Värmning av avloppsvatten med spillvärme för att förbättra kvävereningen -Temperaturens inverkan på kvävereningen
The goal for this master thesis project has been to investigate the power quality in adistribution grid, which has a high fraction of dispersed power production due towindmills. The study has been done on a grid in Laholm South of Halmstad, whereapproximately 45 windmills are connected to the distribution grid owned by SHKEnergi. The investigation has been focused on to two radialy fed 20 kV lines, wheretwelve windmills are connected.Voltage variations have been studied by creating a model of the grid in the simulationprogram SIMPOW. The largest deviation that has been found in any point of the gridis ±1.9 % of the nominal voltage. This deviation is a result of varying powergeneration from the windmills and the voltage regulation at the connection point ofthe 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 usingcalculations based on flicker coefficients obtained from the windmill manufactures.The highest flicker emission calculated is 0.15 and occurs during repeated switchingof the windmill to the grid. This result is somewhat uncertain, but it is far from thelimit of 0.25. The flicker emissions from the windmills should therefor not cause toomuch disturbance.Measurements on the low-voltage side at a station on one of the 20 kV lines verify thegeneral 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 kVvoltage together with lines with large conducting area makes up a strong grid.