Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 94-96).

Thesis--Swiss Federal Institute of Technology. / Vita. Bibliography: p. 87-93.

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (DR. ENG.)--Johns Hopkins University, 1935. / Cover title. Vita. "By J.B. Whitehead ... [and] S.H. Shevki." "Reprint from Electrical engineering ... June 1935 issue." Bibliography: p. 7.

Thesis (D. ENG.)--Johns Hopkins University, 1934. / Cover title. Vita. Caption title: Dielectric properties of cellulose paper ... by J.B. Whitehead ... [and] E.W. Greenfield ... Bibliography: p. 8, 14.

Thesis (Ph. D.)--Anōtatē Scholē Ēlektrologōn Mēchanikōn E.M. Polytechneiou, 1981. / Summary in English. Includes bibliographical references (p. 139-142).

The deterioration of electrical insulating oils results in the formation of complex oxidation products, many of which are polar in structure. The significance of the microwave-frequency dielectric-loss measurement, when applied to the evaluation of aged transformer oils, is investigated. A cylindrical cavity, operating in the TE₀₁ mode, is used to measure the loss tangent of aged transformer oils. Q-factor measurements are made by a dynamic method which is described. The problem of mode interference in the cavity is investigated in detail. It is found that the loss tangent of transformer oils, measured at X-band, increases as the oil deteriorates through oxidation. The increase is influenced by several factors but closely parallels the increase in acidity. Sludge particles do not in themselves cause a significant increase in the dielectric losses. An indirect correlation between the loss tangent and the sludge content of an oil may exist but has not been established. The change in the dielectric constant of an oil caused by the presence of dissolved water, or by the ageing process, is too small to be measured by the method used. A small but measureable increase in the loss tangent is produced by the presence of water in concentrations of approximately 75 parts per million. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The work contained in this thesis is concerned mainly with conduction mechanisms and polarization processes in thin amorphous insulating films. A model has been proposed and its d.c. conduction characteristics computed. The numerical results show the possibility of obtaining either space charge, Schottky, or Poole-Frenkel characteristics depending on the model parameters. The transient electronic discharge current has been analysed and the results show that this electronic current is approximately independent of the preapplied voltage in contrast to the ionic discharge current which is linearly dependent on preapplied voltage. This result, together with the experimental results obtained on Ta/Ta₂O₅/Au diodes, suggests that the calculations of low frequency dielectric losses using step response measurements are complicated by space charge effects only when the preapplied field is relatively low (≤lMV/cm for Ta₂0₅ films). Ta/Ta₂O₅/Au diodes were prepared by solution anodization or plasma anodization. All prepared diodes exhibited a rectification behaviour. Over the frequency range 100 Hz -100 kHz capacitance and loss tangent were found to decrease slightly with increasing frequency while the equivalent series resistance was found to be approximately proportional to ω⁻¹‧º⁵. All prepared diodes, with gold counter electrodes less than 1000 Å thick, were found to withstand, under a slowly applied field, field strengths approaching the formation field value. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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

by Poon Ming-Cheong. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves [163-175]