Technical Impacts of Overhead-Line to Underground-Cable Transition in Distribution Grids

Underground-cable (UC) systems are expected to substitute overhead lines (OVH) in the near future because of governmental policies and environmental concerns. Compared to OVH, due to being more capacitive and less resistive, UC systems tend to increase voltage magnitudes and short circuit currents all along the line. In addition, PV systems are also known to cause significant voltage rise problems in distribution grids. Assuming the combined dominance of UC and renewable energy systems in future power grids, new challenges are needed to be identified in advance. Existing and prospective problems should be revealed to better understand the dynamics behind them. Therefore, this study is divided into three parts. First, the case of complete transition from OVH to UC is technically analyzed in terms of voltage profiles and short circuit currents. Second, PV systems, as renewable energy sources, are attached to the problem. Then, the challenges associated with the combination of these two systems are identified. Third, to mitigate the voltage related problems, a two-stage strategy is proposed using shunt reactors and reactive power support capabilities of PV inverters. According to the simulation results, the proposed strategy can be a promising solution in dealing with the voltage variations and voltage unbalance problems.