Power system disturbance patterns

The author presents some power system disturbance patterns that were obtained by continuously monitoring the power supply of a computer system over a period of two years. An examination of the undervoltage disturbance patterns over this two-year period revealed that the majority of disturbances occurred during normal working hours (8 am-5 pm). The characteristic patterns were different from year to year (i.e., similar shape but significantly different frequencies of occurrence). The number of samples in which no disturbances were recorded decreased as the duration of site monitoring increased. The frequency of undervoltage power supply disturbances was strongly correlated with the seasons, and the mean time between undervoltage power supply disturbances was 39.54 h. Each type of power supply disturbance exhibited unique patterns of occurrence with significantly different mean times between disturbances