Fuzzy adaptive setting for time-current-voltage based overcurrent relays in distribution systems

In this paper an adaptive protection system based on the Fuzzy Logic for the adjustment of the overcurrent relay's pick-up currents with instantaneous and current-voltage based inverse-time units is proposed. In the methodology two variables are taken into consideration: the pre-fault current and the variation of current, which define various classes of the pick-up currents. This characteristic gives an adaptive behavior in the sense of accepting modified actuation curves. The framework for modeling and simulation was the Alternative Transients Program - The Electromagnetic Transients Program (ATP-EMTP). Due to the flexibility provided by the method, which allows the incorporation of new logic or changes on decision making, it resulted in an adaptive method that presented good performance by automatically following changes on the system operation condition and increased the sensitivity of the overcurrent protection. Tests with different short-circuit impedance in a distribution system with Distributed Generator (DG) have been carried out.