Immunity Improvement of a Low-Impedance Restricted Earth Fault Relay by Making its Mechanism Intelligent based on Support Vector Machine

Low-impedance Restricted Earth Fault (REF) relay is a unit of digital protection system of power transformers that its duty is detecting single phase to ground faults on the transformer terminal and turning it to core faults on its windings. It is a fast and sensitive type of protection schemes. However, during external fault with high magnitude fault currents and flowing magnetizing inrush current of power transformer, due to Current Transformer (CT) saturation, it may be exposed to maloperation. In this paper, immunity improvement of a REF relay is shown by making its algorithm intelligent. To do so, in the first step, major parameters used in the operating characteristic of a conventional REF relay and neutral current are chosen to be employed as the training input of Support Vector Machine (SVM) classifier. Then, a sample power system including a power transformer and related CTs is simulated by using PSCAD/EMTDC software under many different operating conditions involving internal fault, external fault, and inrush current. Finally, support vector machine is trained using obtained simulation results and after validating its accuracy, is employed as the intelligent core of the new REF protection scheme.