Study On Voltage Sag And Its Measurement Method

With the development of industry technology,power quality problemshave been displayed gradually and the people have attached importance to them more and more. Voltage sag ,as one of the important aspect of power quality,its research is just underway in our country,which has no criterion related. The purpose of this paper is to offer some reference to the national criterion to be drafted.In the first,the paper study the short duration variations of RMS and discuss the voltage sag emphatically.This thesis put up a new definition of voltage sag,which confirm the duration precisely.In the second, the paper researchs the reason that cause voltage sag emphatically, especially moter starting,and carries on a simulational calculation according to the moter mode,presenting a simulation curve.The paper point out the solution methods of voltage sag due to moter starting.Then, this thesis concerns with the wavelet transform and its application in power system and compare the deficiency vs strongpoint between the Fourier transform ,short-time Fourier transform.This article point out that wavelet transform fit for non-stationary signals analysis and put it into the measurement of voltage sag.Based on the comparion of several algorithm of voltage sag measurement in the literature,the thesis put up a new voltage sag measurement algorithm ---combination of wavlet transform and root-mean-square.The thesis validate the algorithm according to simulation and actual measuring data.