PROBLEM: A three-phase distance protection unit is used to protect a transmission line. This protection unit is composed

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Problem A Three Phase Distance Protection Unit Is Used To Protect A Transmission Line This Protection Unit Is Composed 1 (88.64 KiB) Viewed 96 times

PROBLEM: A three-phase distance protection unit is used to protect a transmission line. This protection unit is composed of SIX distance relays; 3 relays for phase faults (Rab, Rbc, Rca) and 3 relays for ground faults (Rag, Rbg, Rcg). Each of the 6 relays is a 3-zone directional impedance relay with the following settings: Zr1 = 0.3+j3 12 (Instantaneous), Zr2 = 0.45+j4.522 (0.25 s), Zr3 = 0.8+j8 2 (0.5 s). The compensation factor for ground relays is m=2.0. A B-C fault has occurred on the line. The resulting fault currents and voltages seen by the distance protection unit are: la = 0, Ib = -Ic=15.3 A /-175°, Vag = 80 V /0°, Vbg = 74 V /237°, Vcg= 73 V/123 (a) Calculate the impedance seen by each of the six relays. Draw the 3-zone characteristics of the relay and locate the calculated impedances on the characteristics. (b) What will be the response of each of the six relays (Block/ Trip (delay=?)). C) Comment on the performance of these distance relays. Explanations: If there is a phase-to-phase fault between Similarly, for a phase to ground fault on phase x, phases x and y such that x +y; measured fault impedance: and xy = a,b,c, then it can be shown that (Ix + m xlo) (Ix-ly) top (f/1s)0.02-1 where Zi is the positive sequence impedance of the entire line. (Ex) Z8 = KZ1 0.14 x TDS Z; z-y = Ex-Ey) =kz