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Being an offline measurement technique, Polarization Depolarization Current (PDC) data is conventionally measured after the oil-paper insulation of the equipment reaches thermal equilibrium. Depending on the condition of the insulation, PDC data measurement time typically ranges from several minutes to few hours. It is understood that atmospheric conditions controls the value of ambient temperature. During field measurement, these conditions may not remain constant throughout the PDC recording process. Variation in ambient temperature disturbs the thermal equilibrium that the equipment may have attained at the start of the measurement procedure. Such a condition invariably affects the recorded dielectric response data. However, methods that are available for analyzing relaxation current assume that temperature equilibrium is maintained throughout the measurement period. Results presented in this paper show that dielectric response data is indeed affected if the ambient temperature increases/decreases monotonically. A method is also proposed in this paper using which the effect of such temperature variation on the recorded relaxation current data can be eliminated. This also ensures correct interpretation of PDC data for condition assessment. Analysis presented shows that the value of the equilibrium temperature does not affect the performance of the proposed technique. The applicability of the proposed methodology is first tested on laboratory samples. Thereafter, it is applied to data collected from a real life power transformer. [ABSTRACT FROM AUTHOR]

Activation energy is popularly used for the estimation of remaining life of transformer insulation. It is defined as the average rate of all reactions that happen with cellulose. Existing literature shows that the activation energy of oil–paper insulation can be obtained from polarization depolarization current (PDC) and return voltage measurement (RVM) data that are measured at a specific temperature. It is practically difficult to ensure the same measurement temperature for both PDC and RVM data. On the other hand, PDC data and its analysis get influenced by de-trapping current. This de-trapping current is generated by ionic charge carriers that get freed from trap sites during PDC measurement process. Formation of these trap sites is related to physical, chemical reactions that happen at oil–paper interface. This paper proposes a methodology which uses de-trapped charge, dislodged from deep and shallow traps, to assess insulation condition and for the prediction of activation energy. Thus, eliminating the need of RVM data. The proposed method is tested using data collected from various real-life in-service transformers. [ABSTRACT FROM AUTHOR]

Utilities prefer to perform a condition-based assessment of power transformer insulation in the least possible shutdown time. It is essential to estimate the values of various insulation condition sensitive performance parameters with higher accuracy. In the present work, a technique for the estimation of performance parameters, moisture content of paper, dissipation factor of the entire oil-paper insulation, paper conductivity, and activation energy is proposed. The evaluation of these parameters using reported techniques requires complete measurement of polarization and depolarization current profile, which requires around 20000 s of measurement time. The present method uses a forecasted polarization current profile obtained from 600 s of measured polarization current data. Detrended Fluctuation Analysis is applied to the forecasted polarization current data obtained from various in-service power transformers to obtain a suitable parameter. It is shown that this parameter maintains well-defined relationships with parameters; moisture content of paper, dissipation factor of oil-paper insulation, paper conductivity, and activation energy. The proposed technique is beneficial for utilities as it eliminates the requirement of measuring depolarization current and return voltage measurement for estimating activation energy. [ABSTRACT FROM AUTHOR]

Transistor random threshold voltage variations due to process fluctuations seriously affects the stability of Static Random Access Memory (SRAM). In this paper, a SRAM bit transistors threshold voltage $({Vth})$ deviation monitoring scheme and system is proposed. This scheme ingeniously achieves on-chip measurement of all transistors threshold voltages without altering compact SRAM bit array layout. Control signal strategies and Transistor ${Vth}$ Determination Circuit (TVDC) for different types of Devices Under Test (DUTs) have been proposed. The system is implemented using a 65 nm CMOS process with a core area of 0.01875mm2. Through Monte Carlo analysis, the Weighted Average (WA) difference of the proposed scheme and the direct measurement method is not more than 10mV, and the Root Mean Square Error (RMSE) difference is not more than 3mV. This system can also effectively detect the cell position of the transistor threshold voltage mismatch simulated by modifying the substrate voltage. For SRAM arrays of different scales, the method proposed in this paper has area efficiency and flexible reconfigurability. [ABSTRACT FROM AUTHOR]

The simulation of electric field transients in HVDC cables can be a fundamental tool to support insulation system design when operation dynamics, which includes voltage polarity inversions and load variation, becomes significant during the expected cable life. The field behavior during voltage and temperature transients is associated with intrinsic and extrinsic ageing processes that can affect the cable design life. Traditional models employed for electric field simulations consider only the non–linear, steady–state dependence of conductivity on temperature and field magnitude, but they neglect the transient behavior of permittivity and conductivity, that is, polarization and charge trapping phenomena. These processes impact on the duration of the field transient and thus ageing. This paper discusses the numerical implementation of an electro–quasistatic model that can be used to perform transient simulations of electric fields in HVDC cables insulation. With respect to the model traditionally employed, the presented one is extended with Debye's equations for dielectric polarization processes. The model is implemented numerically using finite differences, or the Occhini equivalent circuit: this paper demonstrates that the two approaches are equivalent. Numerical simulations show that, during transients, polarization processes slow down the electric field dynamics and reduce its maximum intensity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents an online method to monitor the conditions of the substation grounding grid. The proposed method utilizes phase-to-ground faults occurring in downstream feeders as test current sources and the neutral of a specially selected feeder as the electrode for GPR (ground potential rise) measurement. The measured fault currents and GPRs are then used to estimate substation grounding grid impedance. The method, once established, can monitor the grounding grid impedance continuously and automatically, and the trend of the impedance change can be observed. As a result, the proposed method can yield much more reliable information on the substation grounding conditions. The method also overcomes many disadvantages of the offline methods. The proposed idea, algorithm, and hardware setup are described in the paper. Factors contributing to measurement errors are investigated in detail. [ABSTRACT FROM AUTHOR]

This paper focuses on the current distribution and AC loss of BSCCO/REBCO hybrid tapes. Based on their geometry and E-J character of superconductors, a one-dimensional model is established to compute the current distribution and AC loss under an AC operating current in self-magnetic field. The current distributions of hybrid tapes with different number of REBCO tapes and one BSCCO tape are studied. The numerical and experimental results are in good agreement. According to the current distribution characteristics, AC loss of each tape in the hybrid tape is analyzed and calculated. AC losses of 3 kinds of hybrid tapes are measured and discussed. The method proposed in this paper for AC loss simulation is quite effective for hybrid tapes composited by two or more types of superconducting tapes. [ABSTRACT FROM AUTHOR]

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

The physical mechanisms involved in the trapping and de-trapping processes associated with surface donor traps in gallium nitride (GaN) transistors are discussed in this paper. The paper challenges the conventional transient techniques adopted for extrapolating the trap energy level via experiments and TCAD simulations. Transient TCAD simulations were employed to reproduce the time-dependent electrical behavior of a metal-on-insulator field-effect transistor and explain the influence of the electric field and energy barrier on the transient time associated with the trapping and de-trapping mechanisms of surface traps. The comparison between three test structures and the relative variation of the trapping and de-trapping times with the bias and trap parameters leads to the suggestion of a proposed test structure and bias configuration to accurately extrapolate the energy level of surface traps in GaN transistors. [ABSTRACT FROM AUTHOR]

For achieving the aging characteristic parameters of transformer oil-paper insulation, oilimpregnated pressboard samples are acceleratedly thermally aged at high temperature (~ 150 °C) in laboratory, and on the same sample before and after being aged, polarization and depolarization current (PDC) tests are performed at different temperatures (30, 40, 50 and 60 °C), respectively. Besides analyzing the PDC results, the differential time-domain spectroscopy (DTDS) technique is introduced to investigate the aging status of oil-paper insulation and the influence of measurement temperature. The DTDS parameters such as polarization component Qn, polarization response time Tn and line-shape parameter αn are extracted with DTDS unscrambling method based on PDC data. It is revealed that DTDS represents similar polarization process and mechanism to PDC, and all the DTDS curves calculated with the obtained parameters Qn, Tn, αn) are in good fit with those measured. By analyzing the effect of temperature and aging, two types of relaxation polarization mechanism are observed, i.e., the interfacial polarizations between oil and paper insulation and inside the pressboard. The polarization components, response speeds and line-shape parameters of both the polarization mechanisms increase evidently on the whole with temperature rising or sample aging. It is demonstrated that, the DTDS theory is suitable for oil-paper insulation material, the DTDS unscrambling method is effective and objective, and such DTDS parameters are sensitive and can quantitatively reflect the changing of temperature and aging condition with regularity. Consequently, the parameters (Qn, Tn, αn) can be considered as the novel characteristic parameters for aging condition estimation of oil-paper insulation to upgrade the application effect of PDC curves. [ABSTRACT FROM PUBLISHER]

In this paper, for the first time, the record high-performance top-gated graphene technology platform is used for electrostatic discharge (ESD) physics exploration while investigating the implications of various design and technology options. Impact of diffusive versus ballistic carrier transport on the failure mechanism in top-gate as well as back-gate graphene FET (GFET) is investigated. A unique contact limited failure in graphene transistors is reported. Physical insights on current saturation in GFET and unique step-by-step failure in dielectric capped transistors are presented for the first time. Moreover, device degradation under ESD timescales and its implications on current saturation are revealed. Finally, the influence of various top-gate designs on the ESD performance is reported. New physical insights and matured GFET technology has eventually enabled record high ESD robustness. [ABSTRACT FROM AUTHOR]

In this paper, a novel technique to improve the fault detection sensitivity in a three-phase transformer using the tank current method is reported. The tank current method was first published by the first author in recent past for single isolated transformer winding. A fault in single isolated transformer winding was uniquely identified employing the typical resonance behavior of tank current, but for three-phase transformer, such implementation is yet to be explored. The present scope of this paper is only for uniformly wound three-phase transformer windings. Implementing the tank current method for such a three-phase transformer may not be very simple, since the neighboring windings, unlike in the case of isolated winding, strongly influence the measurement of the tank current. Therefore, this paper appropriately considers the effect of neighboring windings in a three-phase transformer and investigates the resonance behavior of its tank current to propose a promising innovative extension approach of the method. Experimental results on actual transformers are also presented for practical validation of the proposed method. Results imply that the tank current method is indeed very sensitive to identify the fault in an actual transformer compared to the conventional neutral current method. The authors also believe that the method needs to be reinforced by field measurements on several transformers to ascertain its viability. [ABSTRACT FROM AUTHOR]

Polarization and depolarization current measurements are promising on-site, off-line, non-destructive, non-invasive diagnostic tool for condition assessment of paper-oil insulation of transformers. Interpretation of the results of polarization and depolarization current is complex and hence not practiced as a routine diagnostic method for condition monitoring of transformers. This paper discusses various factors affecting polarization and depolarization current measurements with a deeper insight into the theoretical and practical aspects of this technique. Some of the concerns of PDC measurement are explained with support from simulation and experimental studies on paper oil insulation of a laboratory model transformer. Few case studies are discussed to highlight the difficulties in interpretation of results. [ABSTRACT FROM AUTHOR]

In this response, we show that the paper by Kim et al. by our group has a different research purpose and uses different modeling processes, which was not described in the previous work by Ortiz-Conde et al. The comments issued by Ortiz-Conde et al., who claim that our paper corresponds to a particular case of their previous work, are in our opinion overgeneralized. Differences compared to Ortiz-Conde’s previous work are discussed in detail. We also explain how the problem on threshold voltage pointed out by Ortiz-Conde et al. can be solved through a semiempirical method from measured data. [ABSTRACT FROM AUTHOR]

Ultrasound techniques for flow investigation have been extensively developed for several years. Many methods have reached a level of maturity that allows widespread and still growing clinical use. Recently, new exciting developments have been introduced by the combination of Doppler techniques with advanced (e.g. plane wave) imaging methods. Therefore, a comprehensive review of the current state-of-the-art ultrasound methods applied to flow measurement and imaging becomes relevant. [ABSTRACT FROM PUBLISHER]

This paper presents a novel methodology to estimate the saturation curve parameters of single-phase transformers, using minimum information from inrush and no-load tests. Only the value of the first current peak and the decay time are used from a unique inrush test, and only the third and fifth current harmonics from a unique no-load test. The proposed methodology is based on the existence of a signature for each transformer which can be easily obtained and characterize all possible inrush currents. This is the main contribution of the paper. Different transformers with different parameters have been tested in the laboratory. Experiments and simulations are carried out to validate the methodology. First, the respective no-load and inrush tests are made. Second, the parameters of each transformer are estimated. Third, the performance and accuracy of the proposed methodology are verified by a close agreement between the measured and the estimated saturation curves and between the simulated and the recorded inrush waveforms. Some remarkable advantages of the proposed methodology are: (a) considers the deep saturation, (b) avoids the need to know the residual flux (or to demagnetize the transformer) and the switching angle from the inrush test, and (c) it is computationally straightforward. [ABSTRACT FROM AUTHOR]

The topology and breakpoints of the grounding grid will directly affect its working performance. This paper proposed a resistivity reconstruction method based on magnetic detection electrical impedance tomography (MDEIT) to measure the topology and breakpoints of the grounding grid. First, this paper describes the forward problem of grounding grid detection in MDEIT, and calculates the magnetic-field distribution above the grounding grid. Then, the resistivity reconstruction method based on the least squares method is proposed. Finally, this paper verifies the feasibility of the proposed method by a numerical example, which shows that the proposed method can be applied to measure the topology and breakpoints of the grounding grid. [ABSTRACT FROM AUTHOR]

This paper demonstrates the feasibility of implementing real-time state estimators for active distribution networks in field-programmable gate arrays (FPGAs) by presenting an operational prototype. The prototype is based on a linear state estimator that uses synchrophasor measurements from phasor measurement units. The underlying algorithm is the sequential discrete Kalman filter (SDKF), an equivalent formulation of the DKF for the case of uncorrelated measurement noise. In this regard, this paper formally proves the equivalence of SDKF and the DKF, and highlights the suitability of the SDKF for an FPGA implementation by means of a computational complexity analysis. The developed prototype is validated using a case study adapted from the IEEE 34-node distribution test feeder. [ABSTRACT FROM PUBLISHER]

The performances of a model predictive control algorithm largely depend on the knowledge of the system model. A model-free predictive control approach skips all the effects of parameters variations or mismatches, as well as of model nonlinearity and uncertainties. A finite-set model-free current predictive control is proposed in this paper. The current variations predictions induced by the eight base inverter voltage vectors are estimated by means of the previous measurements stored into lookup tables. To keep the current variations information up to date, the three current measurements due to the three most recent feeding voltages are combined together to reconstruct all the others. The reconstruction is performed by taking advantage of the relationships between the three different base voltage vectors involved in the process. In particular, 210 possible combinations of three-state voltage vectors can be found, but they can be gathered together in six different groups. A light and computationally fast algorithm for the group identification is proposed in this paper. Finally, the current reconstruction for the prediction of future steps is thoroughly analyzed. A compensation of the motor rotation effect on the input voltages is proposed, too. The control scheme is evaluated by means of both simulation and experimental evidences on two different synchronous reluctance motors. [ABSTRACT FROM AUTHOR]

Network parameters error may seriously affect the accuracy of fault location results, even making them unacceptable in extreme cases. This paper proposes a new method that incorporates these errors in wide area fault location problem using phasor measurement units to estimate inaccurate network parameters employing robust state estimation. Our proposed method is composed of two stages. The first stage or the primary stage provides an initial point for the second stage, which is the main contribution of this paper. Additionally, the set of measurements contaminated with bad data could be obtained from the first stage, and its intersection with leverage measurements are then eliminated from the measurement set before feeding it into the second stage. Finally, fault point and faulted line parameters are estimated by the main (second) stage of the method. The proposed method has been applied to two test systems, namely Institute of Electrical and Electronics Engineers (IEEE) 14-bus and IEEE 57-bus systems, to evaluate its accuracy. Simulation results indicate high accuracy and consistency of the proposed method. [ABSTRACT FROM AUTHOR]

As an emerging kinetic damage weapon system, railgun has attracted much attention due to its remarkable advantages such as high initial speed, high kinetic energy, high shooting speed, high emission density, low cost, and antijamming. However, there are currently degradations of electromagnetic railgun launch performance and reliability, the limited service life as well, resulting from rail damage such as the transition erosion and grooving damage. Based on 24 consecutive shots, this paper presents the statistical analysis of B-dot probe data, aiming to show the working stability and reliability of the electromagnetic rail launch system when consecutive firing. On the basis of current data and B-dot probe data, the speed–displacement curve was obtained by simulation, through which it is easy to get the movement state of the armature in the launch track. Finally, by checking the disassembly of the launch rail, this paper analyses the damage states of launching rail after the 24 consecutive launch experiments. Through the above three aspects of research and analysis, this paper could be the reference for the further research and analysis on the performance and lifetime of railgun. [ABSTRACT FROM AUTHOR]

Aging sensitive parameters like dissipation factor, oil and paper conductivity and paper moisture can be estimated from insulation model parameterized using polarization current to assess the condition of transformer insulation. However, polarization current measurement is a time-consuming offline technique. During measurement, variation of environmental conditions (especially temperature) affects the monotonically decreasing nature of recorded data. Analysis of such affected data lead to incorrect conclusion regarding insulation condition. Power transformer being a crucial equipment, utility prefer to reduce its shut down time to minimum amount. In this paper a technique is discussed through which the polarization current measurement time can be reduced significantly. Several transformer data are used for verification of developed method. Presented results show that measurement data corresponding to only 10 minutes is sufficient to estimate the remaining data through the application of discussed method. [ABSTRACT FROM AUTHOR]

Esaki diodes based on interband tunneling have the characteristics of negative differential resistance (NDR) and ultrafast transient time, which lead to broad applications including oscillators, multivalue memories, and terahertz detectors. In this paper, we present the first demonstration of Esaki diodes based on 2-D/3-D heterojunctions—more specifically, chemical vapor deposition MoS2 on degenerately doped silicon. As compared to traditional 3-D heterostructures, these 2-D/3-D heterostructures have the following advantages: dislocation-free 2-D crystals even when the lattices are mismatched, dangling bond-free surface, and capability for large-scale synthesis at low cost. In this paper, monolayer, bilayer, and trilayer MoS2 are synthesized directly on degenerated Si substrate, forming the ultraclean heterostructures without surface contamination from tape and resist. Based on these pristine heterostructures, we are able to observe prominent NDR effect at room temperature. This NDR effect is attributed to the degenerately p-type doping in silicon and the natural n-type doping in MoS2. We also found that the peak voltage corresponding to the local maximum tunneling current depends on the MoS2 thickness. While MoS2 is changing from the monolayer (0.7 nm) to bulk (9.5 nm), the peak voltage increases from 0.8 to 1.6 V. This phenomenon can be explained by the energy-level differences between the monolayer and bulk MoS2. This paper provides the experimental groundwork for the synthesis of transition metal dichalcogenides on degenerately doped Si substrates and opens up new and exciting opportunities for electronic applications of 2-D/3-D heterostructures. [ABSTRACT FROM AUTHOR]

This paper addresses the measurement and calculation of unbalanced magnetic pull (UMP) in a wound rotor induction machine. A new rig for measuring UMP is presented. To our knowledge, this type of rig has not been tested before. This paper details the force calculation method and a method for splitting the UMP and torque. Wound rotor induction machines are now popular as generators in wind turbines. It is important to maintain good operation and low bearing wear, and the UMP in these machines is higher than that of the cage-rotor equivalent because the cage damps the UMP. There is little literature on the UMP in a wound rotor machine. [ABSTRACT FROM AUTHOR]

This is the second of a two-paper series, in which the field-data-based analytical method proposed in Part I has been extended to determine the amount of harmonic currents absorbed by the shunt harmonic filters of the iron and steel (I&S) plants from the rest of the system. The nonlinear characteristics of the plants and the utility are modeled as harmonic current sources, whereas the linear parts of the proposed extended model consist of passive circuit elements, with the harmonic filter $RLC$ circuit parameters also integrated into the model. This extended method, which can be also used for harmonic contribution assessments, requires sample-by-sample time-synchronized harmonic current measurements inside the plants and at the point of common coupling (PCC). It eliminates the need for harmonic voltage measurements at the expense of the need for inside-plant measurements. It has been verified both by computer simulations and by application on field data. The results have shown that the proposed method is a successful tool to determine the magnitude of harmonic currents that are absorbed by the harmonic filters of I&S plants connected to the PCC, particularly when measured harmonic currents of I&S plants exceed the actual contributions. [ABSTRACT FROM AUTHOR]

This paper presents the induced voltage measured at the terminal of a 10 kV distribution line when triggered lightning taking place at a distance of 40 m. It is shown that the induced voltage waveforms exhibit three components including a slow increase preceding the initial negative peak, following a rapid polarity reversal and the attenuated oscillations. The waveform parameters are defined in this paper. The observed negative peak value ranges from −47.1 kV to −7.5 kV. The positive peak value ranges from 5.3 kV to 20.9 kV, and the peak to peak value ranges from 12.8 kV to 63.2 kV. The test results show that the negative peak value of the induced voltage at the terminal of distribution generated by nearby negative triggered lightning generally exceeds the positive peak value, and in some cases the negative peak value even reaches twice the positive peak value. The negative 10%-90% rise time ranges from 2.3 μs to 88.5 μs, and the average oscillation period is about 18 μs. Both negative and positive peaks of induced voltages show good linear relationship with the peaks of lightning return stroke current. [ABSTRACT FROM AUTHOR]

Distribution system state estimation (DSSE) is a core task for monitoring and control of distribution networks. Widely used algorithms such as Gauss–Newton perform poorly with the limited number of measurements typically available for DSSE, often require many iterations to obtain reasonable results, and sometimes fail to converge. DSSE is a non-convex problem, and working with a limited number of measurements further aggravates the situation, as indeterminacy induces multiple global (in addition to local) minima. Gauss–Newton is also known to be sensitive to initialization. Hence, the situation is far from ideal. It is therefore natural to ask if there is a smart way of initializing Gauss–Newton that will avoid these DSSE-specific pitfalls. This paper proposes using historical or simulation-derived data to train a shallow neural network to “learn to initialize,” that is, map the available measurements to a point in the neighborhood of the true latent states (network voltages), which is used to initialize Gauss–Newton. It is shown that this hybrid machine learning/optimization approach yields superior performance in terms of stability, accuracy, and runtime efficiency, compared to conventional optimization-only approaches. It is also shown that judicious design of the neural network training cost function helps to improve the overall DSSE performance. [ABSTRACT FROM AUTHOR]

Detailed physics of the third quadrant electrical characteristics of 1.2-kV rated 4H-SiC accumulation (Acc) and inversion (Inv) channel MOSFETs, based on experimentally measured data and TCAD numerical simulations, are described in this paper for the first time. The power MOSFETs with various channel lengths (0.3, 0.5, 0.8, 1.1 $\mu \text{m}$) used in this paper were fabricated in a 6-in commercial foundry. Numerical simulations verified that there are two current paths in the third quadrant: 1) through the base region and 2) through the p-n body diode. This paper demonstrates that the Acc MOSFETs have a smaller third quadrant knee voltage (${V}_{{\text {knee}}})$ of −1.2 V compared with −1.9 V for the Inv MOSFETs (at ${V}_{g} = {0}$ V and room temperature). Numerical simulations show that this difference is due to a smaller potential barrier for electron transport from the drain to the source in the base region for accumulation channel devices than inversion channel devices. Acc devices are shown to have a lower voltage drop in the third quadrant. [ABSTRACT FROM AUTHOR]

The effects of gamma rays on two kinds of GaN high-electron-mobility transistors (HEMTs) have been investigated in this paper. We have identified a gate degradation using a combination of optical and electrical measurements. We have demonstrated that the channel current under the degradation position is outside of the gate’s control. This degradation prevents the gate from fully pinching off the channel, creating a current concentration region when applying a reverse gate voltage. An integrated analysis, including ${I}$ – ${V}$ characterization, the emission microscope (EMMI) technique, and temperature-dependent measurements, was applied to study its mechanism. It is attributed to an irradiation-induced degradation in the Schottky contact. [ABSTRACT FROM AUTHOR]

For Rogowski coil, as the current carrier passes through the coil center, it fails to locate the lightning current. With the aim of measuring and locating the lightning current at the same time, this paper developed a lightning current sensor. In this paper, the physical model, geometric parameters, and manufacturing process of the lightning current sensor were introduced, and then a novel sensor coil was developed. To verify the reliability of the sensor, experiments were also performed. The good response characteristics of the sensor were also demonstrated. Last but not least, the sensitivity of the sensor was calibrated, and the formula was determined, which demonstrated sensor output voltage and derived by current and distance, providing theoretical and experimental evidence for practical application. [ABSTRACT FROM AUTHOR]

Complexity of sequences plays an important role in pseudorandom sequences and cryptography. In this paper, we present a construction of sequences with high nonlinear complexity from function fields. The main idea is to make use of function fields with many rational places as well as an automorphism of large order. We illustrate our construction through rational function fields and cyclotomic function fields in which there exist some automorphisms of large order. It turns out that we are able to: 1) slightly increase the length of the inversive sequence without losing nonlinear complexity and 2) obtain sequences with much larger nonlinear complexity than random sequences. [ABSTRACT FROM AUTHOR]

This paper presents the newly proposed heating method named “secondary current heating method” to reduce the iron loss on laminated electrical steel sheet cores for high-efficiency electrical motors. It is well known that the magnetic properties of electrical steel sheets, which are used for electrical motor cores, are deteriorated by the residual stress during manufacturing of the electrical motors, and then the iron loss of the laminated electrical steel sheet cores of the electrical motors increases inevitably. The newly proposed secondary current heating method can improve the magnetic properties on laminated electrical steel sheet cores and reduce the iron loss of them in the very short time in comparison with conventional methods. In this paper, the electromagnetic and heating characteristics of the specimens by the proposed method were confirmed, and then it was applied into the laminated cores to reduce iron loss. [ABSTRACT FROM AUTHOR]

Wafer-scale, CMOS compatible graphene transfer has been established for device fabrication and can be integrated into a conventional CMOS process flow back end of the line. In Part I of this paper, statistical analysis of graphene FET (GFET) devices fabricated on wafer scale is presented. Device yield is approximately 75% (for 4500 devices) measured in terms of the quality of the top gate, oxide layer, and graphene channel. Statistical evaluation of the device yield reveals that device failure occurs primarily during the graphene transfer step. In Part II of this paper, device statistics are further examined to reveal the primary mechanism behind device failure. The analysis from Part II suggests that significant improvements to device yield, variability, and performance can be achieved through mitigation of compressive strain introduced in the graphene layer during the graphene transfer process. The combined analyses from Parts I and II present an overview of mechanisms influencing GFET behavior as well as device yield. These mechanisms include residues on the graphene surface, tears, cracks, contact resistance at the graphene/metal interface, gate leakage as well as the effects of postprocessing. [ABSTRACT FROM PUBLISHER]

This paper presents an advanced technique for calculating activation energy of oil-impregnated pressboard through dielectric response current measurement under switching impulse voltage at different temperatures. The proposed technique analyzes the measured impulse voltage and current signals to formulate its equivalent circuit at different temperatures. The equivalent circuit parameters are utilized to determine the shifting of ac conductivity curve along frequency axis with variations in temperatures. Based on the shifted ac conductivity curves at different temperatures, the corresponding activation energy of the insulation is estimated. The effectiveness of the proposed technique is investigated through a few laboratory prepared test samples. [ABSTRACT FROM AUTHOR]

The existing methods for multi-point harmonic contribution evaluation usually require some preconditions, such as the node harmonic current is equivalent to the harmonic emission current and the number of measurements is not less than the number of sources. However, these requirements may not be satisfied in practice. In this context, this paper proposes an improved sparse component analysis (SCA) method to solve the underdetermined blind source separation model, which is used to describe the harmonic state under incomplete measurements. The improved SCA adopts a new two-stage technique. First, the mixing matrix containing harmonic transfer impedances is estimated through the synchrosqueezing S-transform. Then, the source signal vector containing harmonic emission currents is reconstructed through the modified subspace projection. By matching the harmonic impedances and currents, the multi-point harmonic contribution evaluation is further achieved. The efficiency of the proposed method is verified by simulations and field case studies. The results demonstrate that the proposed method outperforms the existing methods in terms of accurately estimating the harmonic emission currents and quantifying the harmonic contributions under incomplete measurements. [ABSTRACT FROM AUTHOR]

In this paper, a self-adaptive protection system is proposed for adjusting the time dial (TD) of reclosers found in electrical power distribution systems (EPDSs). The self-adjustment is carried out in both phase and ground protection. The methodology considers the fuses along the feeder to obtain the fuse-saving philosophy. This feature allows less interference on the protection system already implemented by the electrical power distribution utilities. This methodology also allows using other frameworks, such as the estimation of the fault distance. The software used for computer modeling and simulation was PSCAD™/EMTDC™. The flexibility provided by the method, which allows the incorporation of new logic and changes in decision-making, resulted in an adaptive method with a good performance against different locations, types, and fault impedance. It also resulted in better coordination between the protection devices (PDs). The results compared with well-coordinated conventional protection have shown significant performance gain with the adaptive system. [ABSTRACT FROM AUTHOR]

Fault response of an inverter based resource (IBR) is dictated by its control scheme, making it markedly different from the response of a synchronous source. This has led to misoperation of distance relays when fed by IBRs. Published literature is mostly focused on changing the control design of inverters, but this approach is not practical, as these controls are proprietary and beyond the reach of utilities. To resolve this issue, this paper proposes a method for a source-agnostic distance relay that works in time-domain. Using only single ended measurements, the relay detects, classifies and locates any fault on the line it monitors. The method does not require any polarization technique. It is shown to work for unbalanced lines of any length, for transmission or distribution system with any number (even 100%) of IBRs, is immune to load encroachment, decaying dc offset and prefault currents. With very limited communication, it is also shown to be immune to fault resistance. [ABSTRACT FROM AUTHOR]

In this paper, we study a new variant of trajectory similarity search from the context of continuous query processing. Given a moving object from $s$ s to $d$ d , following a reference route $T_r$ T r , we monitor the trajectory similarity between the reference route and the current partial route at each timestamp for online detour detection. Since existing trajectory distance measures fail to adequately capture the deviation between a partial route and a complete route, we propose a partial trajectory similarity measure to bridge the gap. In particular, we enumerate all the possible routes extended from the partial route to reach the destination $d$ d and calculate their minimum distance to $T_r$ T r . We consider deviation calculation in both euclidean space and road networks. In euclidean space, we can directly infer the optimal future path with the minimum trajectory distance. In road networks, we propose an efficient expansion algorithm with a suite of pruning rules. Furthermore, we propose efficient incremental processing strategies to facilitate continuous query processing for moving objects. Our experiments are conducted on multiple real datasets and the experimental results verify the efficiency of our query processing algorithms. [ABSTRACT FROM AUTHOR]

This paper investigates the voltage profiles and harmonic impacts of high-speed trains on the traction power-supply system (TPSS) and primary utility system. Power-quality (PQ) assessment has become not only a computing tool for TPSS design and planning, but also an indispensable technique for utilities to estimate the accurate PQ impacts from the railway systems. Therefore, to achieve comprehensive PQ assessment in TPSS, a dynamic fundamental/harmonic power-flow (DF/HPF) method is developed in a companion paper, while further application of the technique is described in this paper. The fundamental and harmonic results calculated in a 24-h period, such as loading levels, voltage profiles, unbalance, power loss, and harmonic distortions have been computed. In addition, the statistical measured background harmonics of the utility system are represented by Weibull function and considered in the harmonic evaluation. The unbalance and harmonic impacts are investigated and checked with national standards in this paper. The proposed method can be effective for excavating and predicting the potential serious PQ problems existing in the TPSS by using a train timetable. [ABSTRACT FROM PUBLISHER]

Prior research has shown that autocorrelation and variance in voltage measurements tend to increase as power systems approach instability. This paper seeks to identify the conditions under which these statistical indicators provide reliable early warning of instability in power systems. First, the paper derives and validates a semi-analytical method for quickly calculating the expected variance and autocorrelation of all voltages and currents in an arbitrary power system model. Building on this approach, the paper describes the conditions under which filtering can be used to detect these signs in the presence of measurement noise. Finally, several experiments show which types of measurements are good indicators of proximity to instability for particular types of state changes. For example, increased variance in voltages can reliably indicate both proximity to a bifurcation and the location of increased stress. On the other hand, growth of autocorrelation in certain line currents is related less to a specific location of stress but, rather, is a reliable indicator of stress occurring somewhere in the system; in particular, it would be a clear indicator of approaching instability when many nodes in an area are under stress. [ABSTRACT FROM AUTHOR]

Changes of behavior of earthing systems under high impulse conditions from its steady-state conditions have been found to occur in many studies. There are many factors that are thought to cause these changes. However, little studies so far have been conducted on the effects of earth electrode dimensions and configurations, particularly at field sites. This paper is to present and discuss the results of field site study on the performance of earthing systems of different configurations and dimensions. [ABSTRACT FROM AUTHOR]

Self-integrating Rogowski coil has been widely used for measurements of pulsed currents from nanosecond timescale to microsecond timescale in pulsed power systems. Appropriate designs of coil’s structure are vital to high-frequency response. This paper proposed a new structure of Rogowski coil so as to provide a better response to fast pulsed current. Four Rogowski coils with different structures were tested in three different platforms. Experimental results showed that the hybrid Printed Circuit Board Rogowski coil had the best performance in this paper, which could respond to square waves with fronts of $\sim 2$ ns and had a sensitivity of 0.585 V/kA. The designed maximal peak current was 100 kA. [ABSTRACT FROM PUBLISHER]

The recent power systems literature has witnessed an intensified interest in state estimation methods that can handle a vast array of measurements from large-scale networks while maintaining performance that is commensurate with real-time requirements. When measurements are from the Supervisory Control and Data Acquisition (SCADA) system and Phasor Measurement Units (PMUs), an elegant formulation of the weighted least squares problem can be cast in complex variables and solved via the Gauss-Newton (GN) method. This paper presents a Perturbed Gauss-Newton (PGN) method in complex variables that is suitable for real-time tracking of the network's state vector. The proposed PGN method is built around an entirely linear measurement model expressed in function of the complex phasor voltages, and its iterative solution scheme requires one factorization of the coefficient matrix followed by repeated forward/backward substitutions. The complex variable PGN method for state estimation can be therefore seen as the counterpart of the classical implicit bus impedance method for power flow. The paper reports numerical results of the PGN method on large-scale transmission networks having up to 9241 nodes and contrasts the proposed method with the equality constrained GN method in complex variables and a recent two-stage estimator also operating in the complex domain. [ABSTRACT FROM AUTHOR]

This paper presents a new linear eddy current speed sensor with rectangular-shaped coils. The excitation coil and the pick-up coil have a perpendicular configuration without a magnetic yoke. The proposed sensor is shorter than the previous designs. The sensor works for a conductive moving target; in this paper we present calculations and an experimental verification for solid iron and aluminum moving part materials. A novel 3D analytical method is presented for the description and for the design of an eddy current speed sensor that is fast and has high precision. The source fields and the reaction fields caused by induced eddy currents are separated in our 3D analytical method, which facilitates an enhanced investigation of the features of the speed sensor. Evaluations of the effects of the moving part material and of coil lift off on the performance of the speed sensor are made with the use of a 3D analytical method. Measurements are performed for an eddy current speed sensor at different speeds up to 11.65 m/s and at different frequencies with a novel analytical model in terms of the induced voltage in the pickup coil versus speed. Simplicity and high precision are the main advantages of the proposed speed sensor. The achieved linearity error is 0.47% (measured) up to 11.6 m/s, and 0.43% (calculated) up to 117 m/s (420 km/h). [ABSTRACT FROM AUTHOR]

The paper proposes a technique for the on-line estimation of Thévenin equivalent (TE) which only needs the present phasor measurements. The technique is based on the wide-area measurements including voltage and current phasors of the system loads and synchronous generators, so that it can simultaneously estimate TE of the system seen from the interested buses. The technique has two main steps. In the first step, the conventional impedance matrix $\bar{Z}_{\rm bus}$ is modified to be suitable for TE estimation. In the second step, a correction coefficient based on the sensitivity theory calculated by using two consecutive phasor measurements is applied to correct the diagonal terms of the $\bar{Z}_{\rm bus}$ matrix. Simulation results carried on the IEEE 39-bus and 118-bus test systems show that the proposed technique can accurately estimate the TE for both generation and consumption buses under any load-increase scenario. The comparison scenarios verify the superiority of the proposed technique over others. [ABSTRACT FROM AUTHOR]

Penetration of DC networks is rapidly increasing in modern power systems. As transient behavior of DC grids is different from that of AC ones, AC grid protection schemes might not be applicable to protect DC networks. Exact fault location is vital for protection of DC networks to reduce repair cost and achieve fast power recovery. This paper proposes a novel topology independent multi-terminal DC scheme to identify fault section and location for DC transmission systems. Voltage and current signals measured at the terminals are analyzed by the least squares error (LSE) algorithm. Then, the proposed scheme uses low frequency components of the signals to locate DC faults offline. Unlike some other methods, it does not require sophisticated sensors and hardware to capture very high frequency content of the signals. Hence, the proposed scheme can be implemented in practice without additional measuring infrastructure. The performance of the proposed scheme is evaluated under various fault conditions for different topologies of DC networks in both overhead lines and cables. Numerous simulations carried out demonstrate that the proposed scheme is quite accurate and provides excellent performance under different fault resistances, sections, and locations. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental registrations and numerical simulations of the transient overvoltages caused by single phase intermittent arc earth fault in 35 kV network with isolated neutral. Experimental laboratory investigation is performed in order to implement appropriate arc fault model for arcs with low and discontinuous current. Single phase to earth arc fault is created in field in 35 kV network. Numerical model of the system is created in EMTP-ATP software. Overvoltage waveshapes and overvoltage factors are calculated and compared to measured values. Good agreement between the measured and calculated results is achieved. [ABSTRACT FROM AUTHOR]

This paper presents an intensive research on a multi-degree-of-freedom (DOF) motor and a new mechanism for power conversion based on continuous developments pursued since 2000. In fact, various structures have been proposed to operate more than two DOFs from one point of action, and their control methods have been thoroughly studied. As a result, the interpretations of both multiple DOFs to drive the motor and the operating characteristics have been considerably improved, but few applications of the motor have been developed. Practically and widely studied applications for this type of motor can include unmanned aerial vehicles, such as multi-copters and drones, whose operation can be enhanced by using multi-DOF motors. This paper details the investigation of the generic technology underlying these motors and a novel hybrid multi-DOF motor with improved tilting torque, practicality, and control for applications requiring actuation on more than two DOFs. Specifically, we present the electromagnetic separation of the rotation and tilt drives to simplify manufacturability and control. In addition, we describe the characteristics of various tilt actuators to increase the tilt torque. We designed, fabricated, and tested the proposed hybrid multi-DOF motor to verify its performance, and projected its application in a multi-copter. [ABSTRACT FROM AUTHOR]

The fault resistance and infeeded currents from tapped transmission lines are the two main challenges to establish correct fault location estimation in multi-terminal transmission lines. Also, fault location estimation in double-circuit lines is more complicated than single-circuit lines due to the effect of mutual coupling and inter-circuit faults. This paper proposes a negative-sequence network-based method to estimate the fault location of double-circuit multi-terminal transmission lines. In the presented method, signals are measured in the relay location and then, communication links are not required as it uses only one end measurements. Also, in conventional distance relays, six elements are needed to calculate the fault location in all types of faults. Furthermore, in this method, by using only one element for each transmission line, accurate fault location can be estimated. Also, high fault resistance, mutual coupling, and infeeded currents from tapped transmission lines do not have impact on the performance of the presented scheme. To investigate the effects of the line shunt capacitances on the proposed method, a PI model of the transmission lines is used in all the investigations. Simulation results carried out using MATLAB software indicate that the proposed scheme is able to produce excellent performance for the fault location estimation. [ABSTRACT FROM AUTHOR]