POSTER PAPER International Journal of Recent Trends in Engineering, Vol. 1, No. 4, May 2009 8 Effect of Wind Speed Changes on Grid Power Quality at Various Levels of Wind Electric Penetration -A Laboratory Investigation V.Vanitha 1 and Dr.N.Devarajan 2 1 Amrita School of Engineering/ Electrical and Electronics Engineering,Coimbatore,India Email:v_vanitha@ettimadai.amrita.edu 2 Government College of Technology/Electrical and Electronics Engineering,Coimbatore,India Email:profdevarajan@yahoo.com Abstract: This paper presents a laboratory study of the effect of wind speed changes on grid power quality parameters such as voltage, frequency, power factor and harmonics at different penetration levels of grid connected wind electric generator (WEG). Linear and gust changes of wind speed are considered in the analysis besides a constant value. The analysis is done on a three phase squirrel cage induction generator (SCIG) coupled to a DC shunt motor in the laboratory. The wind speed change is simulated as a shaft speed change of SCIG. The effects on power quality at various levels of penetration and different types of speed change are compared. Results obtained are compared with field datas and simulation results. Index Terms: Induction generator, real and reactive power, power factor, voltage, frequency, harmonics I. INTRODUCTION Recently wind power generation has been experiencing a rapid development in a global scale. Grid-connected wind turbines of the first generation were relatively small and their impact on the grid was also small; therefore any disturbance within or created by the wind plant was negligible. But today, a large amount of wind power is integrated to the power system and these have potential to be an increasing threat to the stability and power quality of the grid to which these are connected[2]. Many power quality improvement techniques have been developed nowadays[3][4].Since long, the squirrel cage induction generator has been the mostly used type of generator for wind turbines. The machine always requires reactive power and it varies with active power. Fig.1 shows the grid connected wind electric power generation scheme. The power captured by wind turbine is converted into electrical power by induction generator and is transmitted to grid. To be in the generating mode, the squirrel cage induction generator (SCIG) should be driven by the turbine at a super- synchronous speed(i.e)at negative slip. Simulation results for power quality of grid with wind electric generators have been dealt in many papers[1][3][4][5][7]. Here the experimental results and field results for the same are presented and discussed. II. LABORATORY SIMULATION OF THE SCHEME In the experimental set up developed for the study, a DC shunt motor is used as the prime mover for SCIG. Output power of a wind turbine increases with increase in wind speed; to absorb this increased power input to SCIG, the latter has to run at increased shaft speed. Therefore, the wind speed change is simulated as the shaft speed change of the DC(Direct Current) motor coupled mechanically to the SCIG. Speed control of DC motor is done using field control method. Fig.2 shows the diagram of the experimental set up. The laboratory simulation also includes a transmission line model and a conventional electric power source. In order to vary the penetration level of the WEG, three different power sources have been used, namely, (i) the original 22 kV power utility grid, (ii) a 250 kVA diesel generator and (iii) a 5 kVA alternator with a DC motor drive. Case 1: When it is connected through LT(Low Tension) feeder to a bus energized from a 22 kV substation linked to large transmission network Case 2: When it is connected to a bus energized from a 250 kVA, 400 V diesel generator Case 3: When it is connected through transmission line model to a 5 kVA alternator The penetration level of WEG progressively increases from Case 1 to Case 3.In each case, studies are carried out for three different wind speed profiles (i) constant wind speed, (ii) linearly changing wind speed and (iii) gust. Fig.1. Grid connected wind electric generation scheme Fig .2. Diagram of experimental set up III. EXPERIMENTAL RESULTS Case 1: SCIG connected to the large power grid (Low penetration level) © 2009 ACADEMY PUBLISHER