నైరూప్య

Prevention of False Operation of Distance Relay in Ferroresonance

Salman Rezaei

Ferroresonance is one of the main causes of failures in electrical network. It results in increasing the magnitude of voltage and current, which causes operation of protective relays. Impedance measured by distance relay is deviated in effect of Ferroresonance; furthermore, swing behaviour of power and impedance in effect of Ferroresonance causes operation of OSB (Out of Step Blocking) element of distance relay; hence, operation of relay is blocked. In this paper, Ferroresonant states are examined in Manitoba Hydro 230 kV electrical network by means of PSCAD/EMTDC. Ferroresonance is detected by means of visual detection tools. Effect of Ferroresonance on distance relay and OSB element is analyzed. An adaptive Logical algorithm, which is based on THD (Total Harmonic Distortion) and Fr.d (Frequency deviation) measurement in time domain, is implemented in the software. Ferroresonant states are re-examined in presence of the logical algorithm in distance relay to prevent mal-operation of the relay; furthermore, stability domain boundary of voltage based on THD and frequency deviation is specified by the algorithm in the network.