Decompositional modelling and simulation of power system electromagnetic transients

Electromagnetic transients are usually caused by switching operations, faults and lightning surges in power systems. These co-ordinates (instantaneous values of currents and voltages) are very important for power system planning, particularly for the protection scheme design, insulation, co-ordination etc. Generally power system electromagnetic transients are described by a set of differential, algebraic and Boolean equations, which relate instantaneous values of currents and voltages between each other. These sets of equations are usually referred to as mathematical models of power system electromagnetic transients. Mathematical models of modern power system electromagnetic transients are characterised by high dimension; and include nonlinearities, originated by the effect of electromagnetic apparatus (e.g. transformers, reactors etc.), magnetic core saturation and by nonlinear resistivity of surge arresters and overvoltage limiters. Moreover, switching elements such as relays, thyristors valves etc. should also be presented adequately. Because of the above reasons, mathematical models of power system electromagnetic transients are rigid, that is these eigenvalues, or time constants are wide spread. Therefore an integration step usually has to be chosen much smaller then the interval of interest since it is determined by the least time constant. Thus, the computation of power system electromagnetic transients is a very extensive problem which can nevertheless be efficiently solved by using decomposition methods.