A Single Monitor Method for Voltage Sag Source Location using Hilbert Huang Transform

Abstract: This study introduces a method for voltage sag source location based on Hilbert Huang transformed monitored current signal. Unlike the traditional method, the proposed method first transforms the recorded current during the sag event to obtain frequency-time plot (Hilbert spectra) and IMF plot before the location of voltage sag source is determined. Then based on the change in frequency and IMF the relative location of voltage sag source is obtained. The effectiveness of the proposed method has been verified through simulation on 20 bus system and by comparing with an existing S-Transform based method. The results show that the presented method can determine the location of voltage sag source correctly

Incidencia de los armónicos en la red de distribución eléctrica causada por la inclusión de vehículos eléctricos

Nowadays, the inclusion of electric vehicles in the automotive market has been gradually introduced for reasons such as environmental friendliness, a more efficient engine, among others; and regarding to the increase in the number of automobiles, it is necessary to know the effect they produce on electricity networks, since being nonlinear loads this equipment emits a significant amount of harmonics distortion, which is why this document presents an analysis of the effect of the harmonics in the electrical distribution network as a consequence of the insertion of electric vehicles, for purposes of the study, the analysis was carried out by the mathematical tool called Hilbert-Huang Transform. First, a reconstruction of the electrical signal with the voltage and current data obtained from the electrical vehicle charge which in this case was a Renault Twizy was completed, later a statistical analysis was done to determine the probable density and the probability of occurrence of the events of harmonic distortion, the Empirical Mode Decomposition Method (EMD) was also used, and consists of decomposing any temporal signal into a series of functions that are clearly oscillating called Intrinsic Mode Functions (IMF). Then with this the instantaneous frequency spectrum of the initial series is obtained by applying the Hilbert transform, thus being able to perform the analysis in the time-frequency domain of the harmonics produced by the electric vehicle, it is important to emphasize that the Fourier Transform served as support for this analysis and to compare the benefits that one relationship has to the other.Hoy en día se ha ido dando de manera paulatina la inclusión de vehículos eléctricos en el mercado automovilístico por razones como la amigabilidad con el medio ambiente, un motor más eficiente, entre otras; y en relación a que el número de autos va en aumento es necesario conocer el efecto que estos producen en las redes eléctricas, ya que al ser cargas no lineales estos equipos emiten una importante cantidad de distorsión armónica, es por esto que en este documento se presenta un análisis acerca de la afectación o incidencia de los armónicos en la red de distribución eléctrica a consecuencia de la inserción de vehículos eléctricos, para efectos del estudio, el análisis se lo llevó a cabo mediante la herramienta matemática denominada Transformada de Hilbert-Huang. Lo primero que se hizo fue una reconstrucción de la señal eléctrica con los datos de voltaje y corriente obtenidos de la toma de carga del vehículo eléctrico que en este caso fue un Renault Twizy, luego se realizó un análisis estadístico para determinar la densidad de probabilidad y probabilidad de ocurrencia de los eventos de distorsión armónica, también se usó el Método de Descomposición de Modo Empírico (EMD), el cual consiste en descomponer cualquier señal temporal en una serie de funciones que son netamente oscilatorias llamadas Funciones de Modo Intrínsecas (IMF) luego con esto se obtiene el espectro de frecuencia instantáneo de la serie inicial aplicando la transformada de Hilbert pudiendo con esto realizar el análisis en el dominio tiempo-frecuencia de los armónicos producidos por el vehículo eléctrico, es importante resaltar que la Transformada de Fourier sirvió de apoyo en este análisis y para comparar las bondades que tiene una respecto a la otra

Modified methods for voltage-sag source detection using transient periods

Real-time detection of the voltage sag sources' relative location requires fast and accurate methods. Therefore, in this paper, the transient period of voltage sags is used with useful detection information, which is not considered in the literature. In this context, this work firstly analyses the main positive-sequence phasor-based (PB) and instantaneous-based (IB) methods within both transient and steady-state periods of voltage sags caused by network faults and transformer energizing. Secondly, new methods are proposed using five different modifiers, applied in the transient period of voltage sags, i.e., half and one cycle time windows, to achieve a faster and more accurate response. These modifiers use the PB/IB criteria obtained from the existing methods, such as power, impedance, and current, and are applied as: The mean of the criterion changes, the first largest peak (FLP) on the criterion changes, the mean of the zero-mean criteria during a sag, the FLP of the zero-mean criteria during a sag, and the Trend (slope) of criteria's trajectories versus time. Voltage sag source detection methods are evaluated by applying 1992 simulated voltage sag events in a Brazilian regional power network. The results reveal that the proposed modifiers, used in the new methods, improve the ineffective existing methods by taking half/one cycle within a transient period of voltage sags. The modifiers also show an accuracy equal to other existing enhanced methods due to employing them within the transient period, thus evidencing their appropriateness. Correspondingly, a selection is made amongst the new modified methods in order to choose the most accurate time window (half or one cycle) for the methods. The selected modified methods are also tested by applying field measurements in a Slovenian power network to confirm their effectiveness in the transient short periods. According to a recommendation of the fastest and most accurate new methods in this study, an important application can be using the recommended methods as the directional function in the relays, along with an accurate voltage sag/fault inception time detection algorithm in real-time