Matilde de Apraiz

Rapid Voltage Changes in Power System Networks and Their Effect on Flicker

A rapid voltage change (RVC) is a type of power-quality (PQ) disturbance that has not received sufficient attention in the international PQ standards. Presently, EC 61000-4-30, Ed. 3, defines a precise method for RVC detection and analysis. RVCs can cause or contribute to flicker. However, the existing studies on the subject have not found a correlation between the short-term flicker severity index Pst and the parameters of an RVC event. This paper provides an interpretation of this lack of correlation and shows that instead there is a correlation of RVC events with the instantaneous flicker sensation Pinst. This work is based on the analysis of both simulated waveforms containing RVCs and waveforms recorded in low-voltage and medium-voltage locations.

Review of signal processing techniques for detection of transient disturbances in voltage supply systems

This paper presents a review of some of the most commonly used signal processing techniques for detection and extraction of transient disturbances in voltage supply systems. The performances of different time-domain and frequency-domain methods are compared using different test signals. The advantages and disadvantages of each method are discussed highlighting the potential of each method according to the application.

A laboratory for time-frequency analysis of power quality disturbances using wavelets

This paper presents a laboratory for time-frequency analysis of power quality disturbances using wavelets. Wavelet-packet transform is applied to simulated or real disturbance records previously recorded by power quality monitoring equipment using different mother wavelet function, sampling frequency and different wavelet decomposition trees, computing the magnitude, mean and standard deviation, number of peaks, energy or entropy of the output coefficients at different resolution levels for extraction of the distinctive features of power quality disturbances.

A new method for real-time detection of transient disturbances in low-voltage supply systems

This paper presents a new method for real-time detection and extraction of transient disturbances in low-voltage supply systems. The algorithm developed is based on the sliding window method and applies the discrete wavelet transform to a difference signal obtained comparing each voltage sample with its corresponding sample in the previous period. The algorithm proposed computes the energy of the different output frequency bands of the residual signal corresponding to a one fundamental period, detecting a transient disturbance within the next period of the input signal when a specific threshold is surpassed. The results obtained demonstrate the good performance of the method proposed.

Tracking time-varying waveform distortion in power systems using filter banks

This paper presents a method for tracking time-varying waveform distortion in low voltage supply systems using wavelet filter banks. The method proposed decomposes and reconstructs the input signal in selected frequency bands using a multi-stage wavelet filter bank, to provide a clear visualization of the time-varying nature of waveform distortion for its analysis. The results obtained, both in simulation and using real power signals, show a good performance of the method developed to extract each harmonic component of a signal in the time domain.

A wavelet-based transient detector for P and M class phasor measurement unit integration

In this paper a wavelet-based transient detector is proposed for P and M class phasor measurement unit (PMU) integration. The input waveform in the sampling window is analyzed looking for the local maxima in wavelet coefficients in three different levels to detect a transient previous to the computation of the phasor. If no transients are detected in the wavelet coefficients, the signal is considered stationary, otherwise the signal is considered in dynamic state, so allowing the estimation of the phasor using the most appropriate measurement algorithm for the actual operation conditions. This paper presents some of the preliminary results obtained in the detection of step changes in magnitude and in phase angle and oscillatory and high-frequency transients, also studying the effect of noise and harmonic distortion on the performance of the detection method.

Limitations in the use of the IEC standard method for detection and analysis of rapid voltage changes in power system networks

IEC 61000-4-30 has recently defined a method for detection and analysis of rapid voltage changes in power system networks. This paper presents some of the results obtained in the application of the IEC standard method in different low-voltage and medium-voltage power system networks with different load types and some of the limitations found in the standard method for the correct detection and characterization of these voltage events.

Detection and analysis of transient disturbances in a low-voltage supply system

This paper presents the results of several months monitoring of low-frequency transient disturbances in a low-voltage supply system. A double stage time-frequency domain method is used for real-time detection, capture and analysis of transient disturbances. The paper describes the performance of the instrument used and the analysis of the transients detected as a function of their peak magnitude, duration, frequency components, type of transients, frequency of occurrence and effects on equipment.