ABSTRACT
The transient state is defined as the operating state of a power system which is characterized by sudden changes in load or in the circuit conditions. The disturbances may include faults, switching events, as well as abrupt and significant changes in loading. Neglecting resistance and variations in speed results in the electrical torque becoming numerically equal to the terminal power. The equal area criterion can not be used directly in systems where three or more machines exist and the assumption of an “infinite” system is either completely wrong or where more accurate system representation is desired. It should be emphasized that the criterion used in both the two machine analysis and the multi-machine system is based upon the examination of the first swing of the machine angles. The most severe fault from the viewpoint of transient stability is a solid three-phase fault. Various methods of including the effects of saturation have been devised.
