Secondary Extinction Research Articles

Study on a field data of secondary arc extinction time for large-sized transmission lines

Secondary arc extinction time is an important factor, which influences system stability because it directly affects the reclosing time. However, few reports exist on a field data of the secondary arc extinction time on transmission lines. This paper describes the investigation results of secondary arc extinction characteristics by analyzing voltage wave shapes during the lightning faults on 550 kV transmission lines. Recovery voltages and secondary arc currents on each transmission line during faults were calculated to consider correlation with the secondary arc extinction time. The secondary arc extinction time is estimated by the existing formula, the secondary arc current and the recovery voltage required for one second reclosing are evaluated.

A Noncommunication Adaptive Single-Pole Autoreclosure Scheme Based on the ACUSUM Algorithm

In this paper, a new noncommunication-based adaptive single-pole autoreclosure (ASPAR) scheme is proposed, by which the extinction of secondary arc can be detected rapidly, in 4 ms. The proposed algorithm applies the adaptive cumulative sum method (ACUSUM) to a local bus voltage signal in order to reveal the occurrence of three successive events during a fault, that is, fault inception, circuit breaker (CB) opening (primary arc extinction), and secondary arc extinction; while detection of the last event can lead to CB reclosing. According to the fact that the two first events result in abrupt decreases in local voltage amplitude and the third one imposes an abrupt increase, this sequence of changes in voltage amplitude distinguishes temporary faults. To evaluate the robustness of the proposed scheme against transient faults, the results of investigations on different conditions, including fault location, amount of load, power-flow direction, and short-circuit levels of local and remote buses are presented; where, in all cases, the highest reliability has been achieved.

Nullifying the extinction effect in XRD characterization of fibre textures

To gain accuracy and, hence, physical reality of the data acquired by XRD measurements of fibre textures, a technique is elaborated to achieve experimental values, which are free of extinction effects. Its elaboration is based on combining basic definitions of the extinction theory and texture analysis. This technique is applicable to characterization of metal coatings that appear infinitely thick for X-rays. A nickel sample representing <100> + <221> texture components is used as a model. Resultant derived series of data on pole-density distribution of the {200} diffraction pole figure shows that the data corresponding to the main <100> texture component are strongly affected by extinction. On the contrary, due to definitions that require reduction of the intensity distribution to multiples of random density, the extinction-free values of the volume fraction of texture components do not differ substantially from those calculated by standard methods. Evidently, any of the standard methods for volume fraction measurements provides reasonable data if secondary extinction is even disregarded.

The form of direct interspecific competition modifies secondary extinction patterns in multi‐trophic food webs

Forcibly removing species from ecosystems has important consequences for the remaining assemblage, leading to changes in community structure, ecosystem functioning and secondary (cascading) extinctions. One key question that has arisen from single‐ and multi‐trophic ecosystem models is whether the secondary extinctions that occur within competitive communities (guilds) are also important in multi‐trophic ecosystems? The loss of consumer–resource links obviously causes secondary extinction of specialist consumers (topological extinctions), but the importance of secondary extinctions in multi‐trophic food webs driven by direct competitive exclusion remains unknown. Here I disentangle the effects of extinctions driven by basal competitive exclusion from those caused by trophic interactions in a multi‐trophic ecosystem (basal producers, intermediate and top consumers). I compared food webs where basal species either show diffuse (all species compete with each other identically: no within guild extinctions following primary extinction) or asymmetric competition (unequal interspecific competition: within guild extinctions are possible). Basal competitive exclusion drives extra extinction cascades across all trophic levels, with the effect amplified in larger ecosystems, though varying connectance has little impact on results. Secondary extinction patterns based on the relative abundance of the species lost in the primary extinction differ qualitatively between diffuse and asymmetric competition. Removing asymmetric basal species with low (high) abundance triggers fewer (more) secondary extinctions throughout the whole food web than removing diffuse basal species. Rare asymmetric competitors experience less pressure from consumers compared to rare diffuse competitors. Simulations revealed that diffuse basal species are never involved in extinction cascades, regardless of the trophic level of a primary extinction, while asymmetric competitors were. This work highlights important qualitative differences in extinction patterns that arise when different assumptions are made about the form of direct competition in multi‐trophic food webs.

Research on a novel suppressing methodology for secondary arc extinction based on an impedance paralleled to line circuit breaker

A novel scheme is proposed for secondary arc extinction, preferably applicable to extra high voltage (EHV) and ultra high voltage (UHV) transmission lines. The topology and the operational principle of the scheme are elucidated in details. Mathematical expressions for topology parameters design and optimization under different conditions have been established based on equivalent circuit transform and are verified by simulations. Results suggest that the proposed methodology can largely reduce the forced component of the secondary arc current, one part of the complete response of a circuit under excitation. The recovery voltage is not affected by fault location, transmission power and the shunt inductors. The decay factor and oscillation frequency of the free components of the secondary arc current and the recovery voltage are also computed based on the equivalent impedance network and Laplace Transform. In addition to causing possible resonant overvoltage, the proposed theme may prolong the arcing time due to cancelling zero-crossing of the secondary arc current while shunt inductors are installed at the transmission line terminals. Simplified formula for calculating the critical compensation point are given as to be used as a reference for the re-optimization of the novel theme. The proposed methodology presents an alternative to suppress the secondary arcs for EHV and UHV transmission lines. Copyright © 2013 John Wiley & Sons, Ltd.

Late Cretaceous restructuring of terrestrial communities facilitated the end-Cretaceous mass extinction in North America

The sudden environmental catastrophe in the wake of the end-Cretaceous asteroid impact had drastic effects that rippled through animal communities. To explore how these effects may have been exacerbated by prior ecological changes, we used a food-web model to simulate the effects of primary productivity disruptions, such as those predicted to result from an asteroid impact, on ten Campanian and seven Maastrichtian terrestrial localities in North America. Our analysis documents that a shift in trophic structure between Campanian and Maastrichtian communities in North America led Maastrichtian communities to experience more secondary extinction at lower levels of primary production shutdown and possess a lower collapse threshold than Campanian communities. Of particular note is the fact that changes in dinosaur richness had a negative impact on the robustness of Maastrichtian ecosystems against environmental perturbations. Therefore, earlier ecological restructuring may have exacerbated the impact and severity of the end-Cretaceous extinction, at least in North America.

The Research of Secondary Arc Spectrum Characteristics on UHV

On UHV power transmission lines, when single-phase ground fault happen, it will appear secondary arc on lines, the existence of secondary arc impact on the stable operation of system. The effectiveness of single-pole autoreclosure (SPAR) in maintaining power system stability is largely determined by the speed with which secondary arc extinction, and hence autoreclosure, can be achieved. The paper adopts total harmonic distortion (THD) to judge the status of arc. First, the simulation model of secondary arc is established by ATP software. Then, faulted phase voltage and secondary arc are simulated in different close angle. Last, spectrum characteristics and harmonic content of faulted phase voltage and current are analyzed in different close angle, at the same time, THD of non-faulted phase is also analyzed by Fourier algorithm. Through the fault phase voltage and current simulation and Fourier analysis, which comes to the conclusion that at the peak in the power supply voltage secondary arc is the most difficult to extinguish and the harm to insulation is the greatest. DOI: http://dx.doi.org/10.11591/telkomnika.v10i6.1411 Full Text: PDF

Can cool flames support quasi-steady alkane droplet burning?

Experimental observations of anomalous combustion of n-heptane droplets burning in microgravity are reported. Following ignition, a relatively large n-heptane droplet first undergoes radiative extinction, that is, the visible flame ceases to exist because of radiant energy loss. But the droplet continues to experience vigorous vaporization for an extended period according to a quasi-steady droplet-burning law, ending in a secondary extinction at a finite droplet diameter, after which a vapor cloud rapidly appears surrounding the droplet. We hypothesize that the second-stage vaporization is sustained by low-temperature, soot-free, “cool-flame” chemical heat release. Measured droplet burning rates and extinction diameters are used to extract an effective heat release, overall activation energy, and pre-exponential factor for this low-temperature chemistry, and the values of the resulting parameters are found to be closer to those of “cool-flame” overall reaction-rate parameters, found in the literature, than to corresponding hot-flame parameters.

EMTP-RV를 이용한 2차 아크 모델링

Most of faults occurred in transmission lines are single-phase to ground faults and transient faults. Single-phase auto reclosing is an appropriate scheme to maintain the system stability and restore the system effectively when those faults are occurred. In single-phase auto reclosing scheme, the secondary arc is generated after faulted phase is tripped to eliminate the fault and it is sustained by the capacitive and inductive coupling to the healthy phases. It is important to reclose the faulted phase after fully extinction of secondary arc because of the damage applied to system. Therefore, it is necessary to research on the detection of secondary arc extinction to ensure high success rate of reclosing. In this step, firstly, the accurate modelling of secondary arc should be performed. In this paper, the modelling of secondary arc is performed by using EMTP-RV and the simulation results show that the implemented model is correct and effective.

Adaptive foraging and the rewiring of size-structured food webs following extinctions

Over the past decade, attempts have been made to characterise the factors affecting the robustness of food webs. Many studies have been carried out using a “topological” approach, in which secondary extinctions in ecological networks are determined by the structure of the network alone. These studies have led to numerous insights; for example how robustness is highly dependent on the order of extinctions, the fraction of basal species, as well as the connectance of the webs. But there has been criticism of these investigations for their lack of biological realism, such as the inability of species to alter their diets when species are lost, or the reliance on the criterion that a species only suffers a secondary extinction once it loses all its resources. Here, building on past approaches, we address these issues by introducing allometric optimal foraging theory to explore the consequences of species adaptively responding (by altering feeding links) to loss of prey in size-structured food webs. We also explore the effect on robustness of a secondary extinction criterion based on a threshold of energy loss, rather than merely the absence of a connection to at least one prey. We show that both rewiring and energetic extinction criteria greatly affect the robustness of model food webs, and that these new factors interact with each other as well as with the body mass distribution of the community, to shape the complexity–robustness relationship.

Secondary extinction in Pavlovian fear conditioning

Pavlov (1927/1960) reported that following the conditioning of several stimuli, extinction of one conditioned stimulus (CS) attenuated responding to others that had not undergone direct extinction. However, this secondary extinction effect has not been widely replicated in the contemporary literature. In three conditioned suppression experiments with rats, we further explored the phenomenon. In Experiment 1, we asked whether secondary extinction is more likely to occur with target CSs that have themselves undergone some prior extinction. A robust secondary extinction effect was obtained with a nonextinguished target CS. Experiment 2 showed that extinction of one CS was sufficient to reduce renewal of a second CS when it was tested in a neutral (nonextinction) context. In Experiment 3, secondary extinction was observed in groups that initially received intermixed conditioning trials with the target and nontarget CSs, but not in groups that received conditioning of the two CSs in separate sessions. The results are consistent with the hypothesis that CSs must be associated with a common temporal context during conditioning for secondary extinction to occur.

Visual evaluation of the length of artificially generated electrical discharges by 3D-snakes

The secondary arc extinction is the main concern in single-phase auto reclosure (SPAR) switching studies, since it dictates whether the reclosure will be successful or not. In this context, a function that describes the arc length variation over time (l(t)) is an important information not only for dynamic response but also for the analysis of transient arc processes. Given that purely electrotechnical approach only gives a profile of the curve l(t), the application of techniques based on image analysis has been considered for obtaining such function. In this paper, a new approach based on 3D-reconstruction and the tracking of an electrical arc is proposed for performing a computer-based evaluation of variations in its length. It was applied a three-dimensional active contour named 3D-snake that is geometrically represented by a B-spline, which evolves in 3D space. This new model is much less dependent on the determination of homologous points than the ad hoc approaches found in the literature for recovering 3D geometry of electrical discharges based on image analysis. In addition, the proposal presented is capable of tracking the evolution of the electrical discharge taking into account the time dependence between consecutive pairs of frames in two videos providing the required function l(t).

Design of a novel phasor measurement unit-based transmission line auto reclosing scheme

This study presents an adaptive transmission line auto-reclosing scheme based on synchronised phasor measurement units. This scheme uses voltage and current phasors of different sequences at both ends of a transmission line to effectively classify transient and permanent faults occurring on transmission lines. In the case of a transient fault this scheme can provide a variable and adaptive dead time for reclosing circuit breakers via the detection of secondary arc extinction. System simulation studies show that the proposed scheme achieves excellent performance in classifying transient and permanent single-phase faults and estimating the secondary arc extinction time for correct auto-reclosing.

Adaptive Single-pole Auto-reclosure for Transmission Lines Using Sound Phases Currents and Wavelet Packet Transform

This article presents a novel approach for adaptive single-pole auto-reclosing of power transmission lines under transient single-phase fault conditions by using a wavelet packet transform. In the proposed method, the mode current (sum of the currents of the two healthy phases) is captured with a sampling rate of 10 kHz and de-noised using the db8 wavelet packet to obtain signals with higher signal-to-noise ratio. The db8 wavelet packet is then used to decompose the mode current signal to attain the coefficients of wavelet nodes 131, 133, 134, 136, 137, 139, and 140 and to define an index, which is the sum of the absolute values of these node coefficients. The index is used to distinguish transient (arcing) faults from permanent faults and also to identify the secondary arc extinction instant. The proposed method has been successfully tested under a variety of fault conditions on a 500-kV overhead line using electromagnetic transient program. The test results validate the algorithm ability in distinguishing between transient and permanent faults and determining the instant of secondary arc extinction. The significant advantage of the proposed algorithm is that it does not need a case-based threshold level, and therefore, its performance is independent of fault location, line parameters, and pre-fault line loading conditions. Moreover, the algorithm can be used in transmission lines with reactor compensation.

A wavelet packet based method for adaptive single-pole auto-reclosing

We present a new algorithm for adaptive single-pole auto-reclosing of power transmission lines using wavelet packet transform. The db8 wavelet packet decomposes the faulted phase voltage waveform to obtain the coefficients of the nodes 257, 259 to 262. An index is then defined from the sum of the energy coefficients of these nodes. By evaluating the index, transient and permanent faults, as well as the secondary arc extinction instant, can be identified. The significant advantage of the proposed algorithm is that it does not need a threshold level and therefore its performance is independent of fault location, line parameters, and operating conditions. Moreover, it can be used in transmission lines with reactor compensation. The proposed method has been successfully tested under a variety of fault conditions on a 400 kV overhead line of the Iranian National Grid using the Electro-Magnetic Transient Program (EMTP). The test results validated the algorithm’s ability in distinguishing between transient arcing and permanent faults and determining the instant of secondary arc extinction.

An Adaline based arcing fault detection algorithm for single-pole autoreclosers

In this paper, a new Adaline based adaptive single-pole autorecloser algorithm is proposed to discriminate permanent and transient faults in HV transmission lines. The proposed algorithm is implemented by processing only terminal voltages and also used to estimate secondary arc extinction time. The algorithm is simulationally analyzed using ATP version of EMTP by varying fault locations and pre fault loading conditions to demonstrate the capabilities and limitations of the method. In addition to that, measured data, which are taken from an actual power system, are also used for testing the algorithm. Results show that the method can successfully be implemented for real time application and computationally less expensive when compared with other methods.

The influence of different Student'sTmosaic distributions on the extinction factor in mosaic crystals

During the preparation of versatile tables for the secondary extinction factor Y(μ) of cylindrical and spherical mosaic crystals expressed as functions of the Bragg angle θ, absorption coefficient times radius μρ and reduced radius τ(0) = σ(0)ρ [σ(0) = (2π)(1/2)Q/η], or of θ, τ(0) and ξ(0) = μ/σ(0), five kinds of Student's Tn probability functions T1, T2, T3, T4, T∞ for describing the mosaic distribution of crystals have been tested. T1 is Lorentzian (L) and T∞ is close to Gaussian (G). The influence of these different mosaic distributions upon the reflection power ratio, the integrated reflection power ratio (the area under the rocking curve) and the extinction factor Y(μ) in cylindrical crystals has been thoroughly investigated. For a weakly absorbing cylindrical crystal with τ(0) = 30, the value of Y(μ) for the T2 distribution turns out to be nearly two times the value for G, but the difference between these distributions becomes small when ξ(0) > 1. The L distribution has been found to be unsuitable for describing the mosaic distribution. The determination of different types of mosaic distribution from the rocking curves is discussed based on these results. Finally T2, T4 and the G distribution have been found to be acceptable for the calculation of secondary extinction factor tables for cylindrical and spherical crystals.

Adaptive single pole auto-reclosing using discrete wavelet transform

This paper proposes a new algorithm for adaptive single pole auto-reclosing (SPAR) using discrete wavelet transform (DWT). The faulted phase voltage signal is captured at a sampling rate of 2.5 kHz. The sym8 wavelet function is used to decompose the signal into level 1 and to define an index function (INDF), which is obtained from the sum of absolute values of detail coefficients of the captured signal at the level 1 resolution. Finally, a decision function (DEF) is defined by computing the second derivative of the INDF. By evaluating the sign of the DEF, transient (arcing) faults are distinguished from permanent faults and also the secondary arc extinction instant can be identified. The significant advantage of the proposed algorithm is that it does not require any threshold level and therefore its performance is independent of fault location, line parameters and operating conditions. Furthermore, it can be used in transmission lines with reactor compensation. The proposed method has been successfully tested under a variety of fault location and load angle on a 400 kV overhead line, with and without reactor compensation, using the Electro-Magnetic Transient Program. The test results validate the algorithm ability in distinguishing between arcing and permanent faults and determining the instant of secondary arc extinction. Copyright © 2010 John Wiley & Sons, Ltd.

The robustness of pollination networks to the loss of species and interactions: a quantitative approach incorporating pollinator behaviour

Species extinctions pose serious threats to the functioning of ecological communities worldwide. We used two qualitative and quantitative pollination networks to simulate extinction patterns following three removal scenarios: random removal and systematic removal of the strongest and weakest interactors. We accounted for pollinator behaviour by including potential links into temporal snapshots (12 consecutive 2-week networks) to reflect mutualists' ability to 'switch' interaction partners (re-wiring). Qualitative data suggested a linear or slower than linear secondary extinction while quantitative data showed sigmoidal decline of plant interaction strength upon removal of the strongest interactor. Temporal snapshots indicated greater stability of re-wired networks over static systems. Tolerance of generalized networks to species extinctions was high in the random removal scenario, with an increase in network stability if species formed new interactions. Anthropogenic disturbance, however, that promote the extinction of the strongest interactors might induce a sudden collapse of pollination networks.

Exploitation, secondary extinction and the altered trophic structure of Jamaican coral reefs

AbstractCoral reef communities of the Greater Antilles in the Caribbean have a long history of anthropogenic disturbance, driven by the exploitation for food of both vertebrate and invertebrate species. Exploitation, coupled with region wide declines of coral environments has resulted in local and regional vertebrate extinctions. The impact of those extinctions on reef communities, however, remains largely unexplored. Here we show, using a highly resolved model coral reef-seagrass food web, that at least 40 of 188 expected vertebrate species are absent from Jamaican coral reefs. Twenty one of the absent species are of high trophic level and are exploited by humans. The remainder of the absent species are unexploited, and comprises a significantly high proportion of specialized reef foragers. Many of those species are also more trophically specialized than their closest trophic competitors. We conclude that the absence of unexploited species from Jamaica is caused by the overexploitation of high trophic level species, and consequent trophic cascades and secondary extinction among their prey in an increasingly degraded reef environment. The result is a reef community depauperate of both exploited high trophic level predators, and unexploited, specialized lower trophic level reef foragers.