Current Waveform Parameters Research Articles

Critical comparison of potential machine learning methods for lightning thermal damage assessment of composite laminates

The present study assesses the potential of using machine learning (ML) methods to predict the extent of lightning thermal damage in fiber-reinforced composite laminates using three supervised machine learning (SML) algorithms: (1) linear regression (LR), (2) decision tree (DT)-based, and (3) MLP models. These models were based on the 10 most significant factors that influence the severity of lightning damage, including three current waveform parameters, four material configurations, and three orthogonal electrical conductivities of each composite. All models demonstrated good performance with coefficient of determination (R2) values between 0.84 ~ 0.96. The multilayer perceptron (MLP) regression model trained with the lightning matrix damage dataset showed the most promising results (R2 > 0.94). Additional hyperparameter optimization was performed to improve the prediction performance of the baseline MLP model. The hyperparameter optimization (Adam optimizer, tanh activation function, and three hidden layers with 234 neurons) slightly improved the performance of the baseline MLP model by ~0.02, but achieved faster convergence. This result suggests that the baseline MLP model trained with the lightning matrix damage dataset is sufficiently accurate and robust. This paper highlights that ML-informed regression models can serve as an efficient first pass-estimator of lightning matrix damage in composite laminates, potentially reducing the amount of extremely time-consuming and expensive laboratory-scale lightning tests or streamlining the development of complex lightning damage models for future design.

Estimation of lightning overvoltages and critical flashover currents of 150 kV and 400 kV overhead lines: Effects of the CIGRE lightning current waveform parameters

This paper investigates the influence of the CIGRE lightning current waveform parameters on the computation of fast-front overvoltages and critical lightning currents causing flashover of overhead transmission line insulation. The investigation is conducted via ATP-EMTP simulations employing both negative and positive lightning current waveforms corresponding to first return strokes. Typical 150 kV and 400 kV double-circuit overhead lines are evaluated by performing shielding failure and backflashover simulations. The statistical distributions of the parameters required as input for the CIGRE lightning current waveform (front time, maximum steepness, time to half value) are considered in simulations to quantify and analyze their effects; this enables the comparison between negative and positive lightning strikes. The waveform parameters do not affect considerably the critical shielding failure flashover current for both polarities; the most influential parameter in this case is the time to half value. On the other hand, the wavetail duration influences the least the critical backflashover current; the latter is lower for waveforms with faster wavefront (lower front time and higher maximum steepness). The impact of the waveform parameters of positive lightning strikes is more marked for the backflashover case due to their larger variations compared with negative strikes.

Microstructure evolution and mechanical properties of pulse high current diffusion bonding γ-TiAl alloy to Ti2AlNb alloy

The development of lightweight high-temperature materials and their processing methods are receiving increasing attention as the need for improved performance and energy efficiency in aero-engines increase. In this study, the γ-TiAl alloy was successfully soundly bonded to Ti2AlNb alloy by pulsed high current (PHC) diffusion welding. The effect of different high level (HL)/low level (LL) of composite pulse current on the microstructure and mechanical properties of the joints have been studied. The representative interface microstructure of PHC-950 °C TiAl/Ti2AlNb joint was γ-TiAl substrate/diffusion bonding zone/Ti2AlNb impacted zone/Ti2AlNb substrate. The diffusion bonding zone was composed of continuous equiaxed α2 grains and a small amount of B2 and O phases. The α2 phase in the diffusion bonding zone was mainly transformed from the γ phase in γ-TiAl substrate and the B2 and O phase in Ti2AlNb substrate. The composite pulse current has a significant promoting effect on the diffusion of elements and joint formation. The diffusion coefficients of DAl and DNb in hot-pressing (HP, without current effect) diffusion welding joint at interface were 2 × 10−14 m2/s and 0.92 × 10−14 m2/s, respectively. In the representative PHC-950 °C joint with HL/LL = 12/2 cycles (single cycle duration 3.3 ms), diffusion coefficients of DAl-12/2, DNb-12/2 at interface were 19.62 × 10−14 m2/s, 13.34 × 10−14 m2/s, respectively. Increasing the duration of LL would weaken the current effect. The current waveform parameters were tuned to HL/LL = 12/4 and 12/6 cycles, the diffusion coefficients of DAl-12/4, DNb-12/4DAl-12/6 and DNb-12/6 were reduced to 15.69 × 10−14 m2/s, 12.49 × 10−14 m2/s, 15.31 × 10−14 m2/s and 10.99 × 10−14 m2/s, respectively. The PHC-950 °C joints have the highest shear strength of 257.3 MPa at HL/LL = 12/2 cycles, reaching 83.3% of the base material strength. The HP-950 °C TiAl/Ti2AlNb joint has a shear strength of 230.5 MPa, reaching 74.6% of the base material strength. The shear strength of PHC-950 °C joints at HL/LL = 12/4 and 12/6 reduced to 205.3 MPa, 195.8 MPa due to insufficient element diffusion and damages the bonding quality. This work provides a strategy that contributes to reduce the thermal damage of base metal and improve the joint forming efficiency.

Interplay between Anodizing Parameters and Corrosion Resistance of Aluminum-Silicon Alloys

Aluminum alloys are widely used in the automotive, aerospace and construction fields due to their excellent physico-mechanical properties. Nevertheless, the corrosion resistance of bare Al alloys is often insufficient to meet the requirements of several industrial applications and protection strategies are needed. Among these, anodizing is particularly effective since it can lead to the formation of a compact and thick dielectric oxide layer with barrier and corrosion protection capabilities.However, anodizing of highly alloyed Aluminum alloys (e.g. those with an alloy element concentration higher than 5%wt) can be particularly challenging due to the presence of intermetallic precipitates within the Al matrix which generates micro-galvanic coupling events with an associated thickness inhomogeneity of the obtained anodic layer [1].In this context, the work investigates ten new current waveforms for anodizing of Aluminum Silicon alloys (AlSix). Particular attention is devoted to the interplay among waveform parameters (e.g. duty cycle, peak and rest step intensities), oxide layer morphology and corrosion resistance. In particular, metallography, voltammetry and contact angle methods are used in order to correlate different figures of merit with the anodic layer morphological features.It is concluded that a careful optimization of the current waveform parameters can modulate the: a) corrosion current; b) corrosion potential; c) breakdown potential; and d) polarization resistance; of coated specimens. In conclusion, the most effective waveforms are identified and coated Aluminum alloy specimens with a remarkable corrosion resistance are obtained.[1] M Bandiera, A Bonfanti, M Bestetti, F Bertasi, SAE International Journal of Advances and Current Practices in Mobility 3 (2), 973-979.

Study on the Effect of Pulse Waveform Parameters on Droplet Transition, Dynamic Behavior of Weld Pool, and Weld Microstructure in P-GMAW

The heating and impact of arc and droplet acting on the weld pool lead to the transfer of mass, heat, and momentum, which affects the dynamic behavior of the weld pool and the microstructure in the P-GMAW process. In this paper, an image processing program is used to extract the dynamic behavior characteristics of the droplet transition and the weld pool in high-speed photography. The influence of the current waveform on the arc pressure and the impact of the droplet is quantitatively analyzed with different parameters. The dynamic behavior of the weld pool and the microstructure under different current waveform conditions are further studied. The internal relation of current waveform parameters to weld pool behavior and weld microstructure was expounded. The results show that the droplet impact is positively correlated with the pulse peak current. The rectangular wave pulse has a more significant droplet impact than the exponential wave with the same waveform parameters. The impact of droplet transition on the weld pool enhances the convective intensity of the weld pool. It slows down the cooling rate of the solidified weld microstructure below the tail of the weld pool, increasing the grain size of the weld microstructure.

Differences Between Currents of Triggered Lightning Striking the Distribution Line and the Ground

In this paper, the initial stage and the return stroke current waveform parameters of rocket-triggered lightning flashes to the ground and to the distribution line have been analyzed. The results show that the average current, the charge transferred and the action integral associated with the Initial Stage with return strokes are greater than the corresponding values without return strokes. For the initial stage, the presence of the distribution line greatly reduces the maximum current, average current, charge transfer, and action integral by a factor of 0.35, 0.42, 0.51, and 0.19, respectively. For the return stroke, the presence of the distribution line has little effect on the other parameters except for a 2.4-fold increase in the 10-90% risetime. The presence of the distribution line affects the initial stage parameters more significantly than the return stroke parameters, probably because the lightning channel equivalent impedance of the initial stage is much smaller than that of the return stroke. The lightning channel equivalent impedance of the initial stage estimated in this paper is about 145 ohms and the estimated lightning channel equivalent impedance for the return stroke is greater than 2000 ohms.

Short-Circuit Fault Current Parameter Prediction Method Based on Ultra-Short-Time Data Window

The prediction of short-circuit current parameters is essential for the adoption of short-circuit fault limiting techniques and the reliable cut-off of circuit breakers. In order to quickly and accurately predict the short-circuit current waveform parameters, a short-circuit fault current prediction method based on ultra-short-time data windows (UDWs) is proposed. First, a mathematical model for describing short-circuit faults is constructed and the characteristics of short-circuit currents are analyzed. Then, the principle of the UDW method for predicting short-circuit current waveform parameters is derived, the correctness of the principle is verified by setting-up an ideal signal through simulation, and the exponential and linear expressions fitted to the curve are analyzed and compared with the improved half-wave Fourier method for predicting current parameters. Finally, trend filtering technology is proposed to eliminate high-frequency interference and white noise interference. The results show that the ultra-short-time data window method can quickly and accurately predict the short-circuit current waveform parameters, where the exponential expression is a better fit to the waveform, and the trend filtering technique enables the elimination of high-frequency and white noise interference in the initial stages of prediction.

Excitation Temperature Imaging of Vacuum Arc Based on Two-Line Radiance Method

The excitation temperature of the high-current vacuum arc was measured based on the intensity ratio of two Cu I spectra of 510.6 and 515.3 nm. Diffuse mode vacuum arcs with the peak current of 2 kA, igniting between 5-mm gap, 10-mm phi electrodes, Cu100, Cu80Cr20, and Cu50Cr50 wt.% contacts were measured by a multiple-imaging optical system and high-speed video camera. It turns out that the excitation temperature was almost evenly distributed in the gap. The excitation temperature at the current peak depended on the electrode material and took higher in the order of Cu100, Cu80Cr20, and Cu50Cr50. The excitation temperature was also measured by a spectroscopic approach, and it showed the same tendencies as the measurement using multiple-imaging optical systems and a high-speed video camera. The current decreasing phase of dc interruption was simulated by using semiconductor switches at the peak of ac 50-Hz current, and as a result, the current zero with a decreasing ratio of 30 A/μs was realized. The excitation temperature for the Cu100 electrode decreased with the decreasing current, whereas those for Cu80Cr20 and Cu50Cr50 increased. This difference suggests that developing direct current vacuum circuit breakers needs the optimization of the electrode materials, current waveform, and plasma parameters in the gap.

Study on Operation Parameter Characteristics of Induction Filter Distribution Transformer in Low-Voltage Distribution Network

There is a need for induction filter technology in the field of low-voltage distribution networks. This paper proposes an induction filter distribution transformer with a unique Dd0yn11 three-winding configuration. This approach allows for the control of load side harmonics in low-voltage distribution networks. At present, the induction filter technology proposed in the known literature is mostly used in the high-voltage power system, but there is still no research on the application of induction filter technology to the distribution transformer with Dyn11 under the low-voltage distribution network. In this paper, the wiring scheme of inductive filter distribution transformer and filter system in low-voltage distribution network is established firstly, then the mathematical relationship between the harmonic current generated by the load side and the current on the grid side is derived according to the winding model, and it can be deduced that the induction filter distribution transformer with its filtering system has good filtering performance and reactive power compensation characteristics. Finally, the experiment simulates the three-phase harmonic load, detects the current waveform and other parameters of the actual grid side of the new transformer, verifies the correctness of the theoretical analysis. The induction filter distribution transformer proposed in this paper provides a new solution for harmonic suppression and reactive power compensation in low-voltage distribution network, which fills the vacancy of the application of induction filter technology in low-voltage distribution network, This paper reveals that the inductive filter technique has a good filtering performance when applied to low-voltage distribution network. And it provides a reference for further research on improving power grid efficiency, saving energy cost and improving transformer electromagnetic environment under low-voltage distribution network.

The Coatings Breakdown Products Influence on the Gas Metal Arc Welding Parameters

The installation and renovation works of steel structures are often performed using gas metal arc welding. Thereby, the welded elements of these structures are frequently protected by a variety of primers and coatings, especially in shipbuilding. Complex nonequilibrium physical and chemical processes occurring under the influence of high temperatures and electric arc discharge, as well as the presence of the products that affect the welding parameters, have a significant impact on the joints’ quality. Experimental studies on the coatings’ breakdown products influence on the gas metal arc welding parameters were performed with epoxy, alkyd, polyacrylate, polyvinyl butyral primers, epoxy zinc filled, vinyl chloride, vinyl isobutyl, and organosilicate coatings. The peculiarity of welding current waveform parameters was studied using oscillograms processing. It was found that the main coatings breakdown products that influence the current waveform are oxygen and carbon monoxide.

Experimental investigation of the repeatability of direct damage induced by lightning strikes on metallic panels

Metallic parts of aircrafts that are used for fuel tanks areas or even for the fuselage can suffer from severe direct damage due to lightning strikes. Laboratory tests imitating lightning strikes follow standard regulations requirements that prescribe the current waveforms the structure must resist depending on the zone of the airplane. D+B+C* current waveforms are under concern here and are reproduced in by specific current delivery devices at DGA-Ta lightning lab. The present paper points out that in some cases, tests considered as identical from the standard regulation point of view can generate different damages in the plate, and even variability in perforation apparition. This paper proposes a damage severity index (DSI) that allows considering in an intrinsic manner the effect of the testing parameters related to the current waveform or from the sample modification. The analysis of the tests exhibits a threshold over which a critical crater occurs and the risk of perforation is maximal. We use the DSI to perform a sensitivity analysis on a small data set of lightning tests and quantify the positive or negative effects of significant current waveform or sample input parameters.

Characterization of high-current pulsed arcs ranging from 100–250 kA peak

In this paper, we present the laboratory study on three experimental setups that produce a free arc channel subjected to the transient phase of a lightning current waveform. This work extends the high-current pulsed arc characterization performed in previous studies for peak levels up to 100 kA. Eleven high-current waveforms with peak value ranging from 100–250 kA with different growth rates and action integrals are studied, allowing the comparison of different test benches. These waveforms correspond to standard lightning ones used in aircraft certification processes. Hydrodynamic properties such as arc channel evolution and shock-wave propagation are determined by high-speed video imaging and the background-oriented Schlieren method. The arc diameter reaches around 90 mm at 50 μs for a current of 250 kA peak. Space- and time-resolved measurements of temperature, electron density and pressure are assessed by optical emission spectroscopy associated with the radiative transfer equation. It is solved across the arc column and takes into account the assumption of non-optically thin plasma at local thermodynamic equilibrium. For a 250 kA waveform, temperatures up to 43 000 K are found, with pressures in the order of 50 bar. The influence of current waveform parameters on the arc properties are analyzed and discussed.

On the radiated EMI current extraction of dc transmission line based on corona current statistical measurements

Corona-originated discharge of DC transmission lines is the main reason for the radiated electromagnetic interference (EMI) field in the vicinity of transmission lines. A joint time-frequency analysis technique was proposed to extract the radiated EMI current (excitation current) of DC corona based on corona current statistical measurements. A reduced-scale experimental platform was setup to measure the statistical distributions of current waveform parameters of aluminum conductor steel reinforced. Based on the measured results, the peak value, root-mean-square value and average value with 9 kHz and 200 Hz band-with of 0.5 MHz radiated EMI current were calculated by the technique proposed and validated with conventional excitation function method. Radio interference (RI) was calculated based on the radiated EMI current and a wire-to-plate platform was built for the validity of the RI computation results. The reason for the certain deviation between the computations and measurements was detailed analyzed.

Single CCD-based sensing of both keyhole exit and weld pool in controlled-pulse PAW

The controlled-pulse strategy is proposed to improve the keyholing stability and dynamics in plasma arc welding (PAW). A cost-effective vision system is developed to acquire both keyhole exit and weld pool images from backside of workpiece in controlled-pulse PAW. With a specially designed optical filter, the images of low-intensity weld pool and high-intensity keyhole exit are obtained simultaneously by one single CCD camera. The dynamic variations of both keyhole exit and weld pool are successfully monitored. The influences of welding current waveform parameters on the dimension and position of keyhole exit and weld pool are measured. The effects of the waveform parameters of the controlled pulse on the establishment/sustainment periods of keyhole exit and the positions of first/last keyhole exits in a pulse cycle are elucidated experimentally.

On Optimal Truncated Biharmonic Current Waveforms for Class-F and Inverse Class-F Power Amplifiers

In this paper, two-parameter families of periodic current waveforms for class-F and inverse class-F power amplifiers (PAs) are considered. These waveforms are obtained by truncating cosine waveforms composed of dc component and fundamental and either second(k=2)or third(k=3)harmonic. In each period, waveforms are truncated to become zero outside of a prescribed interval (so-called conduction angle). The considered families of waveforms include both discontinuous and continuous waveforms. Fourier series expansion of truncated waveform contains an infinite number of harmonics, although a number of harmonics may be missing. Taking into account common assumptions that for class-F PA the third(n=3)harmonic is missing in current waveform and for inverse class-F PA the second(n=2)harmonic is missing in current waveform, we consider the following four cases: (i)n=k=3,(ii)n=3,k=2,(iii)n=k=2,and (iv)n=2,k=3.We show that, in each of these cases, current waveform enabling maximal efficiency (optimal waveform) of class-F and inverse class-F PA is continuous for all conduction angles of practical interest. Furthermore, we provide closed-form expressions for parameters of optimal current waveforms and maximal efficiency of class-F (inverse class-F) PA in terms of conduction angle only. Two case studies of practical interest for PA design, involving suboptimal current waveforms, along with the results of nonlinear simulation of inverse class-F PA, are also presented.

Lightning Strike Ablation Damage Influence Factors Analysis of Carbon Fiber/Epoxy Composite Based on Coupled Electrical-Thermal Simulation

According to the mathematical analysis model constructed on the basis of energy-balance relationship in lightning strike, and accompany with the simplified calculation strategy of composite resin pyrolysis degree dependent electrical conductivity, an effective three dimensional thermal-electrical coupling analysis finite element model of composite laminate suffered from lightning current was established based on ABAQUS, to elucidate the effects of lighting current waveform parameters and thermal/electrical properties of composite laminate on the extent of ablation damage. Simulated predictions agree well with the composite lightning strike directed effect experimental data, illustrating the potential accuracy of the constructed model. The analytical results revealed that extent of composite lightning strike ablation damage can be characterized by action integral validly, there exist remarkable power function relationships between action integral and visual damage area, projected damage area, maximum damage depth and damage volume of ablation damage, and enhancing the electrical conductivity and specific heat of composite, ablation damage will be descended obviously, power function relationships also exist between electrical conductivity, specific heat and ablation damage, however, the impact of thermal conductivity on the extent of ablation damage is not notable. The conclusions obtained provide some guidance for composite anti-lightning strike structure-function integration design.

Propagation Effects on the Electric Field Time Derivatives Generated by the Stepped Leaders and Return Strokes in CG Flashes

In this paper, the effects of propagation over finitely conducting ground on the characteristics of the electric-field time-derivative (dE/dt) pulses, which are generated by the stepped leaders and return strokes in cloud-to-ground (CG) flashes, are investigated. First, a finite-difference time-domain (FDTD) method in two-dimensional (2-D) cylindrical coordinates is proposed. And then, the electric fields produced by different lightning processes are calculated. The current waveform parameters of the stepped leaders are derived based on the MTLE model by trial and error, given the analytical waveform and the measured data at the International Center for Lightning Research and Testing (ICLRT) in Florida, USA. In conclusion, the results demonstrate that the characteristics of the dE/dt pulses, including the peak amplitude, the half-width time, and the 10%-90% rise time, change significantly in propagating over finitely conducting ground. Furthermore, the effects of the parameters (i.e., 10%-90% rise time and half-width time) of the lightning current waveforms on the characteristics of dE/dt pulses are also discussed. The results indicate that the 10%-90% rise time, as compared with the half-width time, has a more significant influence on the characteristics of the dE/dt pulses. Lastly, average energy spectra densities of the simulated dE/dt pulses are calculated, and for comparison purposes, spectral analysis of the data obtained by the very high frequency broadband interferometer are also presented. The theoretical results are consistent with those available experimental data.

Influencing factor analysis based on electrical–thermal-pyrolytic simulation of carbon fiber composites lightning damage

The damage of carbon fiber reinforced polymer (CFRP) laminated composites under lightning strike is analyzed by coupled electrical–thermal-pyrolytic models, which is implemented by the ABAQUS/Standard finite element code coupled with user-defined subroutines USDFLD and HEATVAL. To clarify the effects of the lightning current waveform parameters and the thermal/electrical properties of CFRPs, the damages of CFRP laminated specimens under diverse lightning current waveforms are experimentally and numerically analyzed. The results reveal that the damage volume shows a strong logarithmic relationship with the action integral, and that the damage is strongly governed by the electrical properties of CFRPs, though thermal conductivity variation barely affects the damage volume.

Negative First Return‐Stroke Current Peaks and Impulse Charge Transfer

SUMMARYFor the effective and efficient insulation design of a power line, the return‐stroke current waveform parameters are indispensable. Charge transfer is one of the important parameters when damage to equipment on a power line due to the energy of lightning is discussed. The amount of charge transfer associated with a lightning flash or individual strokes can be estimated by using the electric field change obtained with a slow antenna. The authors observed the electric field waveforms in south Kyushu for the purpose of efficient acquisition of return‐stroke current parameters. In this paper, the authors discuss the relation between the negative first return‐stroke current peaks and the impulse charge transfer based on the observed electric field waveforms.

FDTD Simulation of Insulator Voltages at a Lightning-Struck Tower Considering Ground-Wire Corona

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to the analysis of transient voltages across insulators of a transmission line struck by lightning. In the simulation, three 60-m towers, separated by 200 m, with one overhead ground wire and three-phase conductors are employed. The progression of corona streamers from the ground wire is represented as the radial expansion of cylindrical conducting region around the wire. On the basis of the computed results, the effect of corona discharge at the ground wire on transient insulator voltages is examined. The insulator voltages are reduced by corona discharge on the ground wire. The reduction of insulator-voltage peak due to the ground-wire corona is not very significant: the upper-, middle-, and lower-phase-voltage peaks are reduced by 15, 14, and 13% for a positive stroke with 50-kA-peak and 3-μs-risetime current, and those for the negative stroke with the same current waveform parameters are reduced by 10, 9, and 8%, respectively.