Neutral grounding in middle voltage power systems: Simulation model

In middle voltage networks in Croatia there are four neutral earthing concepts: isolated neutral point, low-impedance grounded networks, resonant grounded networks and networks with partial compensation. The paper will generally discuss modelling and simulation software developed for analysis of four grounding concepts mentioned earlier. Model was made using Matlab. Real time simulations were performed to test the behavior of middle voltage networks with different grounding concepts in case when single phase earth faults occur. The manner in which neutral point is treated has a fundamental influence on the value of the current and on overvoltages. The paper will also discuss influences that cable network connected to middle voltage side of network transformer and the moment when a fault occurs have on the value of the current and on overvoltages. Based on the simulation results, the paper presents the possibilities and limitations of various neutral earthing concepts in medium voltage systems.