Distance protection for smart grids with massive generation from renewable sources

It is widely known that Distributed Generation (DG) changes the radial operation of the most common distribution systems. Actually, the system is no longer passive but it becomes active, and bidirectional power flows can appear on the distribution network. In this condition, also the fault currents may be drastically changed causing problems to the protection system, which normally uses overcurrent protection devices in radial distribution circuits. In order to solve this problem, a new protection procedure is proposed, based on distance protection concepts and synchronization of the voltage and current samples coming from the two terminals of the faulted MV line segment. The method involves the circuit equations in the time-domain, and the fault identification algorithm exploits the Recursive Least Square approach. A thorough set of Matlab simulations are carried out, in order to validate the proposed algorithm, which exhibits good performances also in case of high distortion of the acquired voltage and current waveforms. Indeed, it reveals to be robust, precise and very fast. Moreover, the algorithm provides, by product, a very good estimate of the fault resistance so it correctly works also in presence of high fault resistances that can occur in the herein considered distribution systems