General Fault Admittance Method Solution of a Line-to-Line Fault

In the classical approach, line-to-line faults are usually analysed using a parallel connection of symmetrical component sequence networks. The sequence networks are solved separately, and then the positive and negative sequence networks are connected in parallel for a line-to-line fault, and solved to obtain the phase quantities. The solution proceeds by identifying the connection of the sequence networks at the fault point and then solving for the symmetrical component currents and voltages. These are then used to determine the symmetrical component voltages at the other busbars and hence the symmetrical component currents in the lines. The approach requires that the connection of the sequence networks be known for the common fault types. However, a solution by the general method of fault admittance matrix does not require prior knowledge of how the sequence networks are connected. This makes the general method more versatile than the classical methods. The paper presents a procedure for simulating a short circuit, which is a requirement for using the general fault admittance method. A simple power system containing a delta earthed star transformer is analysed for a line-to-line fault. The results obtained are as accurate as those obtained using the classical approaches.