Optimal Reach Settings of Mho Relay for Series Compensated Transmission Line Protection

In three-phase series compensated long transmission line, when the fault occurs in the system, the parameters like capacitive reactance $(\mathrm{X}_{\mathrm{c}})$ and fault reactance $(\mathrm{R}_{\mathrm{f}})$ can cause the distance relay to either under reach or over reach. This parameter can cause error in the estimation of fault impedance, vhere it gives apparent impedance due to vhich exact fault location cannot be determined and due to this the relay mal operates. To avoid mal-operation of distance relay, many filtering techniques like discrete Fourier transform (DFT), fast Fourier transform (FFt), wavelet filter, cosine filter, and prony filter are usedL This article deals with the best possible reach setting for the functional characteristics of the three-phase series compensated with trans mission line. Prony method remains as the baest alternative to acquire the accurate impedance calculated by measuring the voltage and current frequency phasors.