Impact of distributed energy resources on the low voltage distribution network
E.On Czech Republic
The supply territory of the E.ON Distribution in the Czech Republic, operated by the company E.ON Czech Republic, accounts for approximately 1.5 million customers. The most of them are supplied from the low voltage (LV) distribution network. More than 1000 MW of distributed energy resources (DER) were connected to E.ON network in Czech Republic mainly in photovoltaic (PV) sources. The mass operation of generating plants also results in poorer voltage quality parameters in the distribution network. In case of accumulation of sources in one part of distribution system, it is possible that overvoltage will be detected or else voltage variations will not comply with the requirements of the standard EN 50160. The theoretical impact of DER on voltage quality has already been described. Practical experience of the operation of DER from the distribution network operator´s (DNO) side is not available or the measured data are not from the area E.ON Distribution or the measured data are not up-to-date. This paper brings a current study of VQ measurements which were carried out in year 2016.
Thirty other representative LV distribution grids with connected PV plants were chosen and these grids were measured. Each measurement lasted at least one week according to the EN 50 160 standard. Two VQ measurements were made at the same time in each grid, first in the substation (on the LV level, on the output of the transformer 22kV/0.4kV) and second in the point of connection of PV plant to LV distribution grid (supply terminal of PV plant). All the VQ measurements were evaluated with the focus on voltage variations, flicker, voltage unbalance and voltage harmonics.
The question is when the DNO and when the customer is responsible for poor VQ. It can be used the reference impedance according to the standard IEC 60725 as the guideline for decision about responsibility for poor VQ. In this paper the real short circuit impedance was measured and compared with the reference value for each grid.