Adaptive Impedance RelaywithComposite PolarizingVoltage

Fault resistance canbring somedisadvantages foran impedance relay whileasingle-phase-to-ground fault occurs on transmission line. Takingadvantage ofthecompensated voltage changing withfault resistance, thispaperpresents a kindof adaptive impedance relay withcomposite polarizing voltage to enhance thecapability against fault resistance. Ontheother hand, theoperating boundaryoftheadaptive relaymay enterinto "in-phase" region alongwiththeincrease offault resistance. To prevent theadaptive relay fromthe"in-phase" problem, anew additional blocking component isproposed inthis paper. Boththeadaptive relay andtheblocking component areall analyzed in thevoltage planeand theimpedance plane. Theoretical analyses showthatbothofthemhavecircular characteristics withgreater resistive tolerance. Theperformance oftherelay hasbeendemonstrated onatwo-source 500kmline 750kVsystem. IndexTermsdistance relay, highresistance, mhorelay, protective relaying