Three-zone mho relays are used for transmission line protection of the power system shown in Figure 10.25. Positive-sequence line impedances are given as follows.

Rated voltage for the high-voltage buses is \(500 \mathrm{kV}\). Assume a 1500:5 CT ratio and a 4500:1 VT ratio at B12.

(a) Determine the settings \(Z_{t 1}, Z_{t 2}\), and \(Z_{t 3}\) for the mho relay at B12.

(b) Maximum current for line 1-2 under emergency loading conditions is \(1400 \mathrm{~A}\) at 0.90 power factor lagging. Verify that B12 does not trip during emergency loading conditions.

Data From Figure 10.25:-

Transcribed Image Text:

Line Positive-Sequence Impedance, 1-2 6+j60 2-3 4+j40 2-4 5+j50