Development Of Voltage Quality Monitor And Analysis System

Power system voltage on-line monitoring is important for analyzing voltage quality and investigating the cause of power system fault. Although the existing power quality monitoring instruments have excellent performances, they are not convenient to be popularized. A voltage quality monitoring system integrating with the Capacitor Voltage Transformer (CVT) is developed.First, the harmonic analysis method based on FFT is discussed, and some practical issues in the application of FFT are investigated. The factors which affect the calculation precision of harmonics, such as sampling and weighting of window function, are analyzed, and then the instructive conclusions for designing voltage monitor are obtained. To capture the disturbance voltage waveforms, the generating method of start signal for waveform-recording is proposed on the basis of characteristics and classification of typical voltage disturbances, and its feasibility and validity are illustrated by simulation. With the help of MATLAB simulation, the application of wavelet analysis in voltage disturbance detecting is discussed, and the result indicated that the db4 wavelet with six-layer decomposition could detect all the typical disturbances and point out the starting and ending time.On the foundation of theoretical analysis mentioned above, a voltage monitor system is developed. It is composed of a CVT embedded voltage monitor and voltage quality analysis software. The monitor can detect voltage amplitude and voltage harmonics on line, and record waveform of disturbance voltage. The sampled data can be stored in computer by communication and can be reprocessed by the analysis software. In this paper, the design scheme, key circuits, and flow-chart of key software module are described in detail.