Sensitivity and stability analysis of loss of main protection in active distribution networks

Due to the significant increase in the market penetration of low inertia Distributed Generation (DG) systems recently, the power flow in typical distribution systems has changed, causing an adverse impact on power system operation & protection. The performance of power system protection at a distribution level is becoming increasingly critical to the reliable operation and stability of the whole system. This paper presents a comparative analysis in terms of sensitivity and stability impact, on Loss-of-Mains/anti-islanding (LOM) protection between traditional generation types and inverter-based DGs. Three phase Synchronous Generators (SG) and Photovoltaic (PV) with active and reactive power (PQ) control were chosen for study and modelled in the PSCAD software. The designed system includes a Rate of Change of Frequency (ROCOF) relay, connected to a typical medium voltage UK distribution network. The impact of loss-of-grid and network disturbances on ROCOF performance has been analyzed and assessed. Based on evaluation of the simulation results, the paper also proposes the need of an adaptive setting approach to provide an optimum setting which compromises between sensitivity and stability.