Envelope based symmetrical fault detection during power swing for series compensated lines

Reliability of the power system can be sustained with a distance relay function of accurate tripping signal. Blocking the relay during a power swing and unblocking with the occurrence of a fault can ensure this function. A fault detection technique is required to achieve blocking and unblocking conditions. Detection of the fault is difficult during a power swing, even more challenging with series compensation due to nonlinear functioning components such as thyristor-controlled reactor and metal oxide varistor. By considering different states of the power system, a new approach is proposed for transmission lines to detect fault during power swing. The proposed technique is based on observation of envelopes defined by local maxima values and uses DC offset current and fifth harmonic values as main parameters. The DC offset voltage and a reactive power tracker are added to provide high accuracy with both fixed and thyristor-controlled series compensation. The proposed method focuses on symmetrical faults. Performance of the proposed technique is presented and verified with a two machine test system. The method is also tested and compared in detail with Western system coordinating council three machine nine bus system by varying selected system parameters.