Analysis of high frequency harmonics injected by …

1 Analysis of high frequency harmonics injected by wind turbines in a local grid Master s Thesis in the Master Degree Programme, Electric power Engineering Jacob Eriksson Department of Energy and Environment Division of Electrical Engineering CHALMERS UNIVERSITY OF TECHNOLOGY G teborg, Sweden, 2012 Analysis of high frequency harmonics injected by wind turbines in a local grid Jacob Eriksson Department of Energy and Environment Chalmers University of Technology ABSTRACT This master thesis is conducted in cooperation with G tene Elf rening, a local distribution company in G tene kommun. In this report, noise propagation focusing on high frequency harmonics is studied. The purpose of this study is to study if the used method of investigating the high frequency noise in G tene elf renings grid injected by wind turbines is adequate to get a satisfying picture of the noise situation.

2 Furthermore, to study if the method provides a satisfying picture of the noise propagation and how the propagation itself affects the noise level. Consequently to evaluate if any means for harmonic mitigation are needed. Measurements of voltages and currents are performed at three different locations, at two different wind turbines and at a point of common coupling. From these measurements a frequency spectra and curves of voltages and currents are produced. This is then used to calculate the total harmonic distortion (THD). Comparisons between different power levels and operation settings are then preformed. According to the results of this study the level of high frequency noise injected to the grid by the wind turbines of interest are low.

3 At the point of common coupling the noise is decreased to a neglectable level. The conclusion of this study is that wind turbine installations containing power electronics in this specific grid does not cause power quality problems under the current conditions. Moreover it is found that the harmonics injected is so low that it was not possible to detect a difference when two various grid configurations were made during the measurements. Keywords: High frequency noise, wind power , measurement, converter, total harmonic distortion ACKNOWLEDGEMENT I would like to dedicate my greatest gratitude to my supervisor Tarik Abdulahovic at CHALMERS UNIVERSITY OF TECHNOLOGY. Further I would like to thank Johan Lundquist and Leif Blomgren at G tene Elf rening for giving me opportunity and help to perform measurements in their grid.

4 Jacob Eriksson 28th February 2012 ABBREVIATIONS W - Watt AC - Alternating current PWM-Pulse width modulation Vref - reference signal Vtri - triangular wave signal VSC - voltage source converter Hz -Hertz PLC - power line communication THD - Total harmonic distortion Is1 Fundamental current Is RMS value of the line current A - Ampere V - Volt Root mean square Z Impedance Zg - Source impedance Zc - Impedance or the wind park 1 Contents 1 Introduction .. 3 Background .. 3 Purpose of the study .. 4 2 Technical background .. 5 Components of a wind power installation .. 5 Inverter systems .. 5 harmonics .. 8 High frequency noise .. 8 Instability and damage .. 8 power line communication .. 9 TV and radio disturbances .. 9 Total harmonic distortion .. 9 Description of the wind power connection- and the grid in G tene.

5 9 wind 9 Grid .. 10 3 Method .. 12 Measurement point evaluation .. 12 Measurement equipment .. 12 Software .. 14 Measurements and results .. 14 Measurement at Enercon wind turbine E82 .. 14 Low production .. 16 Medium production .. 19 High production .. 22 Results from the Enercon E82 measurements .. 24 Measurement at Enercon wind turbine E53 .. 25 Low production .. 26 Medium production .. 30 2 High production .. 32 Result from the Enercon E53 measurements .. 35 Measurement at Point of common coupling .. 36 Normal operation, 20kV .. 36 Results: Induced noise level compared to noise level at point of common coupling .. 39 Decreased impedance, 20kV .. 41 Results: Decreased impedance, 20kV .. 43 Disconnected K llby cable, 20 kV .. 45 Disconnected K llby cable and phase compensation capacitor, 20kV.

6 46 Results from disconnected phase compensation capacitor measurement .. 47 4 Conclusions .. 49 5 Future Outlook .. 50 6 References .. 51 3 1 Introduction Background The world s electric power production is mainly based on nuclear, hydro and fossil fuels. In the last decade, the global warming phenomenon has become more and more discussed. The use of fossil fuels at the current rate is found to be unsustainable. The electric power production methods of today have to be reformed and the proportion of the fossil fuel based power production has to be decreased drastically. The best alternative considered today is the production of electricity by renewable power sources such as wind , waves and solar energy. Due to a very high potential and very competitive price, wind power is becoming more and more popular.

7 In the last decade the share of wind power turbines have increased significantly. Furthermore, the development of the wind turbines led to a significant increase in the power rating of the turbines. The turbines that are installed in Sweden today usually have a maximum power of MW. But there are turbines with a maximum power of 6 MW that are available on the market. It is clear that the development towards renewable energy sources has a positive effect on the environment, but there are the some issues related to this technology. Large electric power plants such as nuclear plants or hydro power plants are usually connected to the transmission grid while the wind turbines are often connected directly to the distribution grid. The problem is that the distribution grid is not intended for direct connection of power plants.

8 This obviously causes some problems for distribution companies. Their grids may no longer be efficient for handling the power levels and keeping a good power quality in their grid. This problem varies from one location to another and a few case studies are performed in this work. The focus of this work is the power quality of the power produced in the various wind power plants measured at different points. What distinguishes wind power from traditional hydro and thermal plants is the intermittent nature of this power source where the produced power is directly dependent on the speed of the wind . In nuclear plants and hydro power plants the power source is fairly easy to control and maximum production can be achieved according to grid requirements.

9 This is not true for wind power where the production is dependent on the speed of the wind . This means that the power produced is directly proportional to the wind speed. In order to improve the efficiency of the wind turbines and make them operate efficiently during both low and high wind , power electronics is used in modern wind turbines. However, due to the nature of the power electronics, harmonics are injected in the grid. In this work, the problem of high frequency noise injected by wind turbines to a local distribution grid is studied. The case study is conducted on a distribution grid placed in G tene kommun and owned by G tene Elf rening. At this particular grid, a high number of wind turbines are installed; where 29 wind turbines are producing the total amount of MW.

10 This study includes measurements and evaluation of the high frequency noise in the grid. The aim of this thesis is to study power quality issues caused by wind turbines. Furthermore, the thesis discusses the means of mitigations used to increase the power quality. The wind turbines in this particular grid are 4 quite spread out and measurements on all points of connections is not possible. For that reason, a part of the grid with particularly high density of wind turbines is chosen for the study. Purpose of the study The purpose of this study is to measure the high frequency noise in G tene elf renings grid injected by wind turbines. Furthermore, to study how it propagates and how the propagation itself affects the nose level. The purpose is also to investigate if the chosen method is adequate to evaluate the noise level and if any means for harmonic mitigation are needed.