Islanding detection method of distributed generation units connected to power distribution system

In this paper, as an active technique for detecting the islanding, voltage magnitude variation method of distributed generation (DG) unit is proposed. The proposed new algorithm detects the islanding by distinguishing the differences in the system characteristic between those experienced when the DG unit is running in parallel with the utility supply and when it is operating independently. In the parallel operation mode, due to the high capacity of the utility system, any change in the voltage magnitude of DG unit produces smaller change in the voltage at the inter-tie point than that in islanding operation mode, and larger change in the injecting reactive power at the inter-tie point than that in islanding operation mode. That is, when the small change on the voltage magnitude of DG unit is made within 0.01 per unit, if the voltage at the inter-tie point changes as much as the small change and the injecting reactive power at the inter-tie point has almost no change, that operation state can be decided to be islanding operation mode. This proposed method is proved through computer simulations.