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 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.

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

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: nuclear power plant; electric cables; fire. Includes bibliographical references (p. 70-75).

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

No description available.

A dissertation submitted in fulfilment of the requirements for the degree of Master of Science in Engineering to the Faculty of Engineering and the Built Environment, School of Electrical and Information Engineering, University of the Witwatersrand, Johannesburg, 2018 / Power cable terminations and joints experience high electrical stress due to the abrupt change in geometry of the cable; hence the insulation at these points is more prone to partial discharges and has been reported as the main root cause of power cable system failures. Electrical failure of the insulation is known to occur due to a phenomenon of Partial Discharges (PD). Modern practice (especially in higher voltage installations) entails installation of PD sensors at strategic locations during installation of electrical equipment such as cable joints and terminations. This enables continuous monitoring of PD events in the plant, and this is termed on-line PD diagnosis. However, with limited knowledge to interpret the meaning of certain PD changes during the service period, this practice remains limited. It is therefore the interest of the study to understand the time evolution behaviour of PD characteristics in order to discern the insulation condition or deteriorating stages. The present study is on XLPE power cables, focusing on PD in artificial defects in the cable termination insulation that in most cases arise from poor workmanship. The power cables were subjected to accelerated ageing to emulate their ageing under service conditions. PD measurements were then conducted at periodic time intervals and characterized PD in terms of PD Inception Voltage (PDIV), maximum apparent PD magnitude (Qmax), Pulse Repetition Rate (PRR) and Phase-Resolved-PartialDischarge-Pattern (PRPDP). The findings are that, Qmax, PRR and PDIV did not show any time-evolution trends unique to a defect, the general trends observed were that of a fairly constant PDIV with several fluctuations of a 5 kV band. Qmax showed a decreasing trend over ageing time. The PRR decreased overall, with a pick up increase near the end of the tests. Qmax and PRR were noted significantly fluctuative between 23% and 57% of the total ageing period, distinct characteristics were that, the tram line had the largest PRR which is expected since it is a flat cavity, and iii the PRPDP appeared more skewed than other defects. The semicon feather had a PRPDP that seemed like a combination of a void discharge and corona discharge. The ring cut PRPDP was similar to that of the tram line except that it was not skewed. Furthermore, a capacitance PD model was constructed in Matlab R Simulink R to emulate experimental observed PD behaviour and therefore confirm the theory explaining the observed time-dependency of PD phenomena. Simulated void discharge PRPDP which corresponded with experimentally measured PRPDP were obtained for the unaged, moderately aged and severely aged cavity defect. The corona-surface discharge effect observed in the semicon PRPDP was also successfully emulated. The study outcomes suggest that PD characteristics evolve over time, and that the behaviour of the observed trend is unique at different stages during ageing. The time evolution characteristics of PD are The PRPDP signatures did not change with time of ageing despite the variations in Qmax and PRR. This means that, defect signatures obtained prior ageing or in-service operation of the cables can still serve as a good reference of identifying the nature of the defect at different ageing stages except in the event of PD evanescence. From the simulations, it was derived that the PD region surface conductivity as well as the geometry of the defect are the main contributing factors to the unique signatures observed at different stages and per defect. / XL2019

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No description available.