The four-bus power system in Figure 2 has following equipment parameters: G1: 500 MVA 13.8 KV, xd"=x1=x2=0.20, x0=0.10pu G2: 750 MVA, 18 kv, xd"=x1=x2=0.18, x0=0.09pu G3: 1000 MVA, 20 kv, xd"=x1=0.17, x2=0.20, x0=0.09pu T1: 500 MVA, 13.8/500 kv, delta-wye, x=0.12pu T2: 750 MVA, 18/500 kv, delta-wye, x=0.10pu T3: 1000 MVA, 20/500 kv, delta-wye, x=0.10pu Each Line: X1 = 50 Ω; X0 = 150 Ω All per-unit reactance values are given on the respective equipment rating (voltage and power) as the base. The inductor connected to generator G3 neutral has a reactance of 0.028 Ω. (a) Draw the zero- positive- and negative-sequence reactance diagrams using a 1,000 MVA, 20 kV base in the zone of generator G3. Neglect ∆ - Y transformer phase shift. (b) Faults at bus 1 are of interest. Determine the Thevenin equivalent of each sequence network as viewed from the fault bus. Prefault voltage is 1.0 pu. Prefault load currents and ∆ - Y transformer phase shift are neglected.

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Fault Analysis

In an electrical engineering system, a fault is an abnormal electric current flowing through the system, and fault analysis is the study of these faults. For instance, a short-circuit is a fault where the live wire touches the ground or neutral wire. If a circuit is interrupted by a failure of a current-carrying wire then an open circuit fault occurs. The open-circuit faults are also called series faults. One or more phases or ground may be involved in a three-phase fault or may occur only between two phases. Current flows into the earth in case of a ground fault or earth fault. For most situations, the prospective short circuit current of a fault that is predictable can be calculated. To limit the loss of service because of a failure, the protective devices can detect fault conditions and operate circuit breakers and also other devices. All phases equally can be affected in a poly-phase system which is known as symmetric electrical fault. The asymmetric fault becomes more complicated to analyze if only some phases are affected. By using methods such as symmetrical components, the power system analysis of these types of faults is often simplified. The main objective of power system protection is to design, detect, and interrupt power system faults.