Using probability concepts to resolve power quality complaints

Power quality problems and customer demands for their resolution are expected to increase as nonlinear loads and sensitive electronic equipment proliferate throughout power systems. Resolving these problems often requires the application of power quality monitors to determine waveform quality and aid in problem diagnosis. Investigators must optimize limited personnel and equipment resources while resolving problems expeditiously. This paper presents a mathematical approach to use as a basis for efficient utilization of resources such as power monitors and personnel. For example, consider the nuisance tripping of an adjustable speed drive at a certain time of day and on certain days of the week. In such an instance, the investigator may attempt to establish the period between occurrences and use this information in pursuing the cause. The determination of how to use this information may be based upon experience without any realization that an application of probability concepts and rules-of-thumb is being used. At any given time the investigator will know the number of complaints needing attention. Based upon the observed periodicity of the occurrences, informed decisions may be made to allocate equipment and personnel to resolve the maximum number of problems in a minimum time. In an attempt to validate this mathematical approach, existing power quality case histories are examined.