PROTECTION OF TRANSMISSION LINES USING PMUs DURING SEVERE STRESS CONDITIONS

Abstract

The third zone protection element of distance relays may malfunction during stressed sys- tem conditions, such as load encroachment, power swing and voltage stressed condition, leading to large and severe disturbances in power systems. Two algorithms for improved and robust zone 3 protection provided by a distance relay have been discussed here. The rst algorithm, which is the TMF based algorithm, helps in discriminating a three phase fault from a stressed condition by making use of the phase angle of the positive-sequence impedance measured by the relay and the maximum value of the transient monitoring function. This technique has been tested for three cases: power swing condition, voltage stressed condition and during load encroachment on the IEEE 39-bus New-England system. The results show that the third zone protection provided by a distance relay using this algorithm helps in successfully discriminating three phase fault from stressed system conditions. The FZC based algorithm attempts to detect a power swing condition and identify it as a stable or an unstable swing by using the rst zero crossing concept. It makes use of only the local measurements of voltage and current as provided by a PMU. This algorithm has been simulated on a simple three bus system and a modi ed WSCC 9-bus system. The simulation results show that the algorithm can immediately identify a power swing as stable and hence can help in sending a blocking signal to the relay to prevent its maloperation. The simulations have been carried out in PSCAD v4.5 software and the calculations and plots have been obtained by making use of MATLAB 2014a software.