The traditional voltage sag tolerance characteristic curve is usually described as a rectangle.While

it is shown by the test that the voltage sag tolerance characteristic curve of some sensitive devices appear non-rectangle.Therefore

in this paper a kind of a method to describe the non-rectangular uncertain region of voltage sag tolerance characteristic of sensitive equipment is proposed.The non-rectangle description mode of the uncertain region of voltage sag tolerance characteristic curve truly reflecting the voltage sag tolerance characteristics of sensitive equipment is set up.On this basis

the non-rectangle uncertain region of voltage sag tolerance characteristics of sensitive equipment is divided and quantitatively described and a fault probability assessment method of sensitive equipment based on energy loss principle is proposed

which can accurately reflect the impact of voltage sag events on sensitive equipment in actual power grid and avoid over-estimation.The correctness of the proposed method is verified by analyzing and evaluating the voltage sag event in the actual power grid.