Undersökning av elkvalitet i distributionsnät med omfattande vindkraftselproduktion
Examensarbete för masterexamen
The goal for this master thesis project has been to investigate the power quality in a distribution grid, which has a high fraction of dispersed power production due to windmills. The study has been done on a grid in Laholm South of Halmstad, where approximately 45 windmills are connected to the distribution grid owned by SHK Energi. The investigation has been focused on to two radialy fed 20 kV lines, where twelve windmills are connected. Voltage variations have been studied by creating a model of the grid in the simulation program SIMPOW. The largest deviation that has been found in any point of the grid is ±1.9 % of the nominal voltage. This deviation is a result of varying power generation from the windmills and the voltage regulation at the connection point of the line. If load variations also are considered the largest voltage variation is ±2.4 %. The voltage variations should therefore not cause any real problems. The examination of flicker, which are fast voltage variations, has been done using calculations based on flicker coefficients obtained from the windmill manufactures. The highest flicker emission calculated is 0.15 and occurs during repeated switching of the windmill to the grid. This result is somewhat uncertain, but it is far from the limit of 0.25. The flicker emissions from the windmills should therefor not cause too much disturbance. Measurements on the low-voltage side at a station on one of the 20 kV lines verify the general impression that the power quality is good. The voltage variation is about ±2 % from nominal voltage while neglecting disturbances caused by a low-voltage load. The voltage distortion is far from the recommended 6 %, it highest value is only 1,11 % and it is most of the time below 1 %. The good power quality is a result of the modern and well-dimensioned grid. 20 kV voltage together with lines with large conducting area makes up a strong grid.
Elkraftteknik , Electric power engineering