Determining the Sufficiency of Standard Protective Relaying for Islanding Prevention in Grid-connected Pv Systems

'\B:,TRAC r· Recently there has been a resurgence of conccrn about islanding of grid-connected photovoltaic (PY) ,ystems rhis condition occurs when the PY system continues to energize a section of the grid after that section has been Isollted from thc main utility voltage source. Generally, islanding is undesirable for a number of reasons, and it is therefore important that PY systems incorporate methods to prevent islanding. However, PY systems are in general already required to be equippcd with standard protective relays, namely over/undervoltage relays (OYR/UYR) and over/underfrequency rclays (OFRJUFRl, which disconnect the PY system from the utility system in the event that either the magnitude or Irequency of the PY system's terminal voltage deviates beyond certain Ihresholds. These relays will prevent islanding in the majllrity of cases. In fact, it has been argued that the probability of an islanding event that would not be detected by these relaYs is insignificant. The purpose of this paper is to investigate the probability of occurrence of the conditions which could lead 10 failure of the OVRlUVR and OFRlUFR to detect islanding using three methods, and thereby to detennine whtther the standard protective relays provide sufficient islanding protection.