Analysis of an Advanced Compounding Strategy based on Reactive Power Flow Measurement in the Medium Voltage Network

As well known, the increased share of renewable energies has led to new challenges for the electrical power system in Germany. Since the majority of renewable generation units are installed in the lower voltage levels, problems of congestion and voltage deviation occur more often. Commonly, the Distribution System Operators in Germany take advantage of a reactive power support by decentralised energy resources to ensure static voltage stability. The drawback of the support of reactive power for static voltage stability is the increasing demand for inductive reactive power by the distribution network which has to be compensated by the connected high voltage network. Besides, the power losses rise as well because of the additional reactive power flows. Therefore, other methods for voltage regulation like the use of compounding strategies at transformer stations could be advantageous to prevent the violation of voltage limits. This paper compares four different strategies of controlling the on-load tap-changer of the HV/MV-transformers in distribution networks and the effects on voltage deviation and power losses. A special focus is given to an advanced compounding strategy which adapts the control profiles of the compounding strategy dependent on the reactive power flow at the transformer as a second input parameter.