Protection Method for Radial Distribution Systems With DG Using Local Voltage Measurements

This paper presents a voltage-based protection method for distribution systems with distributed generation (DG). Considering the fact that any system fault is associated with a voltage dip at the faulted line ends, a novel protection relay characteristic is formulated from an extensive analysis of voltage behavior during fault conditions. The proposed method is independent of type, size, and location of DG units, as well as grid-connected or islanded (stand-alone) mode of operation of the distribution system. Moreover, the method is communication-less and uses only the local voltage magnitude to determine the relay operating time, hence, a low-cost protection method is provided. A threshold voltage level is defined outside the nominal voltage range. However, if under a fault condition the voltage dip is still within the nominal range, a current starter is used to trigger the relay. The effectiveness of the proposed method is verified by several simulation tests carried out on low voltage (LV) and medium voltage (MV) distribution systems under different fault condition and DG size and location for grid-connected and islanded modes of operation. The simulation results show the protection method is selective with appropriate speed, and the protection settings are independent of the distribution system modes of operation.