of Wind Energy Conversion System Nowadays, a Doubly-Fed Induction Generator (DFIG) is commonly used in wind turbine industry [7] for many reasons. In fact, the DFIG is an asynchronous 302

4 machine fed from the stator and rotor that allows variable speed and excellent performance; also it offers control features of active and reactive power. The wind causes the turbine to spin, the mechanical power enters from the main shaft to the rotor and it is converted into electrical power. The rotor is connected to the grid through the voltage source converters: rotor side converter (RSC) and grid side converter (GSC). A capacitor is placed between two converters to reduce the voltage ripples. The RSC controls active and reactive power, developed torque and speed of rotation. So, the GSC controls DC bus voltage and factor grid. The transformer is installed to set up the output voltage of the wind turbines to the network voltage levels. STUDY OF TWO MOROCCAN WIND TURBINE PARKS This part will be devoted to a study of defects in the abovementioned parks. The period of study is one year from October 2014 until September All the graphs and statistics below are realized in this period. Figure 4. Defect number of wind turbines in Moroccan park 1and park. Figure 5. The highest wind speed (m/s) from October 2014 to September Defect s Number of Wind Turbines We shall start our analysis by presenting two graphs showing a yearly defect number in these Moroccan parks. As indicated in figure 4 above the number of 303

5 defects in these parks is the highest in October and February while it partially decreases in the rest of the year. So, in order to evaluate the major causes of the defects in these parks it is necessary to get a clear idea about wind speed in this period of our study. Indeed, as it is shown in figure 5 above, the highest wind speed in February reaches a maximum value of 30.4 m/s. We deduce that the park with 80 meter in rotor diameter of wind turbines undergoes more defects than the park that harbors wind turbines with 52 meter in rotor diameter. Furthermore, in these violent winds of February the turbines are stopped to avoid overload, damage and destruction of the system. Also, the variability of speed and direction of wind is one of its biggest disadvantages as a source of energy. We must shutdown turbines when wind speed exceeds 25m/s; also when there is much power in the national grid and less demand from consumers. This operation of turning off and starting up the wind turbines can cause fatigue and high temperature of diverse components of the system and leads to mechanical and electrical defects. So, the investigation of defects types and occurrences can provide an approach to define a strategy reducing the operations and maintenance costs of Wind Energy Conversion System in order to extract maximum power. Types of Wind Turbine Defects There is a multitude of defects attacking these parks: defects caused by internal problems as well as mechanic defects like fatigue in wind turbines blades and vibration, or external ones due to grid faults and violent winds. In our study, we concentrate on different types of defects in two wind turbine parks. So, we mainly focused on four essential types of defects: electrical, mechanical, grid and strong wind related defects. The graphs below (figure 6) introduce the defect types for each park. This data collected from Moroccan parks allows us to conclude that the electrical defects represent approximately 50% of the defects in these wind turbine parks during one year. The highlight of the two parks is that a Doubly-Fed Asynchronous Generator was burned for each park in the sixth month of Besides, the two parks undergo several electrical defects. We mention: over-current in stator phases of the Doubly- Fed Asynchronous Generator DFIG, overvoltage in crowbar, over-current phase in Grid Side Converter GSC, thermal tripping in yaw drive motor because of Cable isolation fault, magneto-thermic release rotor protection, gearbox pump fault. Figure 7 illustrates one of electrical defects. The second type of defects in park 1 is a mechanical one; it makes 27% of defects in this park and it occurs mainly in gearbox (broken bearings, high misalignment, high oil temperature, etc.), electrical generator bearings, ring yaw motor, and also blades bearings. In the park 2, the grid fault has the highest percentage after the electrical fault by 22%. Wind turbines, connected to the grid are exposed to various grid faults such as lack of grid voltage and overheated generator 304

6 due to the short circuit in the grid. The electrical network is frequently described by variation in the voltage magnitude and by time duration. Actually, in order to make sure that the electrical defect is the major defect attacking these parks, it seems imperative to provide an overview on the frequency of defect types. Figure 6. Defect types of park 1 and park 2 from 2014 to Figure 7. A burned Insulated Gate Bipolar Transistor. Figure 8. Defect types of park 1 and park 2 from 2014 to

7 Wind Turbine Defect Occurrence The yearly data from 2014 to 2015 as indicated in figure 8 above prove that the electrical defects occur more than 358 times in these two parks. We conclude that the major defects attacking these Moroccan parks are the electrical defects. CONCLUSION AND FUTURE WORK In this paper we present a step toward better understanding of defects types attacking wind turbines in two Moroccan parks. The inspection of the annual data of defects proves that, if we can expect electrical defects we will minimize until 50% of defects in Moroccan wind turbines farm. There is no doubt that some publications dealt with this topic, however, with no data or statistical analysis included as is done in this study. The future work could focus on the diagnosis of the defects of double-fed asynchronous machine, their modeling based on a mathematical model created in MATLAB SIMULINK, and the efficiency of the proposed method. For this purpose, a method for preventing defects will be presented in case of a non-defected and defected generator. REFERENCES 1. M. Mustapha ENZILI. (2011) "The 6th Conference Morocco-Germany about the Wind Energy." Casablanca, Morocco. 2. The Global Wind Energy Council GWEC. (2017) "Global Wind Statistics 2016". 3. Y. Amirata, M.E.H. Benbouzida, E. Al-Ahmara, B. Bensakerb, S. Turria. (2009) "A brief status on condition monitoring and fault diagnosis in wind energy conversion systems", Renewable and Sustainable Energy Reviews Volume 13, Issue 9: A.Joshuva and V. Sugumaran. (2016) "Fault diagnostic methods for wind turbine: a review", in ARPN Journal of Engineering and Applied Sciences, VOL. 11, NO Mohamed A. El-Sharkawi. (2016) "Wind Energy An introduction", University of Washington, Seattle, USA: D. McMillan, G.W. Ault.(2008) "Condition monitoring benefit for onshore wind turbines: sensitivity to operational parameters", in IET Renewable Power Generation Volume 2, Issue 1: Kling WL, Slootweg JG. (2002) "Wind turbines as power plants", in Proceeding of the IEEE/Cigré workshop on wind power and the impacts on power systems, Oslo, Norway. 306