Estimation of single-event voltage sags using a novel classification method

Estimation of voltage sags has become increasingly crucial with higher penetration of sensitive devices in the system recently. Single-event indices for voltage sags are essential to form the whole system of estimation. However, it is still difficult to tell how serious a sag is even after the assessment value is got, for there's no reference value to compare with. This paper firstly discussed indices of single-event sags. Then the voltage sag energy was recommended as a typical index irrelevant to the sensitive curves. In order to more intuitively describe the severity degree, a novel classification of severity level was proposed by using the reference values. In detail, CP95, CP75, CP50, and CP25 of the index of numerous sag events were determined as the reference values. To make up for the shortage of the Evs, the events come from not only measured data in grids but also the standard sensitive curves. To determine more reasonable and generalized reference values, the analytic hierarchy process (AHP) was applied to synthesize the reference values by giving each value a weight according to their different significance. Numerical examples show the conciseness and the clarity of the classification method which can provide a more intuitive view of the severity of a single-event sag for customers, device manufactures and the utility.