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This paper presents the results of needle tests conducted on 15 kV polyethylene insulated cables. The tests were performed for metal needle electrodes as well as for gas point electrodes (pinholes).
This paper first treats confirmation on that moisture absorption behavior of XLPE (crosslinked polyethylene) satisfies Fick's equation and relates the effects of moisture absorption and temperature on water tree in XLPE under water. Secondly, the results of experiments and the considerations on them related with the findings about water trees in humid air and in epoxy resin are described. By a few...
This paper reports recent results in a continuing ESR study of free radicals in electrical trees in polyethylene (PE). Data pertaining to three different kinds of PE are presented: commercial cable material (XLPE), and two low density materials (LDPE), one relatively impure, the other of high purity (HPPE). It is found that the saturation behavior of the absorption lines is particularly useful for...
Particles influence both AC and DC voltage breakdown in insulating oil. Larger and conducting particles decrease the breakdown voltage most. For both DC and AC the ratio of breakdown voltage for clean oil to oil with non-conducting particles is nearly the same. For conducting particles the ratio for DC is generally larger than for AC. Particle concentration and motion is influenced by DC and AC stress...
The major components of the insulation system in oil-filled transformers and allied electrical equipment are paper, wire enamel, and the oil itself. The degradation of any one of these materials may affect the degradation and hence the performance of the others. The work reported here was undertaken in an attempt to assess the affect on the degradation of these components of a change from transformer...
Since World War I, electrical insulating oils for transformers and allied electrical equipment have been refined from naphthenic petroleum crude oil stocks. The resulting oils have had acceptable dielectric, mechanical and heat transfer properties and little or no wax formation occurs at temperatures down to −40°C. Usable naphthenic crude oils appear to be coming into short supply and there is a real...
From a statistical viewpoint, the problems associated with “strength of materials” as applied to different states of matter and different phenomena such as mechanical strength or electrical strength are all essentially equivalent. This assumes that we conceive the materials as being permeated by small defects spread randomly throughout the material. These defects cause local weaknesses which may reduce...
Experimental results are reported on the chemical decomposition of Methyl and Phenyl substituted Polysiloxanes under the action of partial discharges and discharges. Gas analysis was carried out and the gas composition was determined as a function of the discharge conditions and of the molecular structure of the oil. Measurements on charge carrier injection and breakdown in inhomogeneous fields were...
A brief review of the aging behaviour of oils of different quality under operating conditions is given. Simultaneous tests of numerous samples of oils of various type origin and quality were performed. The testing methods used are briefly described and the interpretation of the experimental results is given in tabular and graphical form. An analysis is given of the aging stability of oils samples...
Accurate knowledge of the thermophysical properties of dielectric liquids is essential to give a datum upon which to establish the probable thermal performance of apparatus using any proposed substitute. The thermal conductivity of a selection of natural mineral oils used in transformers and cables has been measured by the transient line source method. The interesting observation emerges that in a...
It is shown that a direct voltage component is obtained when measuring the surface field strength of a polyethylene sample which is tested under an alternating voltage stress. So far this effect cannot be explained, but it is assumed that it is connected rather with solid-electrode interface phenomena than with solid-bulk parameters.
This paper summarizes the progress of an extensive study of the ac voltage endurance, extending from a single cycle to more than a year, for cast silica-filled epoxy resin, with recessed silver paint electrodes and cast-in aluminum electrodes, giving a nearly uniform electric field. Although the specimens were prepared to avoid gas cavities, and partial discharges were usually undetected, the ac strength...
This paper describes an integrated field and laboratory test program conducted to determine the basic degradation process of new high voltage insulating materials (i.e., grease, polymer, semiconducting glaze) under outdoor life conditions. The field tests were conducted on rod samples at Southern California Edison's Mandalay Insulator Test facility; while laboratory studies were performed at the University...
Accelerated aging tests on high-voltage solid insulation can be correctly interpreted with a convenient technique recently developed for the analysis of Weibull statistical data. Examples illustrate the significance of this technique in making valid comparisons of expected service lives on the basis of such tests.
Strong electromagnetic fields exist in the region of the windings of large electrical machines. The structure which supports the windings must be capable of taking overloads arising from abnormal operating conditions. Glass fibre reinforced plastics (GRP) are nonmagnetic, electrically insulating and have high mechanical strengths over a wide range of temperature. Insulating components for supporting...
Changes of the superficial properties of epoxy resin compositions with Al2O3 and SiO2 fillers were investigated in dry SF6 decomposed under the effect of the electric arc. The influence of electrode material, of small moisture and air content as well as of the presence in the test space of materials containing silicon upon the change of superficial resistivity and the structure of superficial strata...
Progressive degradation of high-voltage generator insulation whether due directly to the erosive effects of internal or slot discharge, or to other debilitating factors such as heat and vibration, may be detected and monitored as a function of time by in-situ partial-discharge tests. This paper describes new diagnostic test techniques for assessing the condition of generator insulation with a minimum...
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