ABSTRACT
The examination of overvoltages on the power system includes a study of their magnitudes, shapes, durations, and frequency of occurrence. The voltage stresses on transmission network insulation are found to have a variety of origins. Overvoltages stressing a power system can generally be classified into two main types: external overvoltages and internal overvoltages. The most severe lightning stroke is that which strikes a phase conductor on the transmission line as it produces the highest overvoltage for a given stroke current. Lightning is always a major source of damage to power systems where equipment insulation may break down under the resulting overvoltage and the subsequent high-energy discharge. Temporary overvoltages differ from transient switching overvoltages in that they last for longer durations, typically from a few cycles to a few seconds. The adverse effects of overvoltages on power networks can be reduced in two ways: by using protective devices or by reducing their magnitudes wherever the surge originates.
