New protection scheme for maintaining coordination time interval among relay pairs in micro-grid by employing centralised master controller

Abstract

The penetration of distributed generators (DGs) of large capacities in micro-grid introduces a considerable difference of current seen by the relay, during faults in its primary and backup region. This leads to several issues with the protection system such as relay miscoordination, delay in relay operation or failure in the relay operation (blinding). This study discusses a methodology to solve such issues by identifying the current status of micro-grid configuration. The proposed method performs well by maintaining the coordination time interval (CTI) between the relays, irrespective of the source strength (weak or strong), the mode of operation of the micro-grid (islanded or grid connected) or the micro-grid configuration (radial or looped). The method proposes three curves with different settings in a single relay. A suitable algorithm has been developed to calculate the relay settings for all the three curves of each relay, well in advance and this program is made to run in the central master controller (MC). Thereafter, MC sends the settings of all relays through a reliable communication channel. The proposed relaying scheme provides desirable CTI margin as compared to conventional over current relay. The simulation results of the novel protection scheme are validated through hardware emulation.