Protection Schemes for Maintaining the Coordination Time Interval Between the Relays in Micro grid

Abstract

Conventional power system alone cannot meet the ever growing needs of electrical power in the world in a reliable manner. Under these circumstances, large penetration of Dis- tributed generators in the distribution level of the power system network is a great boon to the consumers. Due to the penetration of distributed generators (DGs) of large ca- pacities, the difference of current seen by protective relays, during faults in their primary and backup regions is considerable. As a result, the settings of the relay curve suitable for its primary region, is not capable of tripping within the desired time during fault in its backup region. This could lead to several issues with the protection system such as relay miscoordination, delay in relay operation and also failure in the relay operation (blinding). This thesis discusses a methodology to solve such issues by identifying the current status of micro-grid confi guration. The proposed communication based method works well by maintaining the CTI between the relays, irrespective of the source strength (weak or strong), or during different mode of operation of the micro-grid (islanded or grid connected) as well as for different micro-grid con figuration (radial or looped). Even when fault current is less than the load current, the suggested scheme is able to trip within the desired time and provides proper relay coordination. The performance of the communication based relay coordination is validated by comparing the updated relay tripping time with conventional operating time of the relay. The proposed scheme has been emulated in hardware and the results have been validated with the simulation re- sults. The thesis also discusses a methodology to reduce the total tripping time of the relays and this is achieved by a linear programming algorithm running in the Central Master controller(MC) to coordinate the relays using IEEE Standard curves...