In this paper, affect of the wind turbines to power quality in weak grid is described to analyze wind turbines cooperation with weak gird. During the implementation of this study, number of power quality measurement series was carried through in L??tsa 35/10 kV substation on Saaremaa island. On the first time the wind park consisted three 500 kW synchronous wind turbines connected to the L??tsa substation. Second measurements were made, when there was already six 500 kW wind turbines with total capacity up to 3 MW. During the measurements approximately 310 hours of analysed material was collected, involving full and part-time operation time and total outage of all wind turbines. Possible impact of wind turbines to power quality in 10 kV and 35 kV power grid was controlled and analysed and the results compared to standards EVS-EN 50160:2000 “Voltage characteristics of electricity supplied by public distribution systems” and Eesti Energia’s company standard EE 10421629 ST 7:2001.
On the basis of measured results it can be concluded that at times there are moderate deviations from average voltage quality including brief emersions from the limits set in the standard at investigated substation. The analysis shows that limiting values of rapid voltage changes given in standard was frequently exceeded in comparison to contractual supply voltage. Permitted maximum value in an hour was exceeded several times. Also, large values of flicker,voltage and current harmonics factor have been noted during measured period.