Transient Component Research Articles

Reweighted Dual Sparse Regularization and Convex Optimization for Bearing Fault Diagnosis

Performing early and accurate bearing fault diagnosis is of great significance. However, accurate extraction of the repetitive transients from noisy vibration signals is a critical issue. In this article, a reweighted dual sparse regularization (RDSR) method is proposed for bearing fault diagnosis, and the RDSR is a unified framework of the reweighted generalized minimax-concave (reGMC) penalty and the ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -norm regularization. To be specific, the reGMC penalty and ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -norm are both introduced in the sparse coding model. The reGMC is utilized to enhance the sparsity and overcome the underestimation deficiency of the ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -norm while restraining the interference. Moreover, the ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -norm is employed to simplify the model and overcome the overfitting problem, which can make the optimization process rapid and stable. Therefore, it can observably enhance the accuracy of bearing fault diagnosis and preserve the amplitude of the fault transient component. Comparisons with ℓ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -norm minimization model and the conventional spectral kurtosis (SK) show that the proposed method can preserve the spectral peak of the periodic transient components and improve the signal-to-noise ratio (SNR). Experimental case studies further verify that the proposed method can accurately estimate the periodic transient component from vibration signals, which demonstrates that the proposed method is feasible for bearing fault diagnosis.

Mechanism of second harmonic generation of photovoltaic grid-connected system faults and its impact on transformer protection

The short-circuit transient characteristics of photovoltaic(PV) power system are different from traditional power sources. When the grid voltage drops, the output current of PV will contain a high proportion of second harmonics which cannot be ignored. This paper takes a single-phase turn-to-turn short-circuit fault inside the PV grid-connected transformer as an example. First, it analyzes the mechanism of single-frequency input and double-frequency output of a three-phase grid-connected inverter based on a phase-locked loop (PLL), and secondly, considering the comprehensive grid-connected control strategy, the principle of current second harmonic in the minor faults is analyzed and the analytical expression of second harmonics is derived. It is pointed out that the transient dc component will produce second harmonic component in the grid-connected current through control system of the inverter. This current induces a second harmonic voltage in the impedance, and as a disturbance term it generates a new harmonic current through the control link. Superimposed second harmonic currents in two scenarios may threaten the reliability of transformer differential protection. Finally, the correctness of the theoretical analysis is verified by simulation based on MATLAB/Simulink.

Generic Dynamic Phase-Shift Control for Bidirectional Dual-Active Bridge Converters

This letter proposes a generic method to model and mitigate the transient dc bias in the transformer winding current and the magnetizing flux linkage of the dual-active bridge (DAB) converter, which is valid for all the most commonly used modulation methods such as single phase-shift, extended phase-shift, dual phase-shift, and triple phase-shift. By performing a simple dynamic volt-seconds balancing in each half-bridge independently, the transformer winding current and the magnetizing flux linkage can reach any new reference steady state in half-switching cycle simultaneously with significantly suppressed transient dc-bias components. More importantly, this excellent dynamic performance can be realized for any modulation mode transition, regardless of the dc voltage ratio and the power direction change. Comprehensive simulations and experiments are performed to validate the effectiveness of the proposed control method.

Intelligent Defect Identification Based on PECT Signals and an Optimized Two-Dimensional Deep Convolutional Network

Accurate and rapid defect identification based on pulsed eddy current testing (PECT) plays an important role in the structural integrity and health monitoring (SIHM) of in-service equipment in the renewable energy system. However, in conventional data-driven defect identification methods, the signal feature extraction is time consuming and requires expert experience. To avoid the difficulty of manual feature extraction and overcome the shortcomings of the classic deep convolutional network (DCNN), such as large memory and high computational cost, an intelligent defect recognition pipeline based on the general Warblet transform (GWT) method and optimized two-dimensional (2-D) DCNN is proposed. The GWT method is used to convert the one-dimensional (1-D) PECT signal to a 2D grayscale image used as the input of 2D DCNN. A compound method is proposed to optimize the baseline VGG16, a well-known DCNN, from four aspects including reducing the input size, adding batch normalization layer (BN) after every convolutional layer(Conv) and fully connection layer (FC), simplifying the FCs, and removing unimportant filters in Convs so as to reduce memory and computational costs while improving accuracy. Through a pulsed eddy current testing (PECT) experiment considering interference factors including liftoff and noise, the following conclusion can be obtained. The time-frequency representation (TFR) obtained by the GWT method not only has excellent ability in terms of the transient component analysis but also is less affected by the reduction of image size; the proposed optimized DCNN can accurately identify defect types without manual feature extraction. And compared to the baseline VGG16, the accuracy obtained by the optimized DCNN is improved by 7%, to about 99.58%, and the memory and computational cost are reduced by 98%. Moreover, compared with other well-known DCNNs, such as GoogLeNet, Inception V3, ResNet50, and AlexNet, the optimized network has significant advantages in terms of accuracy and computational cost, too.

Impact of DFIG‐based wind turbine's fault current on distance relay during symmetrical faults

As a new highly penetrated power source of modern power systems, doubly fed induction generator (DFIG)-based wind turbine (WT) has a different fault current contribution when compared with a synchronous generator. DFIG-based WT's fault current has significant impacts on distance relay's performances and may result in maloperation. In this study, the impacts of DFIG-based WT's fault current on the dynamic performances of two typical distance protection elements, mho and polarisation, are studied in terms of EMTP simulations and fault current expressions in symmetrical fault scenarios. It is discovered that the zone-1 distance relays of the lines connecting to DFIG-based wind power plants tend to overreach. Also, the following analysis indicates that the transient components of DFIG-based WT's fault current and the phasor estimation unit are the underlying reasons. With those understanding, this study is expected to help design new setting methods and for distance protection in power systems integrating wind power plants to prevent this kind of possible overreach.

Development and validation of a TRNSYS type to simulate heat pipe heat exchangers in transient applications of waste heat recovery

Heat pipe heat exchangers (HPHEs) are being more frequently used in energy intensive industries as a method of low-grade waste heat recovery. Prior to the installation of a HPHE, the effect of the heat exchanger within the system requires modelling to simulate the overall impact. From this, potential savings and emission reductions can be determined, and the utilisation of the waste heat can be optimised. One such simulation software is TRNSYS. Currently available heat exchanger simulation components in TRNSYS use averaged values such as a constant effectiveness, constant heat transfer coefficient or conductance for the inputs, which are fixed during the entire simulation. These predictions are useful in a steady-state controlled temperature environment such as a heat treatment facility, but not optimal for the majority of energy recovery applications which operate with fluctuating conditions. A transient TRNSYS HPHE component has been developed using the Effectiveness-Number of Transfer Units (ɛ-NTU) method and validated against experimental results. The model predicts outlet temperatures and energy recovery well within an accuracy of 15% and an average of 4.4% error when compared to existing experimental results, which is acceptable for engineering applications.

Persistent and transient inefficiency in adult education

This paper evaluates the inefficiency of adult education programs. Using an advanced four-component stochastic frontier model on Belgian adult education data, we distinguish between persistent and transient inefficiency of adult education programs. Whereas persistent inefficiency is structural and difficult to tackle because of its time-invariant nature, transient inefficiency can be eliminated somewhat easily without a major structural change. Thus, reduction in different inefficiency components may require different policy measures. Our results indicate that despite the presence of persistent inefficiency, the overall inefficiency is mainly driven by the transient component, and hence, at the control of the adult education management. The findings suggest that social interaction is relevant in adult education as both more sessions and more learners per program increase educational efficiency. Moreover, adult education programs seem to be particularly useful for young less-educated learners.

Influence of the probe dimensions on the display of the low-frequency dispersion of the earth’s electromagnetic properties for measure-ments in marine waters up to 100 m deep

The purpose of the study is to show the effect of the probe dimensions on the display of the low-frequency dispersion of the geological formations’ electromagnetic properties in transient measurements by electric lines in the axial area of the source for the water areas up to 100 m deep. The study analyzes the change in the transient signal, the finite difference, and the transform (the ratio of the above two) as a function of the length of the source (a horizontal grounded electric line (AB) 50 to 2,000 m), the receiver (a three-electrode electric line (MON) 50 to 2,000 m), and the distance between their centers (spacing) 100 to 4,000 m. The values obtained from the conductive and conductive polarizing models are compared for the identical probes installed at the same depth. The grounded electric line is located within the conducting medium with a conductive polarizable base. The conducting medium is associated with the seawater thickness in the marine shelves up to 100 m deep. The conductive polarizable base is a geological environment (earth) covered with a layer of water. The polarizability of the base is registered by introducing frequency-dependent electrical resistivity by the Cole-Cole formula. The calculations show the display of different transient components associated with the transient buildup and the earth’s low-dispersion properties caused by both galvanic and eddy currents. These components manifest themselves differently for the probes with different dimensions of the source line, receiving line, and spacing. Based on the calculations, it can be argued that in the time range from 1 ms to 16 s, at the probes that have different dimensions and are immersed in the water layer up to 100 m thick, the signal changes depending on the immersion depth for “small” installations (AB of 50 and 100 m), while there is no such dependence for the rest of the probes used in the calculations (AB of 250, 500, 1,000, and 2,000 m).

Advanced Materials and Systems for Biodegradable, Transient Electronics.

Transient electronics refers to an emerging class of advanced technology, defined by an ability to chemically or physically dissolve, disintegrate, and degrade in actively or passively controlled fashions to leave environmentally and physiologically harmless by-products in environments, particularly in bio-fluids or aqueous solutions. The unusual properties that are opposite to operational modes in conventional electronics for a nearly infinite time frame offer unprecedented opportunities in research areas of eco-friendly electronics, temporary biomedical implants, data-secure hardware systems, and others. This review highlights the developments of transient electronics, including materials, manufacturing strategies, electronic components, and transient kinetics, along with various potential applications.

Faulty Feeder Detection Method Based on VMD–FFT and Pearson Correlation Coefficient of Non-Power Frequency Component in Resonant Grounded Systems

Through analyzing the transient components and transient characteristics in transient zero-sequence current (TZSC), a novel fault feeder detection method based on the transient correlation of non-power frequency components (NPFCs) for the resonant grounded system is proposed. Firstly, using variational mode decomposition combined with fast Fourier transformation (VMD–FFT) to decompose the TZSC, by removing the power frequency components and noise signals, the transient NPFCs can be obtained. Secondly, to reflect the overall changing trend between faulty and healthy currents, the moving average filter is introduced to smooth the NPFCs; in this way, the fault transient features can be accurately revealed. Finally, the faulty feeder can be detected by comparing the threshold with the maximum difference value of comprehensive correlation coefficient of NPFCs. The detection results show that the proposed fault detection method can accurately select the faulty feeder; it is unaffected by fault resistances, fault phase angles, etc. Moreover, the detection method can resist noise interference.

Novel conditional plasmids regulated by chemical switches provide versatile tools for genetic engineering in Escherichia coli

Engineering bacterial genomes or foreign DNA cloned as bacterial artificial chromosomes (BACs) relies on usage of helper plasmids, which deliver the desired tools transiently into the bacteria to be modified. After the anticipated action is completed the helper plasmids need to be cured. To make this efficient, plasmids are used that are maintained by conditional amplicons or carry a counter-selection marker. Here, we describe new conditional plasmids that can be maintained or cured by using chemical induction or repression. Our method is based on the dependency of plasmids carrying ori6Kγ origin of replication on the presence of protein Π. Ori6Kγ based plasmids are tightly regulated conditional constructs, but they require usually special E. coli strains to operate. To avoid this, we placed the Π protein expression under the control of a co-expressed conditional repressor. Regulating the maintenance of plasmids with administration or removal of chemicals is fully compatible with any other conditional amplicons applied to date. Here, we describe methods for inducing sites specific recombination of BACs as an example. However, the same strategy might be used to construct appropriate helper plasmids for any other transient components of genome editing methodologies such as λred recombinases or CRISPR/Cas components.

Research of the transient processes for discrete control systems

The dynamic characteristics of discrete systems, as in the theory of continuous systems, include transfer functions, time (impulse, transient) and frequency characteristics. When determining time characteristics, a single discrete impulse and a single discrete function are used as typical signals. The transient characteristic of a linear discrete system is the response to the single discrete function under zero initial conditions. The study of discrete systems begins with an assessment of their fundamental operability, that is, stability. The stability of continuous linear systems is determined by the behavior of the transient component of the general solution of a homogeneous differential equation of the system under study. Similarly, the problem is solved for discrete systems described by linear difference equations. A discrete system is called stable if the transient process tends to zero over time. The analysis of the discrete control system on the stability and accuracy of the transient process is conducted. Conclusion: in a discrete system stability, accuracy and control quality depend on the parameters of the gain system and the time.

Water vapour transport changes associated with the interdecadal decrease in the summer rainfall over Northeast Asia around the late‐1990s

AbstractThis study reveals an obvious interdecadal change in the summer water vapour budget over Northeast Asia around the late‐1990s accompanied with the abrupt rainfall decrease. After the late‐1990s, water vapour transported into Northeast Asia is apparently reduced under control of a local anomalous anti‐cyclone. The water vapour transport is further explored by decomposing the water vapour flux into stationary and transient components, which are associated with the mean flow and transient eddy, respectively. The results indicate that the stationary component accounts for nearly 84% of the total water vapour budget change, much larger than the contribution from the transient component (16%). The correlation coefficient between the interdecadal variation of net and stationary (transient) water vapour budget is 0.95 (0.14). Hence, the stationary term plays a dominant role in contributing to interdecadal change in the total water vapour transport. In addition, change in the water vapour budget over Northeast Asia around the late‐1990s is primarily attributed to the wind field change at the lower troposphere. A further comparison of the water vapour budgets in four boundaries of Northeast Asia shows that the water vapour budgets via the southern and northern boundaries display remarkable changes around the late‐1990s, exerting significant influences on the total moisture budget change. The anomalous atmospheric water vapour transport circulations in association with the southern and northern boundaries both present a wave‐like teleconnection pattern over the Eurasia, whose formation may be partly due to the combined impacts from the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation.

IMPROVING THE EFFICIENCY OF FAULT PROTECTION SYSTEMS OF ELECTRICAL GRIDS BASED ON ZERO SEQUENCE VOLTAGES AND CURRENTS WAVELET TRANSFORMS

Introduction. A significant proportion of earth faults in medium voltage networks represents a short-lived and transient process. Problem. In such cases, earth fault protection that responds to steady-state current and voltage is not able to operate properly. Purpose. To develop earth faults protection selective algorithm using transient components, that occur in zero-sequence currents and voltage in the fault process. Method. A mathematical model of the power supply system was applied to study the transient components of currents and voltage of zero sequence in compensated electrical networks with phase-to-earth faults, and a those model also is used to test the operation of the developed protection algorithm. The results showed that, the reactive power for transient components, of the frequency greater by 4-6 times, than fundamental frequency, which are extracted from the current and voltage of zero sequence by wavelet transform in compensated electrical networks on the damaged feeder, is positive regardless of the degree of compensation of the capacitive current. That may be the basis of the principle of directional protection. Originality. Phase-to-earth fault selective protection algorithm has been developed. In that algorithm, first derivatives of currents and voltages of zero sequence are found, to reduce the influence of aperiodic components. And then, by using of the wavelet transform with Morlet mother function, an orthogonal components are extracted from them. Reactive power is calculated for transient component. If that reactive power excess of threshold, the relay will make a decision. The reliability of the developed protection algorithm is confirmed by the results of mathematical modelling and verification of the test sample at the laboratory stand and by means of field signals that were recorded by digital loggers at the substations.

Modeling of DC Distribution System Based on High Frequency Transient Components

The fault characteristics of multi-converter DC system are complex and variable. How to use fault transient information for fault characteristic analysis and protection setting is one of the challenges faced by the development of DC power distribution system. In this article, the high-frequency characteristics of faults in DC systems are analyzed. Then based on the transient fault circuit analysis method, the frequency domain impedance model of typical converters is obtained. The model established in the higher frequency band is not affected by the control strategy and can provide a stable impedance value, which lays a theoretical foundation for the protection principle. At the same time, the characteristics of the high frequency impedance superposition of multi-converter system are also given, which provides a basis for system-level protection setting and coordination. Finally, the DC power distribution system model is established in PSCAD/EMTDC for simulation, and the results prove the accuracy and validity of the DC system model.

Rolling Bearing Fault Feature Extraction Based on Adaptive Tunable Q-Factor Wavelet Transform and Spectral Kurtosis

The fault feature of the rolling bearing is difficult to extract when weak fault occurs and interference exists. The tunable Q-factor wavelet transform (TQWT) can effectively extract the weak fault characteristic of the rolling bearing, but the manual selection of the Q-factor affects the decomposition result and only using TQWT presents interference. Aiming at the above problems, an adaptive tunable Q-factor wavelet transform (ATQWT) and spectral kurtosis (SK) method is proposed in this paper. Firstly, the method applies particle swarm optimization (PSO) to seek the optimized Q-factor for avoiding manual selection, which uses the kurtosis value of the transient impact component as the particle fitness function. The rolling bearing fault signal is decomposed into continuous oscillation component and transient impact component containing fault feature by the optimized Q-factor. Then, due to the presence of interference in the decomposition result of ATQWT, the SK analysis of the transient impact component is used to determine the frequency band of periodic impact component characterizing fault feature by fast kurtogram. Finally, the band-pass filter established through the above frequency band is employed to filter the interference in the transient impact component. Simulation and experimental results indicate that the ATQWT can highlight the periodic impact component characterizing rolling bearing fault feature, and the SK can filter interference in the transient impact component, which improves feature extraction effect and has great significance to enhance fault diagnosis accuracy of the rolling bearing. Compared with EEMD-TQWT and TQWT-SK, the fault feature extracted by the proposed method is prominent and effective.

Extraction and analysis of transient signals of a deployable structure vibration based on the sparse decomposition with mixed norms

This contribution deals with extraction and analysis of the transient component of a deployable structure vibration based on the sparse decomposition with mixed norms. The transient component is a critical nonlinear dynamical characteristic of the deployable structure. However, extraction of weak transient signals has always been a challenging problem in signal processing. To resolve this problem, we present an algorithm based on the sparse decomposition with the mixed norm. As redundant components may occur in the sparse decomposition, resulting from the end effect of time-frequency representations. Flip mirror extension is designed to address this question. The feasibilities of the short time Fourier transform, the Wigner-Ville distribution, the ensemble empirical mode decomposition, the stationary wavelet transform and the presented method to catch the transient component are verified with a sample example, and the result shows that the presented algorithm is more powerful. After that, the method is employed to extract transients from experimental signals of a deployable structure model; furthermore, characteristics of these components are analyzed, and are as follows: the transient components are complicated; the transient amplitudes decrease as a whole; the transient amplitudes are locally random. The algorithm is valuable for extracting the transient component from the vibrations, and the analysis may be valuable for the analysis of the nonlinear dynamics of the deployable structure.

Persistent and resurgent Na+ currents in vestibular calyx afferents.

Vestibular afferent neurons convey information from hair cells in the peripheral vestibular end organs to central nuclei. Primary vestibular afferent neurons can fire action potentials at high rates and afferent firing patterns vary with the position of nerve terminal endings in vestibular neuroepithelia. Terminals contact hair cells as small bouton or large calyx endings. To investigate the role of Na+ currents (INa) in firing mechanisms, we investigated biophysical properties of INa in calyx-bearing afferents. Whole cell patch-clamp recordings were made from calyx terminals in thin slices of gerbil crista at different postnatal ages: immature [postnatal day (P)5-P8, young (P13-P15), and mature (P30-P45)]. A large transient Na+ current (INaT) was completely blocked by 300 nM tetrodotoxin (TTX) in mature calyces. In addition, INaT was accompanied by much smaller persistent Na+ currents (INaP) and distinctive resurgent Na+ currents (INaR), which were also blocked by TTX. ATX-II, a toxin that slows Na+ channel inactivation, enhanced INaP in immature and mature calyces. 4,9-Anhydro-TTX (4,9-ah-TTX), which selectively blocks Nav1.6 channels, abolished the enhanced INa in mature, but not immature, calyces. Therefore, Nav1.6 channels mediate a component of INaT and INaP in mature calyces, but are minimally expressed at early postnatal days. INaR was expressed in less than one-third of calyces at P6-P8, but expression increased with development, and in mature cristae INaR was frequently found in peripheral calyces. INaR served to increase the availability of Na+ channels following brief membrane depolarizations. In current clamp, the rate and regularity of action potential firing decreased in mature peripheral calyces following 4,9-ah-TTX application. Therefore, Nav1.6 channels are upregulated during development, contribute to INaT, INaP, and INaR, and may regulate excitability by enabling higher mean discharge rates in a subpopulation of mature calyx afferents.NEW & NOTEWORTHY Action potential firing patterns differ between groups of afferent neurons innervating vestibular epithelia. We investigated the biophysical properties of Na+ currents in specialized vestibular calyx afferent terminals during postnatal development. Mature calyces express Na+ currents with transient, persistent, and resurgent components. Nav1.6 channels contribute to resurgent Na+ currents and may enhance firing in peripheral calyx afferents. Understanding Na+ channels that contribute to vestibular nerve responses has implications for developing new treatments for vestibular dysfunction.

Edge Computing-Based Fault Location in Distribution Networks by Using Asynchronous Transient Amplitudes at Limited Nodes

The feeders in distribution networks can be generally classified into two types: homogenous and hybrid feeders. Hybrid feeders consist of non-homogeneous line segments. In this paper, a fault location scheme is proposed for distribution grids with both homogenous and hybrid feeders using the edge computing. The standard transient amplitude ratio arrays of the hybrid feeders are first constructed and stored at the edge nodes. Then, an accurate fault location model is trained by the radial basis function neural network and stored in the substation server. To achieve this goal, the transients are first sampled at the measurement nodes and transmitted to the edge nodes nearby. The amplitudes are then extracted to determine the faulty branch. For a hybrid feeder, the actual amplitude ratio array is compared with the standard one to identify the faulty line segment. Finally, the amplitude ratio of the two transient components with different frequencies at one terminal of the faulty section is computed and transmitted to the server. Based on the model of a distribution network built by PSCAD/EMTDC, extensive fault simulations are studied. The results demonstrate the effectiveness of the scheme.

Algorithms for Locating and Characterizing Cable Faults via Stepped-Frequency Waveform Reflectometry

The paper presents algorithms to realize effectively and accurately the stepped-frequency waveform reflectometry (SFWR), i.e. the reflectometric technique based on the use of sinusoidal bursts. This technique is useful for monitoring the health status of connection cables, but has many other applications, like other reflectometric techniques. The paper outlines the theory of SFWR, highlighting the problems associated to the transient components in the reflected signals; presents a method to minimize the effect of the transients, estimating the frequency response function (FRF) of interest with very low systematic error; shows how to use the FRF to locate and characterize faults in cables; evaluates accurately, using simulated cables with exactly known characteristics, the errors associated to the proposed methods. Overall, the paper demonstrates how the SFWR technique can be effectively used for testing cables, and in general determine, via reflectometry, parameters of interest of transmission lines.