Indian Journal of Science and Technology

Abstract

Objectives: This work seeks to present a new protective relay for short circuits in AC micro-grids, under different control strategies as well as in both grid-connected and islanded modes of operation. Methods/Statistical Analysis: An index test-bed which consists of two wind turbines as micro-sources and other requisite network elements is developed. From the dynamic short circuit analysis of the test-bed, the rules which govern interaction of four parameters are framed in fuzzy form. Using the framed rules, fuzzy logic controllers are designed for micro-source and feeder sub-relays. The hardware of each sub-relay is realized in SimPowerSystems using combinational logic components. Findings: Offline and online response tests of the proposed relay show that it generates logic 1 during short circuits and logic 0 during normal operating conditions in both grid-connected and islanded modes of operation of the micro-grid. The proposed relay also provides equivalent response under both voltage and reactive power control strategies. This is consistent with response of a reliable protective relay as reported in related literature. The proposed relay also supports plug-and-play and peer-to-peer requirements of micro-grids. Similar to digital relays reported in literature, the proposed relay is a departure from classical relays wherein protection is based on threshold of short circuit current. In the proposed relay, protection is based on parameters of micro-sources and feeders. Application/Improvements: The proposed relay finds use in providing protection for personnel and system against short circuit currents. It reliably protects against single line-to-ground, line-to-line and three-phase bolted short circuits. 

Keywords: Fuzzy, Micro-grids, Multivariable, Relay, Short Circuits