Eduardo Gómez-Luna

Current Status and Future Trends in Frequency-Response Analysis With a Transformer in Service

This paper presents the current status and future trends in the application of the frequency-response analysis (FRA) technique with the transformer in service (online) through bibliographic review and analysis. As a result, three basic stages of the online FRA test have been identified and defined: injection and excitation signal measurement; recording, filtering and processing of measured signals; and curve analysis and interpretation. This work presents an overview of the online FRA technique, useful for subsequent research in this area.

Non-intrusive load monitoring based on switching voltage transients and wavelet transforms

Continuous Wavelet Transform (CWT) analysis to find feature vectors for switching voltage transients for Non-Intrusive Load Monitoring (NILM) is presented and discussed, and compared with the previously used short time Fourier transform (STFT). The feature vectors computed from both CWT and STFT were used to train Support Vector Machines (SVMs) that identify the connection or disconnection of appliances for a NILM system. Experimental results show that the CWT analysis based on the complex Morlet wavelet improves classification accuracy as compared to the analysis based on STFT. More importantly, a 20× reduction of the vector size requirement is shown, thus greatly lowering computational requirements. It can be expected that commercial transient-based NILM will be based upon the CWT methods shown here.

Obtaining the Electrical Impedance Using Wavelet Transform From the Time Response

This letter presents a new mathematical concept for electrical impedance based on the transient response, by means of the coefficients energy of the continuous wavelet transform. To validate the new proposed method, signals were simulated in the Alternative Transients Program, and the experimental results were compared with the short time Fourier transform. This contribution has been particularly applied to power transformers in order to identify possible damages from just analyzing the transient responses in the wavelet domain.

Application of Wavelet Transform to Obtain the Frequency Response of a Transformer From Transient Signals—Part 1: Theoretical Analysis

This paper introduces a new theoretical method to obtain the frequency-response curve with the transformer in service (online) from the transient signals analysis by applying the continuous wavelet transform. To validate the method, the transient signals were simulated in the Alternative Transient Program for two cases: 1) under injection of pulses over the 60-Hz wave and 2) under switching operations, respectively. To simulate the transformer, a suitable wide-bandwidth model was employed. This study proposes a new setup of the Morlet wavelet, denominated Morlet-Modified, which showed the best results obtained for our application purpose (FRA On-line). This paper is a contribution for signal processing for the online frequency-response analysis technique on transformers.

Application of Wavelet Transform to Obtain the Frequency Response of a Transformer From Transient Signals—Part II: Practical Assessment and Validation

This paper presents a practical assessment and validation for the new proposed approach based on the continuous wavelet transform (CWT) to obtain the frequency response from online transient signals for an actual transformer. Apart from the mathematical procedure, an electronic system was also designed and implemented in order to inject superimposed controlled pulses to the power system (50/60 Hz) wave. The results show improved performance of the wavelet transform compared to the Fourier transform, for transient signal analysis to be applied on a nonintrusive transformer monitoring approach. Particularly, this new approach enables overcoming some problems related to the signal filtering and the signal processing in an online frequency-response analysis transformer diagnosis. This paper is presented in three parts. Part I showed the main theoretical basis of this approach. The current Part II shows a practical assessment based on tests performed in a three-phase transformer of 1150/345 V-5 kVA and in a single-phase transformer of 13200/240 V-15 kVA. Part III shows the performance of this new approach on transformers being diagnosed under real conditions.

Selección de una wavelet madre para el análisis frecuencial de señales eléctricas transitorias usando WPD

This paper proposes a method to select an appropriate mother wavelet for the frequency analysis of electrical transient signals, based on the wavelet properties and considering the needs of the application case. The Wavelet Packet Decomposition (WPD) was used to analyze wavelets as filters and to quantify the information leakage by evaluating the performance of different families included in the Matlab’s libraries. To validate the method proposed, an application case is presented where the effective value (RMS) is estimated for a transient signal. The selection method used provides a clear scope on how to exploit the wavelet properties to select the appropriate one depending on the particular application.