Electrical power systems are highly nonlinear and dynamic in nature: circuit breakers are closing and opening, faults are being cleared, generation is varying in response to load demand, and the power systems are subjected to atmospheric disturbances, that is, light- ning. Assuming a given steady state, the system must settle to a new acceptable steady state in a short duration. Thus, the electromagnetic and electromechanical energy is constantly being redistributed in the power systems, among the system components. These energy exchanges cannot take place instantaneously, but take some time period which brings about the transient state. The energy statuses of the sources can also undergo changes and may subject the system to higher stresses resulting from increased currents and voltages.
The analysis of these excursions, for example, currents, volt- ages, speeds, frequency, torques, in the electrical systems is the main objective of transient analysis and simulation of transients in power systems.