Secured zone 3 protection during stressed condition

Summary form only given. Maloperation of zone 3 element of distance relay during stressed system condition such as power swing, load encroachment or voltage stressed condition is one of the main reason of large disturbances in power systems. Improved protection technique for zone 3 can help to prevent such maloperation and thus more reliable power system can be envisaged. This paper proposes an algorithm that utilizes two new criteria; (i) the maximum value of the transient monitoring function obtained from three-phase currents and (ii) the phase angle of the positive-sequence impedance to support zone 3 of distance relay. The technique is tested for various power system events such as three-phase fault during power swing, load encroachment, voltage stressed condition and CT saturation during three-phase fault using data simulated through EMTDC/PSCAD in the IEEE 39-bus New England system. The simulation results show that zone 3 protection scheme using proposed technique can correctly discriminate three-phase fault from stressed system condition.