Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
This thesis concerns how the power quality in the grid is affected by the connection of wind power plants. As things are at present, Fortum Distribution AB has a number of wind turbines and wind parks connected to the own grid. As the pressure on building and connecting additional wind power is increasing, so is also the interest of how the already existing wind power generation affects the power quality in the nearby distribution grids. The study is performed by direction of Fortum Distribution AB and is limited to the 10 kV/40 kV-grid in Bohuslän, Sweden. The methods for calculation of power quality are compared to the results of a number of measurements. Also, the power quality parameters flicker, harmonics, unbalance and voltage variations are compared to regulated limits.
Long term voltage variations and flicker emission levels have been calculated from simulation results obtained in PowerGrid and PSS®E at seven different locations where wind power plants are connected.
Partly from these calculations, four different points for measurements are selected. The calculation results are subsequently compared to measurement data from the four different locations. Besides flicker and long term voltage variations, the parameters harmonics, unbalance and short term voltage variations have been registered and analyzed. The largest wind park to be analyzed contains six turbines at 2.5 MW of marked power each, connected to the 40 kV-grid. The individual turbines to be analyzed generate a maximum of 0.75 MW each and are connected directly to the 10 kV-grid.
Measurement results are compared to limits regulated in AMP and ASP which contains instructions and demands for connecting different production plants to the Swedish power grid. The results indicate an overall good power quality, however the flicker emission level exceeds the limits in all points of measuring. The theoretical calculations have proven to give a good estimation of the reality, but the calculation methods always provide a lower level of flicker emission than there is in the reality.
This is because of a basic flicker level in the grid originating from other sources than the wind power plant.
The calculation of voltage variations tends to give higher values in the calculations than in reality.
This is partly a consequence of the tap changers in the transformers which keep the voltage a good level and partly a result of calculating for an extreme situation that never does occur during the measurements.
2009. , 92 p.