Investigation of islanding operation in a small distribution network with small scale generation unit

Abstract

Since the storm Gudrun in 2005, overhead lines are being replaced by underground cables. However the transition to cables lead to appearance of overvoltages during islanding. In order to analyze the problem, a part of the distribution grid where the problems appeared, is studied. The study is performed in PSCAD where a simplified model of the grid is built. Simplifications are used for the modelling of the surrounding grid and the customers are represented with lumped constant impedance loads. However, the other components of the system, such as transformers, cables, OHLs and generators are modelled in detail. Different islanding scenarios are simulated based on possible faults in the system. The results are analysed to find what the source of overvoltages and what in uence the level of overvoltage. A loss of connection from the main grid to the local generator causes instabillity and result in over- or undervoltage. A solution is to disconnect all shunt capacitances at the local generation units and install a shunt reactor to compensate for the reactive power generation from the cables. The reactor is only required if the cables reactive power consumption is too high.