The CT ratio and PT ratio to protect a line are 240 and 2000, respectively. If the impedance of each line is 10 ohm. What is the relay impedance to protect the line from fault. a. 83.33 ohm b. 1.2 ohm c. 48,000 ohm d. 12 ohm

b) A fault occurs at bus 3 of the network shown in Figure Q4. Pre-fault nodal voltages throughout the network are of 1 p.u. and the impedance of the electric arc is neglected. Sequence impedance parameters of the generator, transmission lines, transformer and load are given in Figure Q4. V₁ = 120° p.u. V₂ = 120° p.u. V₂ = 1/0° p.u. V₂= 120° p.u. jXj0.1 p.u. JX2) 0.1 p.u. jX0j0.15 p.u. jXn-j0.2 p.u. 1 JX(2)-j0.2 p.u. 2 jX)=j0.25 p.u. JX20-10.15 p.u. jXa(z)-j0.2 p.u. 4 jX2(0)=j0.2 p.u. jXT(1) j0.1 p.u. jXT(2)=j0.15 p.u. jXT(0)=j0.1 p.u. Figure Q4. Circuit for problem 4b). = jXj0.1 p.u. j0.1 p.u. - JX(2) JXL(0) 10.1 p.u. = (i) Assuming a balanced excitation, draw the positive, negative and zero sequence Thévenin equivalent circuits as seen from bus 3. (ii) Determine the positive sequence fault current for the case when a three- phase-to-ground fault occurs at bus 3 of the network. (iii) Determine the short-circuit fault current for the case when a one-phase- to-ground fault occurs at bus…

Q1. The following figure shows the differential protection of power transformers with specifications of 20 MVA, 66/11 KV.Trans is No load.If a two-phase short circuit occurs between phases b and ¢ It is desirable to calculate the currents passing through the CTs and relays R, Y, B. If these relays are three overcurrent relays with inverse characteristics as T=0.63 / log (I / Iset) and Iset =0.5A.Will this work for short circuit relays? If yes, which relay works faster and at what time?

In the following network, the voltage magnitudes at all buses are equal to 1 p.u., the voltage phase angles are very small, and the line resistances are negligible. All the line reactances are equal to j1 p.u. (1) (2. P₂ = 0.1 p.u. P3 = 0.2 p.u. The voltage phase angle 83 in radian at bus 3 is (Assume one of the generator bus as slack bus and sin-¹ (0.1) = 0.1 rad) (a) -0.1 (b) -0.2 (c) 0.1 (d) 0