90,479 research outputs found
A Prony-Based Approach for Accelerating the Lightning Electromagnetic Fields Computation: Effect of the Soil Finite Conductivity
No full textThis work provides an approach for speeding up the evaluation of lightning ElectroMagnetic (EM) fields in the case of a finite soil conductivity. The soil conductivity is taken into account through the well-known Cooray-Rubinstein (CR) approximation, which corrects the radial term of the electric field. A comparative analysis with some of the existing methods reveals an excellent accuracy with a substantial improvement in the CPU performance.SCI-STI-F
Field-to-Transmission Line Coupling Models With Special Attention to the Cooray–Rubinstein Approximation
No full textThere are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal–Price–Gurbaxani model, the Taylor–Satterwhite–Harrison model, and the Rachidi model. The Cooray–Rubinstein approximation is a procedure used by scientists and engineers to estimate the horizontal electric field from the lightning that is used in the induced voltage calculations for lines located over a finitely conducting ground. The Cooray–Rubinstein approximation is usually incorporated in calculating the induced overvoltages using the Agrawal–Price–Gurbaxani model. In this article, it is shown how this approximation could be incorporated into the other two coupling models. The resulting coupling equations are compared to each other by calculating the voltages induced on two idealized overhead transmission lines.SCI-STI-F
Analytical expressions for lightning electromagnetic fields with arbitrary channel-base current-Part I: Theory
No full textThe article provides analytical expressions for the electromagnetic fields generated by a lightning return stroke characterized by a channel-base current with arbitrary time waveform, in presence of either a perfectly conducting or a lossy ground, assuming the transmission line model for the current along the channel. In this second case, a time-domain analytical expression for the Cooray-Rubinstein formula is presented. The main idea that leads to the derivation of analytical formulas consists of dividing the channel into intervals in which the distance between the field source point and the observation point can be approximated with a linear function of the time, and of the spatial coordinates of both points. In the companion aticle, a detailed comparison is proposed with the classical (numerical) approach highlighting an excellent agreement both at close and far distances, considering all the values of practical interest for the ground conductivity. Moreover, the method guarantees a meaningful improvement in computational performance
The Grin of Schrödinger's Cat; Quantum Photography and the limits of Representation
No full textThe famous quantum physics experiment 'Schrödinger's cat' suggests that some situations are undecidable, i.e. they exist outside of the normative distinctions between 'truth' and 'false' because both states can co-exist under certain conditions. This paper suggests that photography has very close links with this state of affairs, because photography allows one to move from the world of certainty into the quantum dimension of undecidability and indeterminate states
Telegrapher's equations for field-to-transmission line interaction
No full textIn this chapter, we discuss the transmission line theory and its application to the problem of external electromagnetic field coupling to transmission lines, with particular reference to lightning-induced overvoltages on overhead power lines. After a short discussion on the underlying assumptions of the transmission line theory, we provide the derivation of field-to-transmission line coupling equations for the case of a single-wire line above a perfectly conducting ground. We also describe three seemingly different but completely equivalent approaches that have been proposed in the literature to describe the coupling of electromagnetic fields to transmission lines. The derived equations are extended to deal with the presence of losses and multiple conductors. The time-domain representation of the field-to-transmission line coupling equations, which allows for a straightforward treatment of non-linear phenomena as well as the variation in the line topology, is also described. Solution methods in the time domain are presented. The description of the main modelling features of an advanced computer code for the calculation of lightning originated voltages, i.e., the LIOV-EMTP-RV code, is given. The application of the illustrated theory and relevant computer codes to the case of a typical medium-voltage multi-conductor distribution feeder, which includes transformers and surge protection devices, is presented. The lightning performance assessment of traditional and compact overhead lines is dealt with as well
Melody in F [music] /
No full textCover title.; "The junior violin student".; "Celebrated melodies in 1st & 3rd positions for violin and piano ; 2nd violin part ad lib / edited & arranged by Cyril Monk.; MUS: N, MUSM 131113/28.; Also available online http://nla.gov.au/nla.mus-vn1519997; MUS: N, MUSM 131113/28
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