Design and implementation of an adaptive relay based on curve-fitting technique for micro-grid protection

The micro-grid should operate in a well controlled manner both during grid connected and islanded mode. Also, micro-grid equipped with conventional overcurrent relays has protection issues during faults due to the difference in fault currents when micro-grid operation changes from one mode to the other. This paper proposes suitable relaying scheme based on curve-fitting technique for micro-grids and performs well without using any extensive communication facility. A new algorithm is developed to create large number of fault data for fitting the curve. The fitness of curve is accessed by measuring the value of coefficient R-squared value (R-2). More number of polynomials is added to improve the value of R-2. Results show that the actual tripping time of the relay is very close to desired tripping time by introducing more number of polynomials. Efficiency of the proposed method is evaluated by comparing with conventional over current relay. The protection logic of the curve-fit relay has been implemented on a TMS32F28377S micro-controller based hardware. A laboratory based experimental setup has been established to test the operational performance of curve-fit relay for a five bus system.