Exact Calculation of Simultaneous Faults Involving Open Conductors and Line-to-Ground Short Circuits on Inherently Unbalanced Power Systems

The analysis of simultaneous faults, espec ially involving mutually coupled lines on inherently unbalanced power systems using the symmetrical components technique, may not be practically feasible because of the difficulties encountered in the assembly f sequence networks and their solution. To al-le- these problems, this paper presents an alternative method for digitally simulating a basically ubnlanced three-phase power system which is subjected to a shunt fault at one location and blown fuses or open conductors at another location. The method involves phase frame representation of network elements and the use of the distributed source solution technique in conjunction with the principle of superposition. e phase coordinate model of power system ele- is modified/enlarged to simulate inherent system imbalances as well as the unbalancing contributed by the change in network configuration. The unbalance conditioned by large single-phase loads, untransposed transmission lines, conductor bundles, etc. is re- flected in the polyphase admittance matrix. Consequently, line removals, additions, impedance changes, conductor and phase openings can be simulated quite easily by simply modifying the base case admittance matrix. Even the treatment of mutually coupled lines presents no computational problems, unlike the symmetrical component approach. Thus, the proposed method makes it possible to analyze simultaneous faults on basically unbalanced power systems with the same ease and simplicity as unsymmetrical faults on a balanced system with the aid of symmetrical components. The method is applicable to any combination of series and shunt faults occurring anywhere in the system.