Surface wave, skin effect, and per unit length parameters of the single-wire transmission line at low frequency, for nonmagnetic and magnetic wires

Surface wave technology for high-speed communications is a current research topic aimed to respond to increasing data rate demands on existing copper infrastructures. Also, the topic of surface waves has recently gained importance in the modeling of transmission line towers hit by lightning strikes with spectral content in the megahertz band. The single-wire transmission line structure (return conductor absent) cannot support TEM waves; it supports a TM Sommerfeld wave fully described by two propagation constants and two characteristic impedances. Nonetheless, the literature on single-wire transmission-line structures has been employing quasi-static per unit length constitutive parameters, inductance and capacitance, borrowed from ordinary two-conductor transmission line TEM analysis. This work develops, discusses, and compares various possible definitions of these constitutive parameters using different physical approaches: TEM-approach, circuit-approach, and energy-approach. Numerical results for nonmagnetic and magnetic wires, copper and steel wires, respectively, are obtained in the range 1 Hz to 1 GHz. Our analysis shows that in some circumstances the TEM and circuit approaches may lead to nonphysical results, but, remarkably, all the approaches seem to converge to a common dominant term either in the per unit length capacitance or in the per unit length inductance, whose product is frequency-invariant. Considering the different approaches under discussion, the differences among the observed results for the per unit length constitutive parameters are negligibly small, of second-order importance

Flash boiling effect on swirled injector spray angle

Abstract A swirled injector for gasoline direct injection was used to investigate the effect of fuel flash boiling on the initial angle of the spray. The hollow cone spray was injected into a constant pressure bomb filled with quiescent air. The fuel was fed at 7 MPa constant pressure to the injector. Three parameters were changed to study the effect of the injection conditions on the spray angle: fuel composition, fuel temperature and air pressure in the test bomb. The injector tip was heated up to 150°C to keep the fuel to be injected at the desired temperature. Different blends of iso-octane and n-pentane were used to obtain fuels with different bubble temperature at the same air pressure. In a reduced set of experiments, only with pure fuels, the ambient pressure was varied to change the bubble temperature independently from the fuel temperature. It was observed that, when the fuel conditions exceed the bubble point, the spray angle, measured close to the injector, becomes wider. This angle was chosen as an indicator of the flash boiling intensity. The experimental results show that the angle value is well fitted by a unique correlation if it is expressed as a function of the ratio P=Pb/ Pair between the fuel bubble pressure and the bomb pressur

Ultrasubwavelength ferroelectric leaky wave antenna in a planar substrate-superstrate configuration

The possibility of achieving directive fan-beam radiation with planar Fabry-Pérot cavity antennas constituted by an upper ferroelectric thin film and a lower ground plane having ultrasubwavelength thickness is studied by means of a simple transverse-equivalent-network approach and a cylindrical leakywave analysis, deriving simple design formulas. The performance of the proposed antenna is investigated in terms of power density radiated at broadside and directivity in the principal planes, pointing out the main limitations and tradeoffs associated with the reduced thickness

Tower models for power systems transients. A Review

Fast-front transients play an important role in the insulation design of any power system. When a stroke hits the shield wire or the tower of high-voltage overhead power lines, flashover may occur either along the span or across tower insulators, depending on the relevant voltages and insulation strength. As a result, backflashover may take place from the tower structure to the phase conductor whenever a huge impulse current flows along the tower towards considerably high footing impedances. For these reasons, tower modeling for transients studies is an important step in the insulation design, and also for lower voltage applications, where indirect lightning effects may play a predominant role. However, after decades of research on tower modeling, starting from the 1930s with the first model proposed by Jordan, no consensus has been reached neither on a widely accepted tower model nor on the quantitative effect of the tower models on insulation design. Moreover, the fundamental mechanisms at the base of the transient response of towers and the definition of some fundamental parameters have not been totally clarified yet. The aim of this review is to present the available tower models developed through the years in the power community, focussing mainly on lumped/distributed circuit models, and to help the reader to obtain a deeper understanding of them

Setting up a PDPA system for measurements in a Diesel spray

Abstract. A PDPA system was set up, optimised and used to measure the time resolved characteristics of the droplets inside a spray produced by a common-rail diesel fuel injection system. Some preliminary tests are performed with gas flows to optimise the optical set-up. Parametric studies are performed to gain an understanding of the particle density limits of the system, and their dependence on PDPA system parameters. Then the diesel spray produced by a single-hole injector is measured, with the fuel pressure ranging from 500 to 1300 bar, gas density in the test chamber ranging from ambient conditions to 40 kg/m3. Fuel and gas temperature were 25ºC. Beam waist size is reduced to the minimum value allowed by the optical stand-off of the spray enclosure. Receiver lens focal length is similarly reduced. Receiver slit width, which is found to have a dramatic effect on the detection of droplets during the injection period, was tested in the range from 100um to 25um. Tests performed with two different slit heights are tested, respectively 1mm and 50 μm, show that this parameter has minimal effect on performance. PMT voltage (gain) is held to a moderately low value between 400 and 500 volt and the laser power between 400 and 800 mW in the green line. Optimum burst threshold is found to obtain the best quality data regardless of background level, which varies greatly in high-density pulsed sprays

Modeling of conductors catenary in power lines: effects on the surge propagation due to direct and indirect lightning

In this article, the effects of the variable height in overhead power lines are investigated with reference to the surges produced by direct and indirect lightning events. Simulations are carried out both by an implicit finite-difference time-domain scheme and by the commercial tool EMTP-RV. Differences in the waveforms computed by the two approaches are discussed and clarified. Additionally, the validity of the commonly adopted assumption of weakly varying vertical component of the incident electric field is investigated

Efficient Modeling of Discontinuities and Dispersive Media in Printed Transmission Lines

The finite-difference time-domain method is applied to the analysis of transmission lines on printed circuit boards. The lossy, dispersive behavior of the dielectric substrate is accurately accounted for by means of several algorithms whose accuracy is discussed and compared. Numerical results are validated by comparisons with measurements and an equivalent circuit of slot in the ground plane is proposed

Differential Signalling in PCBs: Modeling and Validation of Dielectric Losses and Effects of Discontinuities

This paper focuses on differential signal transmission above ground planes with gaps, taking into account the dielectric and conductive losses of the substrate. An equivalent lumped-circuit is proposed and its suitability is investigated by comparing the obtained numerical results with the measured data. Furthermore the differential to common mode conversion of the waves, while crossing the gap, is theoretically analyzed and experimentally verified

Systematic review of energy theft practices and autonomous detection through artificial intelligence methods

Energy theft poses a significant challenge for all parties involved in energy distribution, and its detection is crucial for maintaining stable and financially sustainable energy grids. One potential solution for detecting energy theft is through the use of artificial intelligence (AI) methods. This systematic review article provides an overview of the various methods used by malicious users to steal energy, along with a discussion of the challenges associated with implementing a generalized AI solution for energy theft detection. In this work, we analyze the benefits and limitations of AI methods, including machine learning, deep learning, and neural networks, and relate them to the specific thefts also analyzing problems arising with data collection. The article proposes key aspects of generalized AI solutions for energy theft detection, such as the use of smart meters and the integration of AI algorithms with existing utility systems. Overall, we highlight the potential of AI methods to detect various types of energy theft and emphasize the need for further research to develop more effective and generalized detection systems, providing key aspects of possible generalized solutions

Ground-return parameters of submarine cables buried in the seabed

The computation of sea/seabed-return distributed parameters of subsea cables is a relevant topic due to the growing importance of submarine connections. This article presents for the first time new formulas for the computation of self and mutual ground impedances and admittances for submarine cables buried in the seabed. The original theory developed by Sunde is applied to a three-media model with air, sea, and seabed. Referring to the practical installation practice of the Italian transmission system operator Terna S.p.A., we compare the prediction of the available models and assess the effect of the different approximations on the computation of the per unit length ground parameters. Finally, we define the limits of applicability of the available models that differ in accuracy and complexity