Research On The Location Of Voltage Sag Source

With the marketization of electric power, the power quality problems haveincreasingly caused the electric companies and consumers’ attention. In a variety ofpower quality disturbances, the voltage sag is the most serious power quality problemwith the highest incidence. Therefore, it’s significant for the analysis of disturbancecause and the hazard assessment of disturbance to monitor the voltage sag accurately.However, only a simple test to the voltage sag characteristic can not determinewhether the disturbance source result from the system failure or abnormal operatingconditions occurring in the electric equipment or the disturbance load. Locatingvoltage sag sources can not only helps to locate power system fault, to enhance thefailure-prone equipment monitoring and to achieve status maintenance, but also helpsto further clarify the responsibility and rights of the electric power and the customers,to institute suitable treatment measures and to share the treatment found among themajor responsibility party. Moreover, the study of voltage sag source locationprovides the necessary supervision measures of power quality for the electricregulators, and provides a basis for defining the measure responsibility and mediatingdisputes under the electricity market environment.As yet, study on the voltage sag is concentrated on detection, mechanismanalysis and restraining solutions. But there is less study on the voltage sag sourcelocation. At present, the theoretical studies on voltage sag source location are basedon the characteristics analysis of energy, current and impedance. It is found that theprinciple of these methods is simple and can be mastered easily. However, because ofthe strong assumptions made for the grid model, the existing voltage sag sourcelocation methods have not been able to satisfy actual application.This paper describes the methods applied in identification of voltage sagcharacter, including the half-wave integration, the instantaneous voltage Park’transformation, the Short time Fourier transform and the Wavelet packet transformbased on the square demodulation method. By comparing the tracking performance ofthese methods, this paper analyzes the adaptability of different method in differentsituation. Besides, after the characteristic values of voltage sag are received, this paperdeduces the explicit procedure of assessment when the power system suffers from voltage sag, which is of great significance to evaluate the impact of voltage sags onthe system.A method based on the impedance measurement in dq0coordinate system isproposed in this paper. Firstly, the three-phase voltage and current measured at themonitoring point are transformed by the orthogonal Park’s transformation. And thenthe certain character of obtained three-phase instantaneous impedance measurement isused to locate the sources of the voltage sags. In addition, this paper theoreticallyanalyzes the induction-motor influence to the method of locating voltage sag source.Constant impedance load and induction-motor load are used in digital simulationrespectively. The simulation results show that the method can locate the disturbancesource whether symmetrical or asymmetrical happens.