The power system can experience fluctuations in voltage due to factors like single-phase grounding, long-line capacitance effect, and load shedding. These fluctuations can result in either a rise in power frequency voltage or the generation of high-amplitude transient overvoltage. To counter this, lightning arresters are designed to withstand a certain level of power frequency voltage rise for a specific duration of time. Essentially, they provide protection against voltage fluctuations in the power system caused by these factors.