For the system shown in Figure 10.44, directional overcurrent relays are used at breakers B12, B21, B23, B32, B34, and B43. Overcurrent relays alone are used at \(\mathrm{B} 1\) and \(\mathrm{B} 4\).

(a) For a fault at \(\mathrm{P}_{1}\), which breakers do not operate? Which breakers should be coordinated? Repeat (a) for a fault at

(b) \(\mathrm{P}_{2}\),

(c) \(\mathrm{P}_{3}\).

(d) Explain how the system is protected against bus faults.

B1 1 B12 Load 11 P B21 2 B23 Load L2 B32 3 334 Load L3 P B43 4 B4 Load L4