In areas supplied by underground transmission systems load division among several parallel connected cables may not be satisfactory. Phase-angle-connected TCUL transformers may be used to provide the phase shift necessary to equalize the cable loading and to provide voltage regulation at the load. A means for automating the TCUL adjustments to provide satisfactory current balance and voltage regulation was sought. This problem was attacked by first expressing the system performance (the unbalance of cable currents and load voltage magnitude) in terms of a system performance function. An optimal policy of control is defined as the selection of the particular TCUL transformer which provides the greatest improvement in the system performance. A negative gradient optimization routine is used to determine the required adjustment. A derivation of the adjoint network relationships for a phase-angle-connected transformer is given. These relationships provide a means for readily determining the gradient of the performance function. This approach is developed to provide a means for continuously monitoring and automatically controlling the system performance. A discussion of two ways in which this approach might be implemented physically is given. The optimally adjusted TCUL controller was incorporated in a digital computer model of a small underground power system. Simulated operation of the system under widely varying load conditions demonstrated the ability of the controller to maintain very small cable current unbalance while simultaneously holding voltage variations to +2.9 percent of nominal. A significant advantage of this approach is that the optimal sequence of adjustments required to restore the system to a satisfactory level of performance may be obtained and verified without making any actual adjustments to the TCUL transformers. This is important from a maintenance point of view. A possible disadvantage of the method is that an accurate model of the system must be available. / Ph. D.

Thesis--Ph. D., University of Hong Kong. / Mimeographed.

(Uncorrected OCR) Abstract of thesis entitled liField analysis in power supply lines by integraJ. equation methodll subm1 tted by FOe, PIK YlJE for the degree of Ph.D at the University of Hong Kong in December, 1974. Abstract In this thesis, the integral equation (I.E.) method has been employed successfully to solve field problems in power supply lines. Though the I.E. method is mathematically quite involved, it is shown that it is possible to treat the integral equation as a system of linear equations. Hence the transformed simultaneous linear equations can be considered as the starting point for solving problems either in overhead lines or \Ulderground power cables. In overhead lines, especially in Extra-High-Voltage and Ultra- High-Voltage systems, an evaluation of the electric field near each conductor, especially the maximum electric field, is essential as corona and radio interference become important considerations in the design of such lines. The I.E. method has many advantages over the other existing methods in calculating the potential gradient at the surface of the overhead lines in that it yieldS reasonably accurate results with comparatively simple numerical computations. The difference between the present method and the existing methods is the basic assumption. In the I.E. method, subconductor surfaces are treated as equipotential lines whereas in other existing methods, the subconductor surfaces usually do not coincide with the simulated equipotential lines. The method can also be applied equally well to symmetrical or asymmetrical bundle conductors with or without ground wires. Other parameters such as capacitances, potential gradients at the earth surface etc. are also included in the computer program. In underground cable systems, the I. E. method proves to be very effective in tackling the thermal field problem, especially when the cables are buried shallow and thus the earth i s surface can no longer be treated as isothermal. .It has been found that the thermal resistance (external) obtained wi::;h a non-isothermal earth surface is considerably higher than that obtained under the assuumption of an isothermal earth surface. With non.-isothermal earth surface, the temperature difference on the earth surface between the spot vertically above the cable and the spot at a distance eClual to twice the depth of burial of the cable away could be as high as lOoe. The finite-difference or fini te-搪lement method could likewise be used to solve the problem of a non-isothermal ea>:>th surface, but the computer storage re'luired and the execution time would be much more than that using the I.E. method. / abstract / toc / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The majority of Eskom's 22kV lines use wood as the support structure material. The economics of wood pole cross arms and their flashover withstand capabilities outweigh those of steel cross arms. However, wood pole structures are vulnerable to what is known as a Pole Top Fire. When insulators and wood cross arms become polluted, small and sustained leakage currents flow along the surface of the insulator and thereafter into the wood itself. This eventually leads to burning of the wood. Many of the 22kV lines traverse vast rural lands, going over people's path ways. If this fire is not discovered timeously, it can cause breakage of the relevant cross arm or the pole itself. A broken cross arm usually causes the outer phase conductor to hang between one and two meters above ground. When it's dark, rural inhabitants cannot see clearly and walk directly into these low lying energized conductors which cause severe injuries and often fatalities. Low hanging conductors cannot be detected electrically and are potentially hazardous to humans and animals. Safety is currently one of the highest priorities for Eskom Distribution and hence there is a dire need to mitigate Pole Top Fires. The researcher hypothesizes that the implemented mitigating technique of bonding does not eliminate Pole Top Fires. In this study accurate statistics on Pole Top Fires in KwaZulu - Natal are provided and causes of fires investigated to provide an understanding thereof. Two basic mechanisms of burning have been identified and explained. These are surface tracking and sparking, and internal sparking. This has helped to explain what mitigation techniques will be effective. A critical analysis on the performance of recommended mitigation techniques is conducted. This study therefore aims to conclude on the effectiveness of implemented techniques to mitigate Pole Top Fires. By comprehensive and critical analysis of a complex operational and safety related problem technical options for mitigating or eliminating the fires are identified, critically analyzed and only those options that are really technically feasible are proposed. This has not been properly done in Eskom before. It is within this context that this research has been undertaken. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

Power line function is to transfer electrical power. Power lines represent a major component in the transport process of electricity and they are subjected to various types of failures. Causes of failure include wind-induced oscillations or Aeolian vibrations. Wind causes transmission line conductors to undergo oscillatory motions which cause failure. To mitigate oscillations of line conductors, Stockbridge dampers are used. It has been observed that dampers are subjected to the same undesirable and destructive effects from vibrations as the conductors they are meant to protect. In the case of a damper, the cyclic bending as well as the friction between its wire cables are caused by vibrations leading to failure. The mathematical model describing the bending stress of the symmetrical Stockbridge damper’s messenger cable near the clamped end is analyzed. The reliability of the mathematical model is assessed using experimental data obtained from the forced response test conducted at the VRTC laboratory at the University of KwaZulu-Natal, Durban. Data from the experiment has been compared with the MatLab model established by the researcher. Due to friction between the wires of the messenger cable, variation of temperature is observed in the messenger cable during operation. Change of temperature of the messenger cable was investigated, as a function of time, at constant velocity and constant displacement. Experimental data were generated during dynamic characteristic tests on Stockbridge dampers and thereafter the prediction of the variation temperature was undertaken. There are various mechanical characteristics of a damper that can be affected with time. To reach the aim of this study, three types of vibration test were conducted on the Stockbridge damper: the fatigue test, the forced vibrations test and the free vibrations test. Tests were conducted on a shaker machine with new and used Stockbridge dampers to determine the remaining life of those dampers by looking at their different mechanical properties. The frequency domain and time spectrum were used to display the results. The fatigue test investigated one of the commonest types of Stockbridge damper failure, namely, loss of the small mass because of sustained high frequency resonance. Ultimately, data correlated well and two mathematical models were developed: one for predicting damage in the life of a Stockbridge damper (based on the highest resonance frequency of the damper), and one for predicting the temperature of the messenger cable. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

No description available.

Thesis (Ph.D.)--Victoria University (Melbourne, Vic.), 2009.

Thesis (MScEng)--University of Stellenbosch, 2001, / ENGLISH ABSTRACT: A frequency domain Power Line Carrier (PLC) simulation program, with the ability to simulate signal attenuation including the coupling equipment, was developed. This simulation program was put to the test against the independent program of Professor L.M. Wedepohl and against practical field measurements. The predictions of the two programs were in precise agreement for a wide range of input parameters. Results from the field tests and predictions also showed close agreement. Further investigations, applying the simulation program, explained how ground conductors and soil resistivity influences PLC signal propagation. An experiment, which was developed to monitor PLC signal attenuation, was installed on the PLC system between Koeberg power station and Acacia substation, both near Cape Town. Data logged continuously over 28 days, indicated measurable and deterministic PLC signal attenuation variations with typical time constants of a few hours. Simulations of the PLC system indicated that the signal amplitude variations were influenced by changes in the height above the ground plane of the phase conductor. This significant finding creates the possibility to obtain real time knowledge of the sag of an Over Head Transmission Line (OHTL) by exploiting an operational PLC system. The knowledge about real time sag can be used in economical dynamic ampacity control systems. The practical and financial benefits to the electricity supply and distribution industry can be significant. / AFRIKAANSE OPSOMMING: 'n Frekwensie gebied "Power Line Carrier" (PLC) simulasie program wat die sein verswakking en die koppeling verliese kan naboots, is ontwikkel. Die program is getoets teen die onafhanklike program van Professor L.M. Wedepohl asook praktiese metings in die veld. Die vooruitskatings van beide programme is presies die selfde vir 'n wye reeks van parameters. Metings en nabootsings het ook noue ooreenstemming getoon. Verdere ondersoek, m. b. v. die program, is gedoen ten einde te verduidelik hoe grond-geleiers en grond weerstand die PLC sein se voortplanting beïnvloed. 'n Eksperiment om die PLC sein se verswakking mee te monitor is ontwerp. Die eksperiment was geïnstalleer in die PLC stelsel tussen Koeberg kernkragstasie en Acacia substasie, naby Kaapstad. Die eksperiment was vir 28 dae geaktiveer en die data wat die eksperiment opgelewer het toon meetbare PLC sein verswakking met tyd konstantes van 'n paar uur. Verdere nabootsings het gewys dat die veranderende verswakking in die PLC seinsterkte toegeskryf kan word aan die wisseling in hoogte van die fase geleiers bo die grondvlak. Hierdie bevinding is van besondere belang aangesien dit die moontlikheid oopmaak om die gemiddelde sak van kraglyne in reële tyd en onder bedryfs toestande te kan meet. Die informasie van die reële sak van kraglyne kan gebruik word in effektiewe stroomdrae-vermoë beheer stelsels. Die praktiese en finansiële voordele wat krag voorsieners en verspreiders hieruit kan put kan aansienlik wees.

M.Sc. / The transmission system of Eskom occupies approximately 28 000 km of servitude that crosses a number of biomes in South Africa. The management of these servitudes, with respect to the impacts that the system has on the surrounding environment, as well as the effect of biotic, social and natural phenomena on the electrical system, needs to be carefully managed. This study investigates these bi-directional influences to determine which are pertinent to the management to the transmission line servitudes. This study also derives a number of strategic actions and accountabilities for all participating departments in the Transmission Division of Eskom, who are involved in the management of one or more phases of the life cycle of the servitude.

Thesis (PhD) -- Stellenbosch University, 2004. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: The radio noise (RN) performance of an AC high voltage transmission line is a determining factor when accessing the reliability of the design. The conducted RN level across the terminals of a PLC receiver, used in the teleprotection system of the line, is of particular concern. In this dissertation, existing empirical and semi-analytical RN prediction methods are evaluated by comparing the conducted RN levels of four South African lines to the predicted levels. Existing RN measurement protocols are consolidated and a new RN measurement protocol is proposed for the comparison. A prediction methodology, based on the EdF, EPRI and IREQ semi-analytical methods, is formulated. The semi-analytical methods are not able to accurately predict the variation of the conducted RN with frequency in the PLC band, nor are they able to predict the RN performance of short lines. A wideband excitation function, which considers the statistical characteristics of the measured RN pulse train, is therefore proposed in this dissertation. Having investigated the extraction of this excitation function from ESKOM’s Megawatt Park corona cage, it is concluded that a small corona cage is required. The design of a small cage is presented and the extraction of the excitation function is described. Attention is given to assessing the effect of changes in space charge distributions. The effect of space charge collision with an insulated cage on the extracted pulse parameters is linear, provided space charge diffusion is negligible. The onset streamer, positive streamer and negative streamer corona modes were identified as the only modes with measurable RN in the frequency regime 150 kHz to 30 MHz. Formulas are derived for the prediction of the inception gradients for these modes. The RN performance of an ACSR Hare conductor is extracted from the small cage. The RN performance of the Acacia-Koeberg line is also approximated in the PLC band. The dissertation concludes that the proposed wideband excitation function method is capable of accurately predicting the variation of RN levels with frequency. It can also be used to predict the RN performance of short line sections, as well as the relationship between RMS, QP and average RN levels from a transmission line. / AFRIKAANSE OPSOMMING: Die korona-werkverrigting van ‘n WS hoogspanningstransmissielyn het belangrike gevolge vir die betroubaarheid van die ontwerp van die lyn. Die geleide radioruis (RR) vlak op die kraglyndragolf kommunikasie sisteem, wat vir tele-beveiliging gebruik word, is veral van belang. In hierdie werkstuk word bestaande metodes gebruik om die korona-werkverrigting te bepaal en dan met gemete waardes van vier Suid Afrikaanse lyne te vergelyk. Bestaande RR meetmetodes word saamgevat en ‘n nuwe metingsprotokol word voorgestel om resultate te vergelyk. Na aanleiding van hierdie vergelykings word ‘n tegniek ontwikkel om die RR van ‘n lyn te voorspel. Hierdie tegniek gebruik die EdF, EPRI en IREQ metodes. Die voorgestelde tegniek kan nie die verandering van die RR met frekwensie bepaal nie. Dit kan ook nie die RR van kort lyne bepaal nie. ‘n Wyeband RR bron word dus voorgestel. Nadat ESKOM se Megawatt Park korona-kou ondersoek is, is die gevolgtrekking gemaak dat ‘n klein koronakou die nodige wyeband RR bron sal voorsien. Ruimtelading bots met die klein korona-kou. Die effek van hierdie botsings op die pulsparameters is lineer indien ladingsdiffusie nie plaasvind nie. Die aanvangs, positiewe en negatiewe kanaalontladings (“streamers”) is identifiseer as die enigste koronamodusse wat RR veroorsaak tussen 150 kHz en 30 MHz. Die spanning waarby hierdie modusse voorkom, is bepaal. Die korona-werkverrigting van ‘n “ACSR Hare” geleier is bepaal. Die korona-werkverrigting van die Acacia-Koeberg transmissie lyn is ook gekwantifiseer by die kraglyn-dragolf kommunikasie frekwensies. Die wyebandbron metode kan die verandering in RR met frekwensie goed voorspel. Die nuwe metode kan ook gebruik word om die RR van kort lyne te bepaal, asook die verband tussen RMS, QP en gemiddelde RR vlakke.