TABLE OF CONTENTS The operation of an electrical power system involves continuous electromechanical and electromagnetic distribution of energy among the system components. During normal operation, under constant load and topology, these energy exchanges are not modelled explicitly and the system behaviour can be represented by voltage and current phasors in the frequency domain.
However, following switching events and system disturbances the energy exchanges subject the circuit components to higher stresses, resulting from excessive currents or voltage variations, the prediction of which is the main objective of power system transient simulation.
Figure 1.1 shows typical time frames for a full range of power system transients. The transients on the left of the figure involve predominantly interactions between the magnetic fields of inductances and the electric fields of capacitances in the system; they are referred to as electromagnetic transients. The transients on the right of the figure are mainly affected by interactions between the mechanical energy stored in the rotating machines and the electrical energy stored in the network; they are accordingly referred to as electromechanical transients. There is a grey area in the middle, namely the transient stability region, where both effects play a part and may need adequate representation.
In general the lightning stroke produces the highest voltage surges and thus determines the insulation levels. However at operating voltages of 400 kV and above, system generated overvoltages, such as those caused by the energisation of transmission lines, can often be the...
