Sag Features Research Articles

Context-aware voltage sag waveform decomposition method using hybrid models for complex power quality detection

To analyze the voltage sag characteristics of distribution networks, automotive companies need an accurate and efficient non-stationary signal analysis tool to extract voltage sag feature information from power quality monitors and fault recorders, which is crucial for automotive companies to analyze grid characteristics and improve localized charging strategies. We innovatively propose a hybrid decomposition method to decompose voltage sag waveforms from composite disturbance data. Subsequently, we design a context-aware mechanism to adapt the proposed decomposition method to the complex power quality data in different regions. In addition, tests were conducted on an integrated power quality simulation system to verify that this method can accurately decompose the voltage sag waveform from the composite disturbance signals. Finally, the experimental simulation results also show the better performance of the method in decomposing voltage sag waveforms with different causes in different composite disturbance signals compared with other mainstream methods.

Detection method of voltage sag disturbance based on improved HHT

In order to improve the detection accuracy of Hilbert Huang transform (HHT) for voltage sag signal, an improved HHT method is proposed: the boundary local feature scale method is combined with CEEMDAN, the former is used to suppress the end effect in the EMD process, and the latter is used to improve the mode aliasing between IMF components. The simulation results show that the improved method can extract the instantaneo us characteristics of the disturbance signal more accurately and quickly, and realize the accurat e positioning of the start and end moments of the sag. Finally, the measured data is used to compare the traditional HHT and the improved HHT method. The results show that the improved HHT method improves the detection accuracy of the sag signal, and has certain reference value for the study of voltage sag feature extraction.

Voltage sag analysis based on cluster analysis and correlation analysis

Based on data mining algorithm, a voltage sag analysis method is proposed, which first performs clustering analysis and then correlation analysis. Firstly, the climatic factors are used to cluster the data, and then the correlation analysis of each cluster is carried out according to the selected voltage sag feature dimensions, finally, the strong association rules are obtained. Through the analysis of the example, it is found that there are some certain correlations between the climatic factors, the voltage sag dimensions and the causes of the voltage sag. These correlations can provide a theoretical basis for the prevention and control of voltage sag.

Origin of the hydrate bound gases in the Juhugeng Sag, Muli Basin, Tibetan Plateau

The Juhugeng Sag, located in northwest of the Muli Basin, Tibetan Plateau, has been investigated for coal and petroleum resources during the past several decades. There have been successful recoveries of gas hydrates during recent years from the Middle Jurassic Yaojie Formation that offer insight into the origin of the hydrocarbon gases from the complex sag feature. This study examines the organic geochemical and stable carbon isotopic characteristics of shale and coal samples from the Middle Jurassic Yaojie Formation of the Juhugeng Sag, as well as compares with carbon isotopes, gas amounts and components of hydrate-bound gas. A total of 19 samples from surface mining, including 12 samples of black shale and 7 samples of coal, were analysed using a micro-photometer, a gas chromatograph, Rock–Eval and isotope methods. All the shale samples contained 100% type I kerogen, and the random vitrinite reflectance values vary from 0.65% to 1.32% and achieve thermal pyrolysis phase. Isotope values of methane (δ13C ranging from − 52.6‰ to − 39.5‰ and δD ranging from − 285‰ to − 227‰) in the hydrate bound gases suggest that the methane originates mainly from thermogenic contributions. It is proposed that ethane from the gas hydrate is thermogenic-produced, and this conjecture is supported by the fact that most of the gas hydrate also contains more than 30% of thermogenic C2+ hydrocarbons and is similar to structure II hydrate. Carbon isotope data from the gas hydrates show a positive carbon isotope series (δ13C1 < δ13C2 < δ13C3), with ethane δ13C values being lighter than − 28.5‰, as high consistency with source rocks from the Jurassic period indicate thermal oil-prone gas. A model of the accumulation of gas hydrate is plotted. However, the gaseous sources of gas hydrates may be a subject for more research.

A novel voltage sag approach during unintentional islanding scenarios: A survey from real recorded events

In this paper, a new voltage sag approach is analytically modelled and validated using both simulation and field measurements. The main aspect of this approach is to propose a new voltage sag feature which appears during unintentional islanding operations (IOs). The unintentional IO occurs when an induction motor is removed from the main utility following a circuit breaker (CB) clearing, transiently, the induction motors (IMs) are acting as generators maintaining the affected distribution feeder with voltage until it is reconnected. The voltage sag modelled in the current article follows an exponential form, as a matter of fact, here it will be demonstrated that the proposed model reaches satisfactorily the field measurements and evidences the dependability of the model adopted. Furthermore, it is worthwhile to note that this novel power quality (PQ) event has not been investigated yet and enhances voltage sag studies. Lastly, it is crucial to point out that all recorded events and a large amount of data needed so as to validate this transient, has been measured in a distribution network (DN) located in Spain.

Discovery of Hesigewula Sag on the western margin of Da Hinggan Mountains in China and its significance in petroleum geology

ABSTRACT With Songliao Basin in northeast China entering the middle-late stage of the exploration and development of oil and gas resources, it is urgent to open up new areas for oil and gas exploration on the periphery of the basin. Five sedimentary sags have been discovered in the western margin of the Da Hinggan Mountains through high-precision gravity, magnetic, and electrical prospecting engineering. According to the conditions of the 5 sags such as buried depth, area, and the scale of source rock, Hesigewula Sag was preferentially selected to deploy two-dimensional seismic prospecting and drilling. As a result, the stratigraphic distribution and structure of Hesigewula Sag were preliminarily ascertained, the main sedimentary facies developed in Aershan Formation-Tengger Formation of the Lower Cretaceous was summarized, and the assessment parameters of source rock of Hesigewula Sag were obtained. According to the research results, the Hesigewula Sag can be divided into 3 second-order tectonic units including the western bulge, the central sag, and the eastern bulge respectively, and the sag was formed mainly subject to the west fractures. Three sedimentary facies including fan delta facies, braided river delta facies, and lacustrine facies have been identified in the Aershan Formation-Tengger Formation of the sag. The source rock in the first member and second member of Tengger Formation in the sag features high abundance of organic matter, meeting the standards of good source rocks. The kerogen of the source rock is mainly of type II1 – II2. The organic matter in the source rock is characterized by low maturity and it entered the evolution stage of low maturity from the second member of Tengger Formation. Furthermore, Hesigewula Sag bears a strong similarity to other petroliferous sags in Erlian Basin in structure, sedimentation, source rock, and other characteristics. Therefore, it can be preliminarily determined that Hesigewula Sag boasts great potential for oil and gas resources.

Semi-analytic galaxies – I. Synthesis of environmental and star-forming regulation mechanisms

We present results from the semi-analytic model of galaxy formation SAG applied on the MultiDark simulation MDPL2. SAG features an updated supernova (SN) feedback scheme and a robust modelling of the environmental effects on satellite galaxies. This incorporates a gradual starvation of the hot gas halo driven by the action of ram pressure stripping (RPS), that can affect the cold gas disc, and tidal stripping (TS), which can act on all baryonic components. Galaxy orbits of orphan satellites are integrated providing adequate positions and velocities for the estimation of RPS and TS. The star formation history and stellar mass assembly of galaxies are sensitive to the redshift dependence implemented in the SN feedback model. We discuss a variant of our model that allows to reconcile the predicted star formation rate density at $z \gtrsim 3$ with the observed one, at the expense of an excess in the faint end of the stellar mass function at $z=2$. The fractions of passive galaxies as a function of stellar mass, halo mass and the halo-centric distances are consistent with observational measurements. The model also reproduces the evolution of the main sequence of star forming central and satellite galaxies. The similarity between them is a result of the gradual starvation of the hot gas halo suffered by satellites, in which RPS plays a dominant role. RPS of the cold gas does not affect the fraction of quenched satellites but it contributes to reach the right atomic hydrogen gas content for more massive satellites ($M_{\star}\gtrsim 10^{10}\,{\rm M}_{\odot}$).

Impact of PAJ with varying POW in voltage sag on rotor over-voltage in DFIG-based wind generator

By the help of the vector analysis, this study studied the impact of voltage sag with different characteristics on the rotor over-voltage of doubly fed induction generator (DFIG) using the stator flux analysis. The influence principle of phase angle jump (PAJ) with varying point on wave (POW) on DFIG is presented. Vector analysis method is used to relate voltage sag features, stator flux, and rotor voltage for symmetrical and unsymmetrical voltage sags. Considering the practical constraints of PAJ, the general variation rules of DFIG rotor over-voltage caused by PAJ with varying POW in voltages sag are validated by simulation.

Voltage Sag Detection Method Based on Wavelet Information

Voltage sag is the major power quality problem and receives wide attention. Although wavelet analysis works well for detecting voltage sag features, the existence of noise can reduce the advantages of wavelet method or even make it ineffective. To solve the problem, the paper uses multi-scale wavelet information by multiplying the results of several scales, and then searches the local maxima from the product to find the transition moment of voltage sag. The proposed method can suppress the noise and improve the accuracy for detecting voltage sag features. Simulation result validates the effectiveness of the proposed method.

Characterization of the porosity distribution in the upper part of the karst Biscayne aquifer using common offset ground penetrating radar, Everglades National Park, Florida

• We use common offset GPR to rapidly characterize porosity in karst limestone. • We demonstrate the ability of GPR to characterize subsurface heterogeneities. • The CRIM petrophysical model is used to build field scale GPR-based porosity models. The karst Biscayne aquifer is characterized by a heterogeneous spatial arrangement of porosity and hydraulic conductivity, making conceptualization difficult. The Biscayne aquifer is the primary source of drinking water for millions of people in south Florida; thus, information concerning the distribution of karst features that concentrate the groundwater flow and affect contaminant transport is critical. The principal purpose of the study was to investigate the ability of two-dimensional ground penetrating radar (GPR) to rapidly characterize porosity variability in the karst Biscayne aquifer in south Florida. An 800-m-long GPR transect of a previously investigated area at the Long Pine Key Nature Trail in Everglades National Park, collected in fast acquisition common offset mode, shows hundreds of diffraction hyperbolae. The distribution of diffraction hyperbolae was used to estimate electromagnetic (EM) wave velocity at each diffraction location and to assess both horizontal and vertical changes in velocity within the transect. A petrophysical model (complex refractive index model or CRIM) was used to estimate total bulk porosity. A set of common midpoint surveys at selected locations distributed along the common-offset transect also were collected for comparison with the common offsets and were used to constrain one-dimensional (1-D) distributions of porosity with depth. Porosity values for the saturated Miami Limestone ranged between 25% and 41% for common offset GPR surveys, and between 23% and 39% for common midpoint GPR surveys. Laboratory measurements of porosity in five whole-core samples from the saturated part of the aquifer in the study area ranged between 7.1% and 41.8%. GPR estimates of porosity were found to be valid only under saturated conditions; other limitations are related to the vertical resolution of the GPR signal and the volume of the material considered by the measurement methodology. Overall, good correspondence between GPR estimates and the direct porosity values from the whole-core samples confirms the ability of GPR common offset surveys to provide rapid characterization of porosity variability in the Biscayne aquifer. The common offset survey method has several advantages: (1) improved time efficiency in comparison to other GPR acquisition modes such as common midpoints; and (2) enhanced lateral continuity of porosity estimates, particularly when compared to porosity measurements on 1-D samples such as rock cores. The results also support the presence of areas of low EM wave velocity or high porosity under saturated conditions, causing velocity pull-down areas and apparent sag features in the reflection record. This study shows that GPR can be a useful tool for improving understanding of the petrophysical properties of highly heterogeneous systems such as karst aquifers, and thus may assist with the development of more accurate groundwater flow models, such as those used for restoration efforts in the Everglades.

Lens surface roughening for tears invariant contact lens performance

In many extended depth of focus diffractive or interferometry based ophthalmic contact lenses the time varied tears layers affect the ophthalmic functionality of the lens. In this paper we present a new approach involving nano pillars realized inside the grooves of a contact lens aiming to implement any type of extended depth of focus or diffractive optical element for ophthalmic applications in order to solve the micro fluidics layer uncertainty within the micro sag features.

Fault Section Location in Distribution Network with DG Based on Voltage Sag Correlation Coefficient

A fault location method based on correlation coefficient was proposed in the paper for the distribution system with distributed generation (DG). At first, by acquiring the Thevenin equivalent parameters of each DG to establish simulation model of the actual distribution network. Then voltage sag feature vectors of each bus would be obtained by simulating short-circuit fault at the location of each bus, respectively. Afterwards, by calculating and analyzing the correlation coefficient between each bus and the actual fault node,, suspicious fault sections can be determined. Finally, the fault section was identified by utilizing the associated node of every suspicious fault section .The method could reduce the fault search range obviously, without a massive requirement of measuring devices, and the required data can be obtained easily. Simulation results of a 10kV distribution network with DG showed that the proposed method was accuracy and effective.

Parallel computing for efficient time‐frequency feature extraction of power quality disturbances

Fast signal processing implementation techniques for detection and classification of power quality (PQ) disturbances are the need of the hour. Hence in this work, a parallel computing approach has been proposed to speed up the feature extraction of PQ signals to facilitate rapid building of classifier models. Considering that the Fourier, the one-dimensional discrete wavelet, the time-time and the Stockwell transforms have been used extensively to extract pertinent time-frequency features from non-stationary and multi-frequency PQ signals, acceleration approaches using data and task parallelism have been employed for parallel implementation of the above time-frequency transforms. In the first approach, data parallelism was applied to the Stockwell transform and the time-time transform-based feature extraction methods separately to alleviate capability problems. Also, data parallelism was applied to Fourier and wavelet-based feature extraction methods independently to alleviate capacity problems. Secondly, a combination of task and data parallelism was applied to speed up S-transform based three-phase sag feature extraction. Experiments were conducted using shared-memory and distributed memory architectures to try out the effectiveness of the proposed parallel approaches. The performances of these parallel implementations were analysed in terms of computational speed and efficiency in comparison with the sequential approach.

Quantifying the origin and geometry of circular sag structures in northern Fort Worth Basin, Texas: Paleocave collapse, pull-apart fault systems, or hydrothermal alteration?

Three-dimensional seismic data reveal numerous subcircular sag structures in the northern Fort Worth Basin. The structures are defined by concentric faults that extend vertically upward 760–1060 m (2500–3500 ft) from the Lower Ordovician Ellenburger Group. The largest structures remained active into the lower Desmoinesian Strawn Group. Criteria are outlined for defining seismically resolvable sag structures, and a detailed quantitative analysis of the geometries of these circular features was undertaken. Results are compared and contrasted, with reviews of subsurface collapse mechanisms and strike-slip processes that are known to produce subsurface circular to subcircular sag geometries in plan view. In this manner, we develop several constraints for differentiating collapse-related sag structures from strike-slip–related sag structures. Qualitative analyses indicate that the geometries observed are strongly analogous to subsurface collapse features where material is removed at depth to create a void, into which the overburden subsequently sags and collapses. Quantitative analyses support the formation of these features by incremental collapse and suprastratal deformation above a linked system of coalesced, collapsed paleocaves within the Ellenburger Group. Observations and criteria presented herein provide valuable information in defining seismically resolvable collapse features worldwide and help distinguish sag features of collapse affinity from those of other origins.

A Right-Lateral Structural Model for Poui Field, Offshore Trinidad, from 3-D Seismic Interpretation and Subsurface Well Control

A new wrench fault structural model is developed for Poui Field, in the Colombus Basin, offshore Trinidad. A strain ellipse for a right-lateral simple shear stress field is demonstrated from observed fault patterns on recent seismic mapping of deep hydrocarbon-bearing sands at Poui Field. The seismic interpretation is calibrated by 20 points of well control which penetrated the best, continuous, mappable reflector at these deep sand levels. Seismic cross-sections taken over the Poui structure, which are perpendicular to the structural axis of the feature, and constrained by well control, demonstrate geometries typical of wrench faulting observed along the Los Bajos fault complex, onshore Trinidad, and along the San Andreas wrench fault systems of southern California. Variable dip rate along the fault, flower structures with associated sag features, asymmetry of the structure, an extensional duplex, and a possible horsetail splay appear on the maps and cross-sections, and support the wrench fault model. Various pieces of subsurface information, observed in the Field from well control, support the wrench hypothesis: isolated, pressure separated compartments, abrupt facies changes across faults and hydrocarbon migration anomalies. Subsequent extensional faulting created an overprinting of rotated, normal faulting that followed fracture planes created by the right-lateral simple shear more » stress field. Regional mapping indicates that this wrench fault is a stress field. Regional mapping indicates that this wrench fault is a continuation of the right-lateral fault system mapped onshore Trinidad as the Marcel Main fault system. « less

Pole-ward drift of North America

Thirty-one lines of evidence — structural, seismic, paleomagnetic, and others — are listed to show that North America has been migrating toward the Arctic Ocean area, since the end of Paleozoic time, at about two cm/yr. The North American plate has been pulling away from South America, during that time interval, at about one cm/yr; the Gulf of Mexico is the major tensional feature which has developed in Middle America as a result of that separation. Any eastward or westward drift that has been involved must have been either negligible or of such a nature that both Americas had essentially the same rate of displacement. The northern continent has been reshaped by its migration, becoming narrower (east-west) and longer (north-south). This reshaping has been accompanied by second-order grabens and other sag features in the eastern and western parts.