Overvoltage Phenomena

The electrical insulation withstand levels of individual pieces of equipment, and power-system insulation coordination, are essential engineering subjects. However, before discussing these topics, this chapter examines all types of overvoltage phenomena, including steady-state and temporary overvoltages that occur under nominal or temporary conditions, as well as overvoltages due to lightning or switching. Neutral-grounding methods can be classified as effective neutral grounding (or solidly neutral grounding) and noneffective neutral grounding. The difference between the two practices is the difference in the zero-sequence circuit from the viewpoint of power network theory. Therefore, all power-system behavior characterized by the neutral-grounding method can be explained as phenomena related to the characteristics of the zero-sequence circuit. The chapter explains some typical features of neutral-grounding methods. By using a plain expression for the non-effective grounded system, grounding fault currents can be reduced considerably, but on the other hand, higher temporary overvoltages are caused during faults.