Risk assessment of unintentional islanding in a spot network with roof-top photovoltaic system — A case study in India

Grid-connected Photovoltaic (PV) systems, when produce power comparable to local demand, pose a risk of sustained operation in islanded mode unintentionally. This paper presents a case study to assess the probable scenarios of unintentional islanding in a spot network with roof-top PV system. Most probable time slots during which the unintentional islanding can sustain are identified based on the permissible deviations in operating voltage of the distribution network which in turn can be represented as an allowable mismatch between demand and supply of real and reactive power. 3-Φ Distribution Power Flow (DPF) has been used to verify the steady state equilibrium between demand and supply of real and reactive power from the local resources present in the network under investigation during its operation in islanded mode. The exercise is based on the metered measurements of local demand and PV generation for the period of six months at half hourly intervals. The outcome of the risk assessment exercise identifies the time-slots in terms of likely days and likely time of day when islanded operation may continue to energize the distribution network for longer than couple of seconds. Results can help reorganize maintenance or network expansion activities in order to minimize the risk of unintended islanding.