Whenever there is insulation failure of equipment in a power system or flashover of the lines initiated by a lightning stroke or accidental faulty operation of the system, a heavy symmetrical short circuit current flows in the system. The system must be protected against flow of that heavy short circuit currents by disconnecting the faulty part of the system by means of circuit breakers operated by protective relays. The main objective of fault analysis is to determine the fault level or the fault MVA at the fault location. This fault MVA is the breaking capacity of the circuit breaker that has to be kept at the point of fault location.<\/p>\n
There are two types of fault occurring in the power system, namely \u201csymmetrical fault\u201d and \u201cunsymmetrical fault\u201d. The majority of fault occurring in power system are faults involving one line to ground occasionally two lines to ground which are termed as \u201cunsymmetrical fault\u201d. The faults involving all the three phase to ground or all the three phase short-circuited belongs to \u201csymmetrical fault\u201d. The symmetrical faults generally leads to most severe fault current which need to be interrupted. Though the operating conditions at the time of fault are important, the loads can be neglected during fault, as voltage dip very low so that currents drawn by loads can be neglected in comparison to fault current. The most common and dangerous fault, that occur in a power system, is the short circuit or shunt faults which involves power conductor or conductors-to-ground or short-circuit between conductors and causes a heavy current, called the \u201cshort-circuit current\u201d. Short circuit calculation is very important since they provide data, which is necessarily required for designing the protective scheme for the power system.\u201d<\/p>\n