Probabilistic Methods For Counting Equipment Trips Due To Voltage Sags

The exact and precise counting of equipment trips is essential for accurate economic assessment of power quality. This paper discusses the uncertainty involved in the behavior of sensitive equipments used in various industrial processes. It suggests and compares two probabilistic methodologies to incorporate this effect in quantifying the equipment trips due to voltage sags over a specified time period. One method makes use of ordinary probabilities to represent uncertainty involved with the equipment's sensitivity whereas, the other is based upon cumulative probabilities. Existing standards and published test results for the sensitivity of these equipments are critically reviewed. Four different probable behaviors within respective sensitivity ranges are considered for stochastic assessment of equipment trips due to voltage sags. The methodology is illustrated on a generic power system