Investigation of voltage problems caused by PV distributed generation on the LV distribution grid

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Supervisor:
Dr. Farkas Csaba
Department of Electric Power Engineering

Renewable energy is playing nowadays a significant role in electric power generation. The use of solar panels is very promising, the domestic small-scale power stations could be connected to the public power network. The use of these systems have many positive consequences, but they also can cause problems. For example backfeed can cause overvoltage at some parts of the transformer area and network losses might also increase.

In this thesis I introduce network topologies, which are used in low voltage grids, like radial, loosely crocheted network. This part of the thesis also contains the load profiles of the households and other consumers, which appear in the low-voltage network.

Then I introduce the small-scale domestic power plants, including solar systems. Using a solar system has advantages and disadvantages as well. I overview the current state and conditions of system installation. Then I continue with the technical and economical conditions of a system which is connected to the grid. I show the steps of the photovoltaic system connection to the grid, and what kind of economical influence there are.

Because connecting a solar panel raises some question of power quality, I discuss the major types of network effects caused by solar systems, and the prescribed standard values. I also write about the devices and protections, which promote proper operation.

The second part of the thesis contains the results of computer simulations. The investigated network is a low voltage grid with 5 junctions, which contains solar systems. I examine the overvoltage caused by the solar panels, and decide the amount of solar panels that can be connected to the grid without exceeding the voltage limit. I also examine how the location of the solar system affects to the endterminal voltage.

Because the voltage sometimes is out of the tolerance band, it is necessary to create a regulatory mechanism, which helps to terminate the difference. The viewpoint during the voltage regulation is that the voltage of the furthest point does not fall under the specified limits. I used stage control to voltage regulation which is installed on the MV / LV transformer. By the stage control the voltage was kept in the tolerance band.

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