In the figure below, a three-phase, 1000-kVA, 480-V, Y-connected generator with ungrounded neutral has armature resistance R_a = 1% and subtransient reactance Xʺ_d = 10%. It feeds a three-phase, 75-kVA, 480/208-V transformer with R = 1% and X = 5%. The cable has R = 0.08 Ω and X = 0.026 Ω per phase per 1000 ft. For an L-L-L fault with no ground involved, 150 ft. away from the transformer terminals, determine the symmetrical rms value and the first offset peak of the fault current in a 150-ft. cable. Repeat the calculations to determine the circuit breaker fault current rating on the 75-kVA transformer secondary terminals.

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Gen 1000 KVA, 3-ph, 480-V, ungrounded 1 + j10% 75-kVA, 3-ph, 480/208 V, Z = 1 + j5% 150-ft. cable ell ell CB L-L-L fault 480-V loads 120-V loads