Reactive power flows and voltage issues in urban distribution and subtransmission networks

In the last years, several changes have been faced by the electrical power systems. Notably, reactive power flows are significantly changed causing voltage issues not only on the subtransmission and distribution networks (SN, DN) but also on the transmission network (TN). Indeed, the penetration of less flexible or not controllable generators, the decommissioning of large conventional plants, the wide installation of cable lines in urban areas and the near-unity power factor of the most recent appliances contributed to markedly increase the absorbed capacitive reactive power (Qc). This paper is focused on the SN and DN of European Urban areas where these aforementioned conditions can be increasingly found. The work presents an evaluation of the voltage increases and reactive power flows on a real urban SN. Assessing the behaviour of the network under one year of operation and some other notable cases, it has been found that HV cable capacitances are generally predominant in the reactive power balance and in voltage issues. In these cases, simple remedial actions, e.g. shunt reactors' installation at suitable HV network locations can effectively and economically solve the problems.