The location of faults in low-attenuation coaxial cables and open-wire lines by the use of the echo-ranging techniques of radar prompted this investigation of a method to accurately locate faults in underground power cables. As the propagation-velocity of disturbances on a smooth line or cable is constant, the time delay between the transmission of a pulse into a cable and the reception of an echo from an internal discontinuity is proportional to the distance to the discontinuity. The low inductance and high dielectric losses in power cables attenuate and distort the pulses. This distortion limits the accuracy and range of equipment which must measure time intervals to the nearest 3 x 10⁻⁸ seconds. Basically, the Echo Ranger consists of a portable low-voltage impulse generator combined with a timing Oscillator and a delayed high-speed sweep on a commercial split-beam oscilloscope. A high-power hydrogen thyratron delivers 0.1-microsecond pulses of five kilowatts (peak) to the cable. Although the range of the apparatus now constructed is only two miles on power cable, faults at least five miles away should be visible. The minimum resistance of a detectable series fault is about five ohms and the maximum resistance of a detectable shunt fault is about 2000 ohms. Without modification, the Echo Ranger can be used on overhead lines up to four miles long. On a 1044-foot piece of RG8U polyethylene cable, two 100-ohm shunt faults 20.8 feet apart were located within 0.63%. On a three-conductor oil-filled lead-sheathed power cable 1389 feet long, a transformer tap 424 feet away and a Joint 320 feet away were located within 1.2%. The apparatus can be readily modified to deliver 16-kilovolt 5-megawatt (peak) pulses to initiate and locate an arc at incipient faults. The power to hold the arc must come from a superimposed power supply such as a kenotron set or the normal line voltage. Further refinements which increase the accuracy and range without sacrificing simplicity of operation could be applied to advantage. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The Location of a fault in a power cable is by no means a simple task and the techniques used at present warrant further improvement. Many methods of fault location have been devised but each has its particular limitations. Some of these methods include D.C. and A.C. bridge methods, echo-ranging methods, and high-frequency methods. The limitations and impracticability of these various techniques has been the main reason for this research. In this thesis, a review of the high-frequency method has been made, resulting in the development of a method of locating high-resistance faults. Expressions, permiting the use of this improved method in instances where cable potheads are relatively inaccessible have also been developed and checked experimentally. Briefly, the method consists of determining the input impedance of the cable with its remote end terminated in its surge impedance. This is done by simultaneously measuring the voltage drops across a standard resistor and across the cable. The ratio of these drops is an indication of the cable impedance at that frequency. Observations are taken on a band of frequencies on a faulted cable and on a good cable, both terminated in the characteristic impedance. The difference of these two effects is attributed to the reflections from the fault. From the plot of the impedance as a function of the frequency, by a short graphical computation, the distance to the fault may be obtained. Faults as high as twenty times the surge impedance have been successfully located on relatively short lengths of cable. The distance to the fault has been estimated well within [page missing] / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The wind-induced vibration of bridge stay cables has been a long studied and documented topic including a vast literature presenting experimental and numerical investigation results. There are several aerodynamic phenomena which can be associated with the wind-induced vibrations of bridge stay cables, such as vortex-induced vibration, rain-wind induced vibrations, buffeting phenomenon, dry cable galloping, and high-speed vortex excitation, to name a few. One of the most critical types of vibrations for slender structures exposed to wind is the galloping instability. This is typically not encountered for round structures, like circular cylinders or cables, due to their symmetrical nature, and therefore a lack of negative slope in the lift coefficient. However, vibrations of inclined cables of cable-stayed bridges have been noticed for several bridges, and were associated with partial damage of the cable stays, and damaged noted to cable anchors. It is still unclear if these cable vibrations are caused by dry inclined cable galloping, or by high speed vortex excitation. For this reason, stay cables construction guidelines (FHWA, 2005) have not been able to clearly identify the aerodynamic instability resulting in the recommended use of high structural damping, and high Scruton numbers used to limit bridge stay cable vibrations. The current research addresses these issues by performing numerical CFD (computational fluid dynamics) simulations of wind flow around inclined and yawed cables in order to identify the flow behaviour around the circumference and downstream of the cable. Such numerical models provide a new understanding regarding the flow conditions around an inclined cable and the beginning of dry galloping instability. The simulation was performed for full scale cables in the form of cylinder models with high aspect ratios. The arrangement for the cable was considered as a combination of the inclination and yaw angles, in such a way that it should match the experimental setting considered by Cheng et al (2003), based on which a validating comparison of results was performed. A LES (Large Eddy Simulation) model was developed with a constant Smagorinsky model for simulating the turbulent flow around the cylinders. Reynolds numbers (Re) ranging from 1.1 × 105 to 6.7 × 105 were investigated for various combinations of the inclination angles of 0° to 60° and yaw angles of 0° to 40°. The diameter of the circular cylinder was set to D = 0.089 m and the length of the cable was 2.67 m (30D). Pressure on the surface of the cylinder was monitored on 5 rings arranged along the circular cylinder at equal intervals and velocities were recorded for intervals of 0.1 – 0.5D downstream the cylinder. Also pressure, vorticity and streamlines distributions were recorded for several plans along and across the cylinder. The flow pattern visualisations were clearly established and wind speed profiles were presented. An axial flow along the leeward side of the cylinder was identified for inclined circular cylinders. The predominant axial flows were noted at intervals of 0.1D to 0.3D downstream of the cylinder. As the distance from the leeward side of the cylinder increased, the effect of the far field flow increased as well, for the flow around the leeward side of the cylinder. The drag crisis encountered as a sudden drop in the drag coefficient CD, with the increase of Re number, was confirmed. The preliminary results for inclined cylinders showed good agreement with the experimental results available in the literature. Slight discrepancies for the upper and lower branches of the drag crisis were found between the published data and results obtained in the current study. A new flow classification for inclined and/or yawed circular cylinders was proposed based on the velocity profiles, eddy viscosity, and swirl threads formations, as a combination of the TrSL and TrBL regimes similar with the ones defined by Zdravkovich (1997), for flow perpendicular to cylinders. Four cases showed a potential aerodynamic instability when results of the current study were employed into the theoretical aerodynamic damping equation derived by MacDonald and Larose (2006). Three of these cases demonstrated a similar flow phenomenon to the TrSL-Short flow phenomenon defined in this study, which occurs when the major axis of the ellipse is close to the direction of flow, and the turbulent shear layers detach almost on the leeward side of the cylinder. The coherence, cross-coherence and cross-bicoherence were calculated for the frequency components of the coefficient of lift, the pressure coefficient along the leeward side of the cylinder, and the total velocity along the leeward side of the cylinder, and it was found that three cases of low non-linear interaction, intermediate non-linear interaction, and high non-linear interaction could be identified. Also it was concluded that the interaction between the lift and pressure coefficients monitored for the cylinder and the variation of the total velocity component, did not have a significant influence on the flow regimes, or on the transition between the flow regimes. The high-nonlinear interactions relate more to the potential coupling between the frequencies of the parameters mentioned above, especially for the critical case of 60° relative angle.

The impedances of cables are some of the parameters needed for various studies in cable systems. In this work, the impedances of cables are calculated using the subdivisions of the conductors (including ground) in the system. Use is also made of analytically derived ground return formulae to speed up the calculations. The impedances of most linear materials are calculated with a good degree of accuracy but materials with highly nonlinear properties, like steel pipes, give large deviations in the results when they are represented by the linear model used. The method is used to study a test case of induced sheath currents in bonded sheaths and it gives very good results when compared with the measured values. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Unknown

No description available.

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed March 31, 2008) Includes bibliographical references (p. 48-49).

Ingeniero Civil Mecánico / Prodinsa es la única empresa en Chile dedicada a la fabricación de cables de acero. Generalmente, los cables utilizados en palas mineras y grúas de altas prestaciones, están sometidos a altas cargas de trabajo cíclico durante su vida útil. La reiteración de los esfuerzos de flexión, extensión y contacto que se originan en cables que operan en condiciones dinámicas genera fatiga, siendo éste su principal mecanismo de falla. La carga de trabajo y el tamaño de las poleas, son las condiciones operacionales más influyentes en la vida del cable. Así mismo, los parámetros de diseño del cable, como su diámetro y construcción, lo caracterizan y determinan su comportamiento. Para poder realizar buenas estimaciones sobre la vida útil de distintos tipos de cables que presten servicios dinámicos, se realizan ensayos de fatiga. Mediante este tipo de ensayos, es posible obtener valiosas conclusiones sobre cómo distintos factores influyen en el comportamiento de los cables, permitiendo así determinar qué construcciones son más aptas para cada aplicación y bajo qué condiciones de operación presentan un rendimiento óptimo. El objetivo del presente trabajo es diseñar una fatigadora de cables de acero que cumpla con estándares internacionales y que satisfaga las necesidades de Prodinsa. Para lograr el objetivo propuesto se trabaja bajo la siguiente metodología de diseño: primero, se determinan los parámetros de diseño de la máquina; luego, se estudia el estado del arte de las fatigadoras en el mundo. Finalmente, se diseña iterativamente los distintos subsistemas de la máquina. El resultado final de este trabajo incluye planos y memorias de cálculo del diseño, la definición de lógica de control de la máquina y un manual de utilización de la misma. El principal desafío en cuanto al diseño de la fatigadora es su versatilidad, ya que se requiere que sea capaz de ensayar cables desde 10 hasta 50 milímetros de diámetro. Dado lo anterior, el diseño de la máquina incluye dos poleas intercambiables que son utilizadas para tensionar el cable y originar su movimiento. El diseño final de la fatigadora es de disposición vertical. El movimiento del cable es inducido mediante la implementación de un motor servo de 75 kW acoplado al eje de una de las poleas. La carga del ensayo es suministrada por un cilindro hidráulico capaz de ejercer hasta 150 kN que cuenta con una carrera máxima de 812 mm. La combinación de los equipos mencionados permite realizar ensayos en el rango de diámetros de cable requerido sobre poleas de entre 200 y 1000 mm de diámetro. La adición de un sistema óptico de inspección permite automatizar la recopilación de datos generados durante la operación de la máquina y establecer la finalización de los ensayos según criterios de descarte existentes para cables de acero que operan en condiciones dinámicas.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in ful lment of the requirements for the degree of Master of Science in Engineering. June 2016 / It has been reported in literature that newly installed cable accessories can pass typical commissioning tests and yet show signi cant PD activity leading to premature failure in the long term. This research report details the partial discharge (PD) characterisation of three arti cial defects in MV cable terminations, at both power and very low frequency (VLF). The defects included a semi-conductor feather, a tram line in the cross-linked polyethylene (XLPE) insulation and an XLPE ring cut. The experimental methodology involved subjecting the terminations to a standard overvoltage withstand test, after which the PD activity was monitored, at 0.1 Hz and at 50 Hz excitation frequencies. All the defects passed the overvoltage test, despite some showing signi cant discharges. The defects gave distinct phase-resolved PD patterns that are e ectively invariant of excitation frequency. The PD magnitudes at power frequency were typically bigger than at VLF, while the PD inception voltages tended to be lower at VLF. The PD magnitudes of the semi-conductor feather defect surface discharges were found to increase with increasing applied voltage, while no increase was observed for the tram line and ring cut void discharges. The results show that common installation defects in MV cable terminations can be suitably characterised using VLF PD measurements / MT2016

Digitized by Kansas Correctional Industries

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: flow induced vibrations, nonlinear dynamics. Includes bibliographical references (p. 95-96).