Different modes of runaway electron beams generated in high-pressure gases

This article presents the results of experimental studies of different modes of a runaway electron beam (RAEB) generation in high-pressure gases as well as X-rays caused by it. In particular, the mode with the greatest beam current amplitude, the one with two current pulses, that with the X-ray pulse duration of 100s ns, the mode in which a RAEB propagates in the direction opposite from an anode, and some others are described. The effect of the cathode design and material on the RAEB current amplitude and duration in atmospheric-pressure air is shown. When analyzing the most common modes, the features of the gap breakdown are used.

The Assessment of a Magnetizing-Current Inrush of a Power Transformer

The study aims to propose an analytical tool for determining the parameters of the power transformer magnetizing inrush current caused by geomagnetically induced currents flowing through high-voltage windings with a grounded neutral under the impact of geomagnetic disturbances on the power grid. The analytical equations for the instantaneous magnetizing current under geomagnetic disturbances were obtain by mathematical model of magnetizing branch for a shell-type power transformer. A model base on a magnetization characteristics piecewise-linear approximation for the electrical steel. The magnetizing inrush current amplitude and duration it was found depends on the intensity of geomagnetic disturbances and in cope-link with the dynamics of the power transformer core saturation transient process were determined the changes in the magnetizing inrush current amplitude and duration under geomagnetic disturbances. The magnetizing inrush current amplitude it was found may reach the level of short-circuit current periodic component at the point of power transformer grid connection. The results were verify by comparing the design and experimental values of the magnetizing inrush current amplitude. The advantages of proposed mathematical model shown with justifying the analogy between core saturation under connecting of power transformer to a grid and under geomagnetically induced currents exposed. The piecewise-linear approximation of power transformer magnetization characteristic, allow to obtain the amplitude value of magnetizing inrush current caused by geomagnetically induced currents with an accuracy of 6% and can be used with power grid steady state and transient simulation under geomagnetic disturbances.

Electrodynamics of dual-band end-fed wire dipole radiators

This paper briefly describes an analysis of main electrodynamic characteristics required in design of dual-band Yagi antenna exciters consisting of two electrically thick conductors. The study of end-fed excitation of the said system of conductors allows to predetermine the design of conceptually new circuits of classic dipole radiators, avoiding closely-spaced arrangement of feeding strips that ensure direct excitation of dipole arms and, therefore, reducing their electromagnetic spurious coupling. The latter prevents asymmetry in surface current amplitude distribution on dipole arms and allows to improve its directivity and matching with a power feeder.

Statistical Analysis of Lightning Flashes over Wind Parks in Greece

Currently, lightning phenomenon, mechanisms, and impacts on lives and infrastructures have been satisfactorily decoded and studied. Sound knowledge of lightning parameters is available in international literature. Yet, there are few studies referring to lightning statistics such as the number of flashes over an area, current amplitude distribution, etc., except for official documentation from national weather services, perhaps because of the stochastic nature of lightning. This work presents full recorded data for lightning flashes over wind farms distributed at the Hellenic territory. The data come from real time measurements at wind farm stations from 2011 to 2020 and concern number of CG flashes and lightning current amplitude. They are statistically processed and analyzed and contain useful information regarding the lightning characteristics of various geographic regions all over the country. Furthermore, the study displays data from field measurements of ground resistance at wind turbines and highlights techniques of designing and enhancing grounding systems of wind turbines for given lightning protection level (LPL). The present study, therefore, provides stakeholders with useful data and noteworthy conclusions about lightning occurrence and characteristics in Greece in order to make informed decisions on the various project stages, such as selection of the wind farm site, proper and in-depth risk assessment, and investment in safety measures for personnel and equipment.

Modeling and Analysis of Lightning Protection in an Emergency Situation of a Lightning Strike

The grounding of the supports determines the resistive, the most significant component of the overvoltage acting on the insulation gap between the lightning rod and the equipment of the electrical substation when lightning strikes the lightning rod. (Research purpose) The research purpose is in developing recommendations for the grounding devices for lightning rod supports and means of suppressing sliding spark channels in a multi-wire system. (Materials and methods) The estimation of the share of lightning current in the grounding conductor of the lightning rod support can be calculated simplistically. This makes it possible to abandon the solution of long-line wave equations and switch to a substitution scheme with concentrated parameters, in which the active and inductive resistances of sections of an electric circuit loaded with lightning current should be considered, with mandatory consideration of inductive connections between them. (Results and discussion) The article presents the calculation for a pulse with an oblique front and a flat head, which is traditionally used to estimate the number of reverse overlaps on an overhead power transmission line when a lightning strike hit a support. It was assumed that the lightning strike occurred in the extreme thunderstorm, the current load mode of which is the least favorable. The greatest current load of the grounding conductor of the support corresponds to a direct lightning strike, when the current amplitude there differs from the current amplitude of the first component in the lightning channel by no more than 25 percent, this mode should be taken as the calculated one when estimating the maximum length of the sliding spark channel. (Conclusions) The maximum lengths of sliding spark channels in soils of different conductivity were determined using computer modeling of an emergency situation of a lightning strike, provided that the reinforced concrete foundations of the lightning rod supports connected by an underground horizontal bus are used as grounding conductors of lightning rods. The most effective means of limiting the danger of sliding spark channels is their forced orientation to the side, which is safe for the grounding circuit of an electric substation.

Long-term effects of moderate concussive brain injury during adolescence on synaptic and tonic GABA currents in dentate projection neurons.

Progressive physiological changes in the hippocampal dentate gyrus circuits following traumatic brain injury contribute to temporal evolution of neurological sequelae. Although early posttraumatic changes in dentate synaptic and extrasynaptic GABA currents have been reported, whether they evolve over time and remain distinct between the two projection neuron classes, granule cells and semilunar granule cells, has not been evaluated. We examined changes in tonic GABA currents and spontaneous inhibitory postsynaptic currents (sIPSCs) and in dentate projection neurons one and three month after moderate concussive fluid percussion injury (FPI) in adolescent rats. Granule cell tonic GABA current amplitude remained elevated up to one month after FPI, but decreased to levels comparable to age-matched controls by three months postinjury. Granule cell sIPSC frequency, which we previously reported to be increased one week after FPI, remained higher than in age-matched controls at one month and was significantly reduced three months after FPI. In contrast to the early decrease, tonic GABA current amplitude and sIPSC frequency in semilunar granule cell was not different from controls three months after FPI. The switch in granule cell inhibitory inputs from early increase to subsequent decrease could contribute to the delayed emergence of cognitive deficits and seizure susceptibility after brain injury.