Predictive Analytic to Supervise Zone 1 of Distance Relay Using Synchrophasors

Distance relays are the workhorses of transmissi-online protection systems. But those close to the electrical center will pickup even during transient instability. To identify them, we introduce a new coordinate system with normalized minimum magnitude of positive-sequence voltage on the line (V(minpu)) as the y-coordinate and angular separation of positive-sequence voltage phasors at line terminals (δSR) as the x-coordinate. We show that in the δSR- V(minpu) plane, the electrical center has a strong separation from a three-phase fault and stable disturbances. Subsequently, we propose a combined out-of-step prediction and relay blocking scheme. It uses line-end phasor measurement unit inputs for detecting vulnerable relays and blocking their zone 1 trip for a limited time interval before ingression into zone 1. We also show that it is possible to detect a line fault during the block state and consequently rescind the block decision. Extension of the proposed scheme to zone 2 and zone 3 is also described. Simulations considering noisy data and round robin delays demonstrate efficacy of the proposal.