Performance Enhancement of Overcurrent Relay in Distribution Systems by Extending Stability Limits and Considering High-Impedance-Fault

The electric power distribution scheme of a power plant should be analysed to prevent the occurrence of the slightest fault current and improve system reliability during the power production process. Protection relay settings installed on the electricity network should calculate the condition of the generator with various types of fault currents. Installation of relays that do not consider transient stability leads to generator instability even though the fault is eliminated. Therefore, it is necessary to calculate the stability limit while setting the overcurrent relay. However, a failure in the relay setting can occur if the inverse relay cannot protect against a high-impedance fault. Therefore, a method was proposed to determine the stability limit based on a short circuit without impedance and with an applied impedance, and the application of the method was demonstrated through existing settings and resetting conditions in simulation software. A modification relay setting prevented the loss of synchronisation of the generator during fault occurrence. The working time operation was integrated with the definite and inverse overcurrent relays in ANSI 50, 51, standard operating time of the relay, and critical clearing time of the generator. The type of fault used was a three-phase fault, with and without high-impedance. The calculation results demonstrated that this concept can be used to protect lines and generators during a short circuit current.