Analyzing and maintaining power quality in an electrical power system (EPS) is essential to ensure that power generation, distribution, and loads function as expected within their designated operating regimes. Standards such as MIL-STD-704 and associated documents provide the framework for power quality metrics that need to be satisfied under varying operating conditions. However, analyzing these power quality metrics within a fully integrated EPS based solely on measurements of relevant signals is a different challenge that requires a separate framework containing rules for data acquisition, metric calculations, and applicability of metrics in certain operating conditions/modes.
Many EPS employed throughout industry and government feature various alternating-current (ac) power systems. Ac systems have similar power quality metrics as direct-current (dc) systems, but also feature additional metrics for frequency and phase angle, which are part of the ac signal (unlike dc signals, for which frequency and phase angle have no meaning). Generally, the different signal components cannot be directly measured, hence it is necessary to introduce algorithms that extract amplitude, frequency, and phase angle information, which significantly complicates the overall power quality analysis process. The paper focuses on methods to determine the ac signal components from instantaneous time-domain measurements for three-phase power systems during post-processing. In addition, the methods and mathematical procedures required to determine ac power quality metrics defined in most standards are presented. A representative example is utilized to illustrate the individual metrics and algorithms that have been implemented in a power quality analysis toolbox.