Transient Field Distribution Research Articles

Influence of volume and surface conductivity on the transient surface charge characteristics of DC‐GIL insulator under thermal–electric coupled fields

Here, the transient surface charge distribution of a basin-type insulator is investigated under thermal–electric coupled fields. Horizontally installed ±200 kV direct current gas-insulated transmission lines (DC-GIL) are employed, and a 3D geometric model is applied. An improved method is introduced in the transient simulation under coupled fields, which involves simplifying geometric model, decoupling calculation, applying weak form partial differential equation, and simplifying ion transport equation. The influence of volume and surface electric conductivity on the transient surface charge and electric field distribution is discussed. With increasing volume conductivity, the transient charge accumulation is accelerated due to the promotion of conduction through the insulator. With increasing volume conductivity, the polarity of the charge on convex surface changes from negative to positive, while it changes from positive to negative with increasing surface conductivity. This is the consequence of the transition in dominant conduction mechanism. Non-monotonic variation of charge density is observed attributing to the variation transient field distribution. It can be concluded that the influence of volume and surface conductivity should be focused on when evaluating the insulation characteristics of DC-GIL insulators, and the thermal gradient should be considered in dealing with the long-term operating insulators.

Integrated Massively Parallel Simulation of Thermo-Electromagnetic Fields and Transients of Converter Transformer Interacting With MMC in Multi-Terminal DC Grid

A computationally efficient model to study the transient interaction of the finite-element (FE) converter transformer with modular multi-level converter (MMC) can provide the advanced knowledge of the filed-circuit interactions that can be utilized for the design and test of equipment; however, the runtime of existing simulation tools developed for CPU execution usually takes days or even weeks, which is prohibitively long. In this paper, an integrated thermo-electromagnetic model is proposed for the transient simulation of FE-based transformer interacting with the MMC in a multi-terminal dc gird, with the magnetic field, thermal field, and electrical networks fully coupled. The transmission-line modeling solution is employed for the nonlinear FE problem, and each MMC is split into a number of minimum possible circuits, so that the codes can be sufficiently parallelized and implemented on the graphics processing unit with thousands of Cuda cores to be runtime friendly. The integrated model can provide the transient field distributions within the transformer and the device-level information of the MMC such as switching transients and junction temperatures. Compared with a commercial software package, the execution time of $10^5$ time-steps decreased from several days to only hours with a speedup of more than 47 times while maintaining high accuracy.

Comparison of Electrostatic-Field and Transient-Field Distributions for Insulators in Pulsed Power Systems

The difference between transient-field distribution (TFD) and electrostatic-field distribution (EFD) is investigated by establishing models for a coaxial line with a supporting dielectric in it and a vacuum insulator with an equivalent load. By simulating the coaxial line model, it is found that the TFD is totally different from the EFD in that the maximum electric field strength ( $E_{\mathrm {max}}$ ) of the TFD is almost 2 times of the $E_{\mathrm {max}}$ of the EFD. It is considered that the wave reflection leads to the increase of $E_{\mathrm {max}}$ of the TFD. By simulating the vacuum insulator model, it is found that the TFD on the insulator surface is dependent on the impedance of the load ( $Z_{\mathrm {load}}$ ), whereas the EFD keeps constant as $Z_{\mathrm {load}}$ changes. Factors such as load impedance, gap between insulator and metal, pulsewidth, and pulse rise time are selected to further research the differences between the TFD and the EFD methods. It found that the load impedance and the gap between insulator and metal influence the TFD greatly, whereas the pulsewidth and pulse rise time have less influence on the TFD. The difference of TFD and EFD can be used to calculate the impedance distribution of an insulator in practice.

Electric field control in DC cable test termination by nano silicone rubber composite

The electric field distributions in high voltage direct current cable termination are investigated with silicone rubber nanocomposite being the electric stress control insulator. The nanocomposite is composed of silicone rubber, nanoscale carbon black and graphitic carbon. The experimental results show that the physical parameters of the nanocomposite, such as thermal activation energy and nonlinearity-relevant coefficient, can be manipulated by varying the proportion of the nanoscale fillers. The numerical simulation shows that safe electric field distribution calls for certain parametric region of the thermal activation energy and nonlinearity-relevant coefficient. Outside the safe parametric region, local maximum of electric field strength around the stress cone appears in the termination insulator, enhancing the breakdown of the cable termination. In the presence of the temperature gradient, thermal activation energy and nonlinearity-relevant coefficient work as complementary factors to produce a reasonable electric field distribution. The field maximum in the termination insulator show complicate variation in the transient processes. The stationary field distribution favors the increase of the nonlinearity-relevant coefficient; for the transient field distribution in the process of negative lighting impulse, however, an optimized value of the nonlinearity-relevant coefficient is necessary to equalize the electric field in the termination.

Transient field distribution in gas-solid insulation systems under DC voltages

The development of electric fields in gas-solid insulation systems under dc voltage stress goes hand in hand with the accumulation and decay of charges on dielectric interfaces. The charge transport through the solid insulator and the gas is determined by the electric properties of the involved insulating materials. Therefore, the nonlinearly field-dependent volume conductivity of a gas, resulting from a constant charge generation rate by natural ionization has to be considered. The transient field distribution on insulators under dc voltage is investigated theoretically, using a gas model, which takes into account the physical characteristics of insulating gases like air and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> as well as the effects resulting from electron emission from the electrodes. The influence of the ion pair generation rate in the gas, the electric field strength, and the volume and surface conductivity of the solid insulating material on the development of the electric field is investigated on cylindrical and conical insulators which are typical for gas insulated systems. Results of calculations using the gas model are compared to simulations assuming constant gas conductivity. The simulation results are verified by measurements of the surface potential on cylindrical epoxy resin insulators in air.

Transient field distribution in gas-solid insulation systems under DC voltages

The development of electric fields in gas-solid insulation systems under dc voltage stress goes hand in hand with the accumulation and decay of charges on dielectric interfaces. The charge transport through the solid insulator and the gas is determined by the electric properties of the involved insulating materials. Therefore, the nonlinearly field-dependent volume conductivity of a gas, resulting from a constant charge generation rate by natural ionization has to be considered. The transient field distribution on insulators under dc voltage is investigated theoretically, using a gas model, which takes into account the physical characteristics of insulating gases like air and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> as well as the effects resulting from electron emission from the electrodes. The influence of the ion pair generation rate in the gas, the electric field strength, and the volume and surface conductivity of the solid insulating material on the development of the electric field is investigated on cylindrical and conical insulators which are typical for gas insulated systems. Results of calculations using the gas model are compared to simulations assuming constant gas conductivity. The simulation results are verified by measurements of the surface potential on cylindrical epoxy resin insulators in air.

Dynamics of coupled plasmon polariton wave packets excited at a subwavelength slit in optically thin metal films

We study by numerical simulations the excitation and propagation dynamics of coupled surface plasmon polariton (SPP) wave packets (WPs) in optically thin Ag films and a bulk Ag/vacuum interface under the illumination of a subwavelength slit by 400 nm continuous wave (cw) and femtosecond pulsed light. The generated surface fields include contributions from both SPPs and quasicylindrical waves, which dominate in different regimes. We explore aspects of the coupled SPP modes in Ag thin films, including symmetry, propagation, attenuation, and the variation of coupling with incident angle and film thickness. Simulations of the electromagnetic transients initiated with femtosecond pulses reveal new features of coupled SPP WP generation and propagation in thin Ag films. Our results show that, under pulsed excitation, the SPP modes in an Ag thin film break up into two distinct bound surface wave packets characterized by marked differences in symmetries, group velocities, attenuation lengths, and dispersion properties. The nanometer spatial and femtosecond temporal scale excitation and propagation dynamics of the coupled SPP WPs are revealed in detail by movies recording the evolution of their transient field distributions.

Focus on magnetics and electromagnetism

Focus on magnetics and electromagnetism

Transient Field Distribution in a Transformer Affected by Variably Loaded Secondaries

Abstract— Ring core transformers are analysed by using a two dimensional axisymmetric model. The primary and secondaries are foil windings surrounding a core with finite permeability. The secondaries are positioned between core and primary winding. They can either be short circuited or connected to a resistive or inductive load. The current in the primary is constant up to the switching point at t = 0. At this moment it is abruptly forced to zero hereby causing transient fields in all windings. The spatial distribution and temporal devolution of these fields is affected by the loading of the secondaries.

Simulation of unipolar space charge controlled electric fields

A model is discussed, which allows in an easy way to perform electric field simulations in unipolar space charge controlled dielectric media with the finite element method. The approach is appropriate for a variety of different devices in electrical engineering, containing solid, liquid, or gaseous insulators. The main issue concerns the boundary condition at the charge injecting contacts, including ohmic contacts (leading to space charge limited currents) as well as contacts with a finite threshold field for injection (e.g., by Corona onset in gas). The model naturally contains the high-current limit, where the current is injection dominated, i.e., given by the saturation current of the contact, and the capacitive field is restored. Results for a few examples are presented, in order to validate the method by comparison with analytical results, and in order to illustrate its usefulness for applications. In particular, for gaseous insulation various steady state and transient field distributions are calculated. With this approach it is easily possible to investigate the effect of convective currents as well as the charging of dielectrics surfaces.

Unified analysis of ridge‐waveguide slot antenna in three‐dimensional space and time

AbstractRecently, there has been much interest in research and development of a high‐power heating system for nuclear fusion plasma heating. Since these systems deal with high power, there are several problems that are different from those in the sources for communication systems. A structure is proposed which is based on the T‐type ridge waveguide, a simple and sturdy configuration. In these systems, the complex near field due to the three‐dimensional structure including the medium conditions has a significant effect on the characteristics. Especially, in a high‐power system, the effect of higher‐order modes with relatively small power distributions cannot be neglected. Also, transient field distributions strongly affect the characteristics so that the time domain response must be analyzed. This paper applies an analysis technique for the three‐dimensional space and time based on the Bergeron method to the systematic analysis of the radiated near field from the entire system of a T‐type ridge waveguide slot antenna including the waveguide, slot and the heating regions. The power distribution of the field determining the fundamental properties of the heating system is found in terms of the Poynting vector and the fundamental properties of the system are obtained. Specifically, the effect of the dielectric material on the field distribution is found. The cutoff characteristics of the ridge waveguide and the fundamental properties of the slot are studied and their characteristics are investigated.