Situation
One of the largest photovoltaic power plants with a peak power of 5-MWp has been erected in Espenhain, approx. 20 km south of Leipzig, Germany. GEOSOL Gesellschaft für Solarenergie mbH, Shell Solar GmbH and WestFonds Immobilien-Anlagengesellschaft mbH constructed the "Solarpark Leipziger Land" on a disused coal dust landfill. It stands in an approximately 22-hectar coal dust settling basin created by more than 40 years of lignite mining. By erecting a photovoltaic power plant, it has been possible to put the site to an economic and meaningful use. Siemens was the general contractor for the technical equipment.

Problem
The plan was to collect the photovoltaic power with SINVERT central inverters and feed it compatibly into envia's 20-kV system. Moreover, the auxiliary power supply drawn through a separate 400-V system link had to comply with the voltage quality and personal safety requirements. A technical and economic system and protection concept and the dimensioning of all equipment had to be worked out for the entire photovoltaic power plant.

Solution
We analyzed the network requirements of the central inverters and developed a 20-kV and 400-V system concept. The transformers, cables, 20-kV substation, and protection devices were technically and economically optimized and dimensioned based on load flow and short-circuit calculations, and the short-circuit strength of these equipment items, selective protective setting and personal safety were verified.
We drew up a report based on the German BDEW guidelines for the system compatibility at the 20-kV tie point. We did this by testing the system connection conditions, power integration, voltage rise, short-circuit stress, voltage rise caused by switching, voltage fluctuation, harmonics, interference voltages, and disturbances to the audio-frequency ripple control systems.

Overview