Study Of Voltage Sag On Typical Sensitive Equipment And Its Propagation Property

This paper mainly focuses on the study of voltage sag on typical sensitive equipment and its propagation property. First of all, mechanism analysis of voltage sag on typical sensitive equipment is reviewed. And on the basis of the review, detailed mechanism analysis of the voltage sag on switch-mode power supply (SMPS) and AC contactor is conducted. With the energy conservation relations of SMPS DC capacitor, the mechanism of voltage sag on SMPS is revealed. Then the mechanism analysis of different voltage sag characteristic index on SMPS is carried out with DC capacitor voltage waveform in PSCAD/EMTDC. Finally, a brief study of the influence of voltage sag on AC contactor is done by analyzing the relationship between the spring force and the electromagnetic force.Based on the mechanism analysis, the test of the sag influence on typical sensitive equipment is taken in this paper. First of all, a program is established for test. Then according to the program, the influence of sag characteristics including voltage sag magnitude, duration, phase-angle jump and point-on-wave of sag initiation on SMPS and AC contactor are tested. After the test, the distribution regularity of sensitive curves is formed through analyzing the test data on record, which verifies the correctness of mechanism analysis as well. Besides, the sensitive curves of and AC contactor under different characteristics are extracted. And the similarities and differences between the sensitivity curves from different brands are analyzed. Special attention is paid on influence of advanced voltage sag characteristics on SMPS and AC contactor. Finally, the test results of various SMPS and AC contactors are integrated. By conducting the extreme processing and adopting the plane fitting principle, sensitivity models of SMPS and AC contactor are developed, which can be used in the analysis of their sensitivity to voltage sag.On the purpose of analyzing the influence of voltage sag on sensitive equipment subjected to low voltage level, a more generalized voltage sag classification method with the consideration of phase shift is proposed on the basis of original methods, and the transformers’effects on phase shift with various voltage sag types are studied as well. Finally, in order to make sag calculation of load and associated nodes easier, the superposed and equivalent calculation methods are proposed. The superposed calculation method is concerned with transforms and lines, and the equivalent calculation is concerned with multiple transforms and load connections. Both of the two methods can improve the accuracy of the sag propagation property theory.