A simple system with circuit breaker-relay locations is shown in Figure 10.49. The six transmission-line circuit breakers are controlled by zone distance and directional relays, as shown in Figure 10.50. The three transmission lines have the same positive-sequence impedance of \(j 0.1\) per unit. The reaches for zones 1,2, and 3 are 80,120 , and \(250 \%\), respectively. Consider only three-phase faults.

(a) Find the settings \(Z_{\mathrm{r}}\) in per unit for all distance relays.

(b) Convert the settings in \(\Omega\) if the VTs are rated \(133 \mathrm{kV}: 115 \mathrm{~V}\) and the CTs are rated 400:5 A.

(c) For a fault at location X, which is \(10 \%\) down line TL31 from bus 3, discuss relay operations.

Transcribed Image Text:

G1 O 0.03 B4 T1 B1 1 B12 B13 TL13 X B31 3 TL12 TL23 Y B32 B21 B23 2 B2 T2 i itu 5 B5 0.03 G2