(Solved): PROBLEM 1 [30pts]: A three-phase distance protection unit is used to protect ...

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PROBLEM 1 [30pts]: 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: \( \mathrm{Zr} 1=0.3+\mathrm{j} 3 \Omega \) (Instantaneous), \( \mathrm{Zr} 2=0.45+\mathrm{j} 4.5 \Omega \) \( (0.25 \mathrm{~s}), \mathrm{Zr} 3=0.8+\mathrm{j} 8 \Omega(0.5 \mathrm{~s}) \). The compensation factor for ground relays is \( \mathrm{m}=2.0 \). A B-C fault has occurred on the line. The resulting fault currents and voltages seen by the distance protection unit are: \( \mathrm{Ia}=0, \mathrm{Ib}=-\mathrm{Ic}=15.3 \mathrm{~A} /-175^{\circ}, \mathrm{Vag}=80 \mathrm{~V} / 0^{\circ}, \mathrm{Vbg}=74 \mathrm{~V} / 237^{\circ}, \mathrm{Vcg}= \) \( 73 \mathrm{~V} / 123^{\circ} \) (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) ii) What will be the response of each of the six relays (Block / Trip (delay=?)). (c) iii) Comment on the performance of these distance relays.