ABSTRACT
Electrical insulation is required for preventing short-circuit faults occurring in electrical equipment and systems (e.g., Ragaa, 2012). In addition to normal electrical stress, electrical insulation is often exposed to abnormal electrical stress such as higher-frequency harmonics and impulse voltages produced from a variety of causes, for example, due to switching, lightning voltage impulses and so on. (Ariastina and Blackburn, 2000). Such effects can transiently produce short-duration, unsustainable electrical discharges which are known as partial discharges (PDs). Repetitive exposure to such discharges can eventually lead to undesirable insulation failure. Consequently, monitoring such partial discharges unobtrusively provides a means for tracking any impending failure of the electrical insulation which can have an undesirable impact upon equipment and system operation. Partial discharges can be of different forms. Figure 18.1a shows a PD known as a “tree” formed along the surface of an electrical insulator (Cavallini et al., 2004). Partial discharges may also be formed within solid electrical insulators (Figure 18.1b) or within liquids such as electrically insulating oils (Figure 18.1c) (Ariastina and Blackburn, 2000).
