Transient Potential Distribution Research Articles

Design of hairpin windings considering the transient potential distribution

With the increasing use of novel semiconductor technologies such as SiC and GaN in inverter-fed electrical machines, the switching losses of the power electronics can be reduced. However, this leads to steeper voltage gradients, resulting in a strongly nonlinear transient potential distribution along the winding of the electrical machine. As a result, the insulation system – especially the turn-to-turn insulation – is subjected to additional voltage stress. To carry out targeted dimensioning of the insulation system, it is necessary to calculate the transient potential distribution in advance. In the design of a hairpin winding, it is possible to influence the transient potential differences by employing a method called “shifting” within the winding scheme and thus to reduce the maximum potential differences that occur. On this basis, a targeted design of winding plans with hairpins can be achieved. Here, both the transient potential differences between the conductors within a slot of the stator core and the potential differences between the conductors of different phases in the end winding region of the machine are considered. Furthermore, the voltage differences between the conductors and the stator core are determined and compared for different variants. In this way, it is possible to reduce the amount of material used in the insulation system. Finally, an advantageous winding layout plan based on reduced potential differences is compared with a reference plan.

An EMTP Extension for Computing Earthing System Transient Step and Touch Voltages

This paper presents a novel technique for computing dangerous voltages due to lightning transients imposed on earthing system, which is based on the use of the well-known ATP-EMTP software package. Earth surface transient potential distributions, as well as step and touch voltages computations, are performed through extending the widely used EMTP software package with a new post-processor (computer program), developed especially for that purpose. The earthing grid is approximated by the circular cross-section conductors. In numerical model, conductors are subdivided into segments (1D finite elements) and Clark's model with distributed constant parameters is then applied. Leakage conductance of conductor segments is modeled in EMTP as an additional lumped parameter. Analytical expressions for distributed and lumped segment parameters are derived using the average potential method. Due to the limitations of the EMTP, EM coupling between segments is neglected. The earth model is limited to the homogenous earth. Soil ionization effect is not accounted for, but could be incorporated, through some modifications of algorithms. Lightning surge model used is based on the Heidler's model of current source.

Transient potential distribution on transformer winding considering the effect of core lamination stack

The potential distribution of windings under impulse voltage is very important for the design of transformer inter-turn insulation especially for large capacity transformers such as ultra-high voltage direct current (UHVDC) converter transformer. Quite a lot of equivalent circuit models for transformer winding have been proposed for the potential distribution calculation assuming that the influence of magnetic core is negligible at frequencies higher than 10 kHz. However, lightning impulse or VFTO waveforms usually contain abundant frequency components higher than 10 kHz. At above situations the magnetic core plays an important role during the transient procedure. To obtain a more comprehensive model and also to provide a more accurate potential distribution of transformer winding, in this paper, a wide frequency magnetic properties of silicon steel sheet were measured and the relationship between relative permeability of lamination stack and frequency is studied and implemented in the calculation of frequency-dependent parameters such as resistance, self- and mutual-inductances. Then the equivalent circuit model of UHVDC converter transformer is established considering the properties of core lamination stack. Coding the program in MATLAB to solve the matrix equation and the potential distribution properties are extracted from the calculation results under lightning situation. The inter-turn potential distribution is also analyzed and the results may provide more accurate information for transformer inter-turn insulation design.

Analysis of the influence of dynamic components of AC/DC system on transient voltage stability based on energy function method

With the interconnection of large power networks, transient voltage stability of AC/DC power systems has been paid more attention in recent years. To investigate main influence of generating facility, high-voltage direct current (HVDC) and motor load for transient voltage stability, from the perspective of the generalised branch potential energy, the new indexes, and analysis method is proposed here. First, an energy function for AC/DC system is constructed with major dynamic components, namely classical HVDC control systems and motors in third-order model. Accordingly, the influence effects of the above major dynamic elements are investigated based on indexes from the corresponding generalised branch potential energy. With the rule of change in transient potential energy distribution in the network and information in stability margins, an evaluating procedure is established. Here, the judgment of transient voltage stability employs a heuristic energy function method. Finally, simulation tests on three-machine system with a HVDC transmission line are conducted in PSAT package, and the obtained results demonstrate the feasibility and effectiveness of the proposed method.

An arbitrary Lagrangian–Eulerian model for modelling the time-dependent evolution of crevice corrosion

An arbitrary Lagrangian–Eulerian (ALE) model is proposed to model the time-dependent evolution of a crevice corrosion that can achieve the simulation of the transient potential distribution, the dynamic concentration profiles and the time-dependent geometry deformation for a corroding crevice. The time-dependent deformation of the crevice geometry, which is caused by metal dissolution and corrosion product precipitation, is implemented via the ALE method. The model reasonably predicted the dynamic pH distribution inside the crevice. It is also predicted that the deposition of corrosion product accelerates crevice corrosion. The current model would be helpful in elucidating the mechanism of crevice corrosion and other forms of related localised corrosion.

OS0802 非定常熱応力を制御するスマート多層複合円板の解析

This paper deals with an adaptable stress control problem in a multilayer composite disk consisting of a transversely isotropic structural layer onto which piezoelectric layers are bonded. The piezoelectric layer next to the structural layer serves as a sensor and the other piezoelectric layers serve as actuators. It is assumed that a transient electric potential distribution is measured on the sensor layer when an unknown transient heating temperature distribution acts on the structural layer. The inverse thermoelastic problem is analyzed by employing the potential function methods as well as the finite difference method, so that the unknown heating temperature is determined from a knowledge of the electric potential distribution induced on the sensor layer. The transient maximum thermal stress in the structural layer can be suppressed by applying appropriate transient voltages to electrodes arranged on each actuator layer. The applied voltages are determined by optimization in order to minimize the maximum thermal stress at arbitrary time.

Dynamic Multiscale Quantum Mechanics/Electromagnetics Simulation Method.

A newly developed hybrid quantum mechanics and electromagnetics (QM/EM) method [Yam et al. Phys. Chem. Chem. Phys.2011, 13, 14365] is generalized to simulate the real time dynamics. Instead of the electric and magnetic fields, the scalar and vector potentials are used to integrate Maxwell's equations in the time domain. The TDDFT-NEGF-EOM method [Zheng et al. Phys. Rev. B2007, 75, 195127] is employed to simulate the electronic dynamics in the quantum mechanical region. By allowing the penetration of a classical electromagnetic wave into the quantum mechanical region, the electromagnetic wave for the entire simulating region can be determined consistently by solving Maxwell's equations. The transient potential distributions and current density at the interface between quantum mechanical and classical regions are employed as the boundary conditions for the quantum mechanical and electromagnetic simulations, respectively. Charge distribution, current density, and potentials at different temporal steps and spatial scales are integrated seamlessly within a unified computational framework.

OS1718 スマート多層複合円板における非定常熱応力の制御

This paper discusses a control problem of a transient thermal stress in a smart multi-layer composite disk consisting of a transversely isotropic structural layer onto which piezoelectric layers of crystal 6mm are perfectly bonded. The first piezoelectric layer serves as a sensor and the other piezoelectric layers serve as an actuator. It is assumed that a number of electrodes are arranged concentrically on the upper surface of each actuator layer. When an unknown heating temperature distribution acts on the bottom surface of the composite disk, a transient electric potential distribution is considered to be measured on the upper surface of the sensor layer. The unknown heating temperature can be inferred from the measured electric potential. Then, voltages applied to all electrodes can be determined by optimization so that the maximum transient thermal stress in the structural layer is minimized subject to constrains on the stresses in the piezoelectric layers. Finally, numerical results are shown in a table.

OS2605 非軸対称加熱を受ける圧電複合円筒の非定常熱弾性逆問題(OS26-1 西谷弘信セッション1,OS-26 西谷弘信セッション)

This paper deals with an inverse asymmetric transient thermoelastic problem of a composite hollow cylinder consisting of an inner structural layer and an outer piezoelectric layer. It is assumed that an unknown transient heating temperature distribution acts on the inside surface of the hollow cylinder and an induced transient electric potential distribution is measured on the outside surface. This inverse thermoelastic problem is analyzed by employing the finite difference method with respect to a time variable and the unknown heating temperature is inferred from the measured electric potential distribution. The numerical results obtained for a composite hollow cylinder made with a stainless steel layer and a cadmium selenide layer are shown in a graphical form.

Dangerous Voltages due to Direct Lightning Strike into the Communication Tower

This paper presents a novel technique for computing dangerous voltages due to direct lightning strike into the communication tower and associated earthing system, which is based on the use of the well-known ATP-EMTP software package. The earthing grid and the communication tower structure are approximated by the circular cross section conductors. In numerical model, conductors are subdivided into segments (1D finite elements) and Clark's model with distributed constant parameters is then applied. Because of the limitations of ATP-EMTP software package, the leakage resistance of buried segments is modelled as additional lumped parameter. Analytical expressions for distributed and lumped segment parameters are derived using the average potential method. Mutual electromagnetic coupling between segments is neglected due to the limitations imposed by the ATP-EMTP software package, which is based on transmission line approach. Separate computer program is developed for obtaining the earth surface transient potential distribution, from which step and touch voltages are then computed.

Systematic Study of Surface Chemistry and Comprehensive Two-Dimensional Tertiary Current Distribution Model for Copper Electrochemical Deposition

We present a two-dimensional, transient, tertiary current-distribution model for copper electrochemical deposition, with detailed surface chemistry kinetics for the model system of copper deposition with three representative additives; polyethylene glycol, bis-(sodium sulfopropyl) disulfide, and hydrogen chloride. Values of kinetic parameters are extracted from statistically designed rotating-disk-electrode experiments using a transport-reaction model of the experimental system. The resulting surface chemistry description is combined with fundamental conservation laws, including transient mass transport, momentum transport, and potential distribution, to form the tertiary current distribution model. Two-dimensional finite element simulations of this model provide new insight into causes of film thickness variations across the wafer, including large potential variations originating from the initial seed-layer thickness (terminal effect), a nonuniform mass-transport boundary-layer thickness resulting from cell geometry, and fluctuations in the additive concentrations. An application of pulse plating is also explored. The surface chemistry and the tertiary current distribution models could potentially form useful tools for design and optimization of copper electrochemical deposition processes.

Propagation characteristics of a positive surface streamer

AbstractThe potential distribution of a developing positive surface streamer was measured by the Pockels effect. The transient potential distribution along a linear path was measured at minimum resolutions of 20 µm and 2 ns. Additionally, velocity of a streamer, average electric field along a streamer, and the developing length were measured while changing the insulator thickness from 0.8 to 5.0 mm. The potential along a positive surface streamer decreases linearly with the distance from the high‐potential electrode, and its gradient is about 500–650 V/mm, which is independent of the inception voltage and the insulator thickness. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

An efficient technique for the evaluation of lightning-induced voltage in a cylindrical vessel containing charged oil

This paper proposes a numerical procedure, based on a mixed circuit-field approach to compute the transient and spatial potential distributions inside vessels containing flammable liquids, induced by a direct lightning strike. The circuit model is used to simulate the metallic vessel as an equivalent electrical network, which is solved by the SPICE simulator. In this way, it is possible to compute the transient potential distribution on the external vessel walls. These potential values are the boundary conditions of the partial differential equation system, valid at the inner of the container, which is solved by the finite-difference time-domain method. The model takes into account the transient and nonuniform volume charge density inside the liquid and the temporal accumulation of charges at the air/liquid interface. A validation of the proposed method, in the absence of liquid, is furnished. The transient and spatial distributions of the potential in the container are analyzed in order to detect possible hazards.

Potential Distribution Measurement of Surface Discharge Developing on Insulating Material

A new method for measuring the transient potential distribution of surface discharge is developed. The measuring system consists of a BGO Pockels crystal, an Ar ion laser, a beam expander, a streak camera and a CCD camera. The potential profile of a surface discharge along a linear path of 50 mm in length is measured with high space and time resolution: 0.1 mm and 2 ns in minimum resolution. Electric field near the tip of a stepwise negative surface discharge is around 24 kV/cm. When the stepwise surface streamer stops its propagation, the potential distribution around the tip of it forms similar profile regardless of the order of occurrence.

Noncontact measurement of transient potential distribution in superconducting cable

To measure transient potential distribution in a superconducting wire or cable after quench, some voltage taps are usually soldered with the sample conductor. However, the thermal and electromagnetic environment in the sample may be disturbed by the soldering of the voltage taps. As a method which can solve such problems, a noncontact measurement system with capacitance dividers is devised. It is experimentally found that our proposed method enables us to detect the quench initiation point and measure the propagation velocity of normal zone without any disturbances.

Potential distribution measurement of surface discharge by Pockels sensing technique

A new technique for measuring the transient potential distribution of electrical discharge is proposed. The measuring system consists of a Bi4Ge3O12 Pockels crystal, an Ar ion laser, a beam expander, a streak camera and a charge-coupled device camera. The potential profile of the discharge along a linear path of 50 mm in length is measured in the range of 0∼±36 kV. The temporal and spatial resolutions of this system are estimated to reach 2 ns and 0.1 mm, respectively. The potential distribution of a surface discharge creeping on a dielectric material is measured to clarify its developing mechanism. The tip of the propagating surface discharge has a high potential close to an applied potential. The maximum value of electric fields of a negative surface streamer exceeds 16 kV/cm in the direction of the streamer propagation.

Transient analysis of lossy transmission lines with arbitrary initial potential and current distributions

The method of characteristics has been generalized for the transient analysis of lossy transmission lines with arbitrary initial conditions. It is shown that traveling waves generated by the initial potential and current distributions can be simulated by voltage and current generators connecting to the terminals of the lossy transmission-line model consisting of ideal delay-lines and waveshaping networks synthesized by the modified Pade approximation. The discrete-time transient simulation requires neither the FFT nor convolution integral and is as efficient as the iterative waveform relaxation technique. Transient responses of lossy transmission lines with steady-state and transient initial potential and current distributions are simulated for illustration.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electromagnetic Transients in a Line-Transformer Cascade by a Numerical Laplace Transform Technique

The purpose of this work is to present a method for studying electromagnetic transients appearing in a power network consisting of a long transmission line and a transformer connected in cascade. An exact equivalent circuit representation of the system is developed using distributed element analysis in the s-domain. The proposed model assumes distributed inductances and self and mutual capacitances within the transformer windings. In addition, the new model can easily account for various connections of the transformer neutral. The line, which can be of any length, is represented by a single exact two-port network which is derived from distributed parameter theory. The new model yields closed form expressions in the s-domain for the transient potential distributions along the turns of the transformer winding as well as the connecting transmission line.

TOWARD UNDERSTANDING SOIL WATER UPTAKE BY PLANT ROOTS

We examine plant water uptake from a uniformly rooted soil volume by numerically solving the nonlinear diffusion equation for a soil cylinder bounded externally by an insulating surface, located at the half-distance between adjacent roots and internally by the root surface. A sinusoidally varying uptake rate is employed to simulate the diurnal evaporative demand, while the actual water flux across the inner surface is controlled by the root surface matric potential through a stomatal adjustment function. The analysis is conducted for Chino clay, Pachappa sand, and Indio silt loam, using hydraulic parameters determined from piecewise continuous exponential functions of the dependent variable matching data for these soils. The analysis uses root radii of 0.003, 0.005, 0.010, and 0.020 cm and root densities of 0.080, 0.142, 0.318, and 0.650 cm root length per cubic centimeter of soil. Results show that the transient matric potential distribution in the soil depends strongly on the precise nature of the hydraulic prameters for each soil: as the soil loses water by transpiration, the value of the bulk soil matric potential decreases monotonically at a rate dependent upon the specific water capacity of the soil. For initial bulk soil potentials of −0.3 bar in the Chino and Indio, and −0.2 bar in the Pachappa, the initial rate of potential decrease with time is greatest in the Chino, followed by the Pachappa and Indio, respectively. The corresponding radial potential distribution around individual roots depends upon the instantaneous value of the soil water diffusivity, which decreases as the soil dries, creating steep potential gradients adjacent to the root, with the largest initial gradients occurring in the Chino clay, followed by equivalent gradients in the Pachappa sand and Indio silt loam. The relative rate of decrease in the bulk soil potential and the drawdown around a root for the three soils, however, changes with time as the soil dries. The drawdown around a root is reduced by increasing root densities, so that at low densities the root surface potential depends more closely upon the diffusivity, whereas at high densities the root surface potential depends more closely upon the specific water capacity. In addition, roots of smaller radii exhibit greater drawdown as the total root surface area decreases and the flux of water at the root surface increases. The simulation of root water uptake using piecewise continuous functional relationships for the diffusivity and specific capacity produces results that form a coherent illustration of plant survival in three diverse soil environments.

Separation by Electrosorption of Organic Compounds in a Flow‐Through Porous Electrode: II . Experimental Validation of Model

The use of potential‐dependent adsorption to separate an organic compound from solution was demonstrated experimentally. Isotherms for the adsorption of β‐naphthol on glassy carbon were obtained over a range of potential of 1.0V. Adsorption of β‐naphthol, in dilute concentration, from aqueous electrolytic solution was also carried out in a flow‐through porous electrode consisting of nonporous microspheres of glassy carbon. A counterelectrode was located downstream and the potential was controlled at the end of the porous electrode nearest to the counterelectrode. Analysis of measurements of the transient potential distribution along the length of the porous electrode and of the current showed that each arose from charging of the electrical double layer. Profiles of effluent adsorbate concentration during both adsorption and desorption confirmed a theoretical model of electrosorption in a flow‐through porous electrode. Cyclic electrosorption was experimentally demonstrated.