Initial Potential Distribution Research Articles

The Simulation Analysis on the Transient Process of Transformer

Power transformer is one of the important equipment in the power grid, we must ensure its reliable operation. To achieve that goal, the insulation property of power transformer must be fine, for its breakdown mainly caused by the insulation damage. When the power transformer suffered from the lightning surges, the windings insulation is damaged easily, so we should optimize and design on the power transformers windings insulation structure. Firstly, the computational methods of the inductance, capacitance and the resistance parameter were introduced in this paper, then the inductance, capacitance and the resistance parameters of a SFP-180000/220 three-phase transformer were calculated. Based on the equivalent circuit of transformer, the circuit model in the Matlab was established and simulated when the neutral is grounded or insulated respectively. The relevant initial potential distribution, the oscillating potential distribution, and the final potential distribution were gotten by the simulation. Finally, the characteristics of each potential distribution were analysed, which could provide some references to the insulation structure design for transformers.

Analysis on Overvoltage Relaxation of Lithium Secondary Batteries after Current Interruption

Introduction It is well known that the lithium ion secondary battery (LiSB) is the most promising power source for electric vehicle (EV), the further development is still needed to assure the life and performance prediction. To elucidate this, recent researches are focused on electrochemical impedance spectroscopy (EIS) method. However, these researches were mainly focused on to obtain data itself and resistance component of EIS by using parameter fitting technique with applying constant phase element without any further analysis on reaction kinetics. Especially the attribution of EIS spectra seemed to be miss-understanding since the theoretical consideration and modeling is not enough due to the complicated porous structure of electrode. There is another technique called as current-rest method1) suggested by Yata et.al. to obtain the internal resistance of LiSB. This technique is based on the measurement of over-potential relaxation after current interruption during the constant current charging/discharging process. However, the theoretical function of potential relaxation process with time is still not derived. In this paper, we derived the theoretical functions for the current rest method by applying the transmission line model. Results and Discussions The electrolyte solution generally used for LiSB is the 1:1 type electrolyte solution without the supporting electrolyte. In such a case, mass transfer by diffusion only should not be applied; we should take into account the migration with the diffusion at the same time. The ion flux can be expressed by the Nernst-Planck Equation. The effect of the convection is unclear up to now, the combination of diffusion and migration should be taken into account. Since the electro-neutrality should be fulfilled in the any part of the electrolyte solution, the familiar Fick’s law is still fulfilled by applying average diffusion coefficient. Thus, transmission line model can be applied for the mathematical derivation. The derivation of basic equation was carried out by using Laplace’s transform technique with the appropriate initial potential distribution and boundary conditions. In this paper, analysis have been made for the potential relaxation at separator so that the linear distribution was taken as the initial potential distribution. Thus obtained basic function had the series expansion form but it had the following feature. i) Initial response showed linear response to the square root of the time. ii) Long time response can be expressed in single exponential function to the time. iii) Both of the above functions are smoothly connected at dimensionless time T=0.5256 within the 0.2 % accuracy. Thus derived function was applied to the analysis of the measured voltage relaxation of commercially available LiSB for cellular phone. The voltage relaxation curves were well fitted by derived function. We employed the solver add-in of the Microsoft Excel in the parameter fitting process, where the time constant and the voltage difference was the fitting parameter for single time-constant function. For the case of fresh batteries with medium to high SOC level, showed two time constant system (50 s and 200 s) of which were connected in series. Fitted results were excellent within 1 mV deviation. On the other hand, the additional time constant system in the beginning of voltage relaxation were found for the SOC=0% and degraded battery. Even for such cases, the fitting of voltage relaxation were excellent by adopting three time constant system (0.3 s, 30 s and 250 s) of which were connected in series. We tested several type of LiSB such as cased in Al cans, 18650 type, and Al-laminated package, and the obtained results were almost similar. We concluded that the performance degradation of LiSB would appear in the beginning of the voltage relaxation with the order of magnitude of 0.1 s. As a conclusion, voltage relaxation measurement after current interruption was the powerful tool to obtain the information of the performance loss of LiSB. This technique may be the best choice for performance monitoring since the measuring time is short and the combination of charging/discharging is quite easy. References 1) S. Yata, H. Satake, M. Kuriyama, T. Endo, and H. Kinoshita, Evaluation of Positive Electrode Resistance by Current-Rest Method Using Four -electrode Cell, Electrochemistry, 78(5), 400-402 (2010)

Application of EIS and SKP methods for the study of the zinc/polymer interface

Electrochemical impedance spectroscopy (EIS) and Scanning Kelvin probe (SKP) were applied to study the zinc/polymer interface. The coating capacitance and the drop of potential across the zinc/epoxy interface are investigated as a function of water penetration and hydrolysis of adhesion bonds. Water penetrates to the interface, decreasing thus the potential drop and increasing the capacitance. Further removal of water leads to the restoration of bonds accompanied by a decrease in capacitance and the return to the initial potential distribution across the interface. Commercial high-performance coil coatings applied to galvanized steel were studied in order to correlate the interface stability and the tendency to blistering. EIS and SKP measurements allowed the evaluation of the electrochemical conditions at the interface. Local adhesion failures caused non-uniformity in the potential profile measured by SKP. Monitoring of changes in impedance at low frequency related to the interface during temperature cycling may be useful for the evaluation of the tendency to blistering.

Monte Carlo calculation of neck charging in cathode-ray tubes

The charging of the (insulating) neck glass in cathode-ray tubes (CRT) has been studied with the aid of Monte Carlo calculations. The charging of the inside neck glass is due to primary electrons generated by field emission from electrodes of the electron gun or backscattered from the screen, and to electrons generated by secondary emission processes. The simulations show that the wall potential distribution becomes stationary when the average secondary electron yield per incoming electron is equal to one at all wall positions. The electrons landing on the insulator are then transported along the insulator surface via small hops toward a metallized surface, where they are absorbed. Depending on the initial potential distribution and on the material properties, the wall may charge either positively or negatively, which leads to the convergence drift of the electron beams sometimes observed in CRT's.

Three-dimensional modelling of galvanomagnetic effects in lateral magnetotransistor structure

Abstract To optimize a lateral magnetotransistor (LMT) it is essential to know the initial potential distribution in the device, created by the majority carrier current. The potential distribution in an LMT structure is calculated by solving the Laplace equation in three dimensions (3-D). The obtained results are compared with those for 2-D modelling. It is shown that for a device whose length is greater than its width the 2-D model gives only a qualitative description.

Computerized potential distribution mapping: A new intraoperative mapping technique for ventricular tachycardia surgery

This study evaluated potential distribution mapping as a method for localizing the site of origin of ventricular tachycardia (VT). In contrast to conventional activation time maps, potential distribution maps require less editing and thus can be more automated and rapidly processed for interpretation of multiple beats of VT. As a series of potential distribution maps during VT is required for detailed analysis, an on-line computerized system was designed to display potential distribution maps sequentially at 1-ms intervals as a color movie. Potential distribution maps and activation time maps were constructed from 182 epicardial and endocardial unipolar electrodes during 12 episodes of reproducible monomorphic VT in 9 dogs four to six days after experimental myocardial infarction (mean cycle length, 162 ± 21 ms). At the onset of each depolarization during VT, a potential minimum abruptly developed on the surviving epicardium and another on the surviving endocardium of the left ventricle, both immediately adjacent to the subendocardial infarct. These two minima on the initial potential distribution maps corresponded to the sites of earliest epicardial and endocardial activation break-through recorded on the activation time maps. These two minima subsequently expanded or moved into the adjacent area and coincided with the spread of activation fronts on the epicardial and endocardial surfaces. Thus, the rapid display of sequential, computerized potential distribution maps of multiple beats of VT provides a dynamic means of identifying the site of origin of VT, and therefore should facilitate intraoperative mapping.

Some dynamical properties of very strong double layers in a triple plasma device

We present experimental results on three dynamic properties of very strong double layers observed in a triple plasma device. First, it is observed that when an inductance of sufficient size is inserted in series with the external bias supply used to produce the double layer, disruptions in the plasma current occur accompanied by disruptions in the double layer potential. Second, it is observed that with all external reactances reduced as much as possible, a sort of jitter-motion occurs in the position of the double layer around its equilibrium position. Third, when the external bias supply is pulsed, the initial potential distribution is observed to have an essentially uniform slope, as in the case of a vacuum capacitor. The disruption phenomenon may be explained in terms of the behavior of the potential structure as a function of the bias voltage and this explanation is discussed along with the experimental evidence for its validity. A comparable understanding of the other two phenomena has not been achieved, but in both cases there are qualitative differences between the behavior reported here and what has been observed in Q-machines and these differences are discussed.

Determination of an initial mesh for computer simulation of H-abrupt devices

A computer procedure to determine the initial potential distribution in the vicinity of semiconductor junction structures, in particular hyperabrupt ones, is outlined. The procedure has the advantage of cutting down on computation time, especially if high applied voltages are considered.

Voltage response of distributed RC lines with a discontinuous initial potential distribution

Prior work by this author has shown how the voltage step response of an initially quiescent RC line can be concisely expressed in terms of a set of higher transcendental functions. For convenience, the latter were defined in termsof integrals of elliptic theta functions and are termed “diffusion functions”. These same diffusion functions are also found to be useful in expressing closed-form solutions for the voltage response of distributed RC lines with a non-quiescent and discontinuous initial potential distribution. Results herein provide functional expressions for this voltage response with either open-circuited or short-circuited terminations. A variety of solution plots show how the responses change for different positions of the discontinuity. Also, plots of the diffusion functions are supplied showing their behavior over one complete cycle and more information on their symmetry properties is provided than was included in the initial paper.

Determination of an initial mesh for computer simulation of semiconductor devices with nearly abrupt junctions

A computer procedure to determine the initial potential distribution in the vicinity of semiconductor junction structures is outlined. It is useful for either n+-n or p-n structures and has the advantage that the mesh spacing is generated in such a way that its use for modelling under nonequilibrium conditions satisfies the stability requirements outlined by Seidman and Choo.