Investigation of the sympathetic tripping problem in power systems with large penetrations of distributed generation

This study contains an investigation into sympathetic tripping - the undesirable disconnection of distributed generators (DGs) (in accordance with the recently-introduced G83/2 under voltage protection) when a network fault occurs in the vicinity of the DG and is not cleared quickly enough by the network protection (i.e. before the DG´s under voltage protection operates). An evaluation of the severity of and proposal of solutions to the problem of sympathetic tripping on a typical UK distribution power network is presented. An inverter model (as the majority of DGs will be inverter-interfaced) that characterises the fault response of the inverter and its associated protection functions has been developed for use in simulation through exhaustive laboratory testing of a commercially-available 3 kW inverter for DG application; the observed responses have been modelled and incorporated in a power system simulation package. It is shown, when using presently-adopted DG interface and network protection settings, that the risk of sympathetic tripping is high in several future scenarios. To mitigate this risk, the impact of modifying network protection settings is evaluated. This study has two key findings - determination of the conditions at which the risk of sympathetic tripping is high and evaluation of a technique to mitigate this risk.