Overcurrent relay setting by using adaptive technique

Abstract

As cost-effective protection relays, Overcurrent (OC) relays are used as the main protection equipment in distribution grids and backup protection for distance relays in transmission and sub-transmission lines. Basically, two parameters are considered as OC relays settings: pickup currents ( Ipick up ) and Time Setting Multiplier (TSM). Hence, the objective in the coordination problem o f OC relays is to determine Ipick up and TSM of each relay. These methods can be classified into two different approaches: Off-line and On-line coordination approaches. By analyzing all faults, abnormal operating conditions, and system contingencies as well-known as Off-line coordination techniques, several methods have been developed to solve coordination problem o f OC relays. However, the response of relays would not be satisfactory in a condition which has not been included the analysis earlier. Meaning that, required short circuit currents due to any fault that occurred in grid cannot be adjusted to the coordination problem of OC relays. Therefore, the risk of occurring mal-operation or miss-coordination becomes high. In order to achieve a robust protection scheme, the OC relays settings must be updated regarding to any change which results into new topology of the grid. In this thesis, a reliable protection scheme is achieved by implementing the proposed adaptive protection algorithm. For this purpose, the idea of employing the Thevenin equivalent circuit is utilized to check the power grid operation for any change continuously. By applying the proposed technique, the accurate settings of overcurrent relays in distribution network are determined. As a result, the proposed adaptive protection algorithm can avoid the unnecessary blackouts in distribution network and provide reliable and sensitive protection scheme.