Considering Dynamic Interdependencies in Modeling Reactive Power Behavior of Distribution Grids

A high share of the increasing amount of renewably generated electrical energy is fed to distribution grids. Renewable energy facilities as well as new kinds of load lead to highly stressed distribution grids with corresponding reactive power demand. When evaluating voltages in the transmission system, the reactive power behavior of distribution grids has to be considered. We conduct investigations evaluating typical medium and low voltage grids with varying types of automated controls comparing static voltage dependent models to a dynamic model with load recovery in situations with high feed-in gradients. Using a bottom-up approach, the impact of individual load-and feed-in-behavior on the reactive power demand of distribution grids as well as interdependencies with tap-changing behavior of distribution transformers is evaluated. We consider interdependencies with distribution system operation as applied in smart grids using detailed dynamic simulations in the timeframe of a few to several minutes. Thus, we illustrate the rising importance of considering dynamic interdependencies in modeling reactive power behavior of smart grids.