In order to assess the effect of sensitive equipment by voltage sag accurately, a voltage sag characteristic identification method is proposed, which based on the consequences of state and process parameter immunity time (PIT). The characteristics of voltage sag is classified to a basic set and an additional set and the concepts of voltage sag characteristic set, virtual voltage sag and influenced event of sensitive equipment caused by voltage sag are introduced in this study. Using PIT to measure the consequences of state of equipment to voltage sag. Using the duration, that from the sag occurs to the process parameter reach to the acceptable limit value, as PIT. The mapping relation between virtual voltage sag characteristic and PIT is studied in this paper, using limit value of acceptable process parameter to identify the sensitive characteristics. Using the tests on PV inverter and personal computer (PC) to verify the proposed method. The result shows that the sensitive sag characteristics of PV inverter includes magnitude, duration and phase-angle jump, the sensitive sag characteristics of PC are magnitude and duration. The identification results proposed by the method are consistent with the test result, proving the correctness and rationality of the proposed method.
