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The importance of several problems has been emphasized by advances recently made in the thinking and operating techniques concerned with the maintenance of insulating liquids such as transformer oil. These advances are the direct result of a program of directed research conducted by a large group of power systems cooperating through a clearing-house laboratory and the are based upon the new concept...
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One of the main considerations in the manufacture of a Class “H” Insulation is the base material which is used as a carrier for the impregnating compound. To be suitable for high temperature electrical insulation, these base materials must be stable both physically and chemically at elevated temperatures up to 300°c.
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The great interest recently shown in the use of sulfur hexafluoride as a high-dielectric-strength gas has been accompanied by serious consideration of the possibility of the production of toxic and corrosive products in the event of electric breakdown of the gas. In this paper we shall formulate a mechanism for the decomposition and report our findings regarding the products formed under various conditions...
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The electrical characteristics of corona in air in the presence of dielectrics have been studied. The high frequency currents generated from this corona were investigated most intensively. The frequency spectra of these corona currents indicates that the corona losses are not confined to any narrow frequency region unless resonance exists due to circuit components. These same types of spectra were...
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The increasing use of gaseous dielectrics at elevated pressures is one of the significant trends in high-voltage engineering today. Such compressed gases can be superior to solid and liquid dielectrics and to high vacuum insulation, particularly for long gaps and high voltages.
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Twenty-five years ago we were satisfied with a simple distinction between “electric” and “thermal” breakdown which made temperature dependence the deciding feature. This standpoint became obsolete when we could show with more discerning methods that actually the alkali halides and other single crystals, while conducting thermally like iron, showed a very complex temperature dependence of the breakdown...
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This paper presents some of the anomalies in the dielectric strength of SF6 as a function of pressure and electrode separation in a non-uniform field. Over certain pressure ranges the a.c. voltage breakdown gradient may remain nearly constant or even increase with increasing electrode spacing rather than decreasing as normally expected. This yields unexpectedly high breakdown strength, characterized...
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One of the major problems in the use of polymeric materials is the degradation of these materials when exposed to certain service conditions. Recognizing this, a basic research program on the mechanism of the degradation of these materials was initiated at the National Bureau of Standards in 1946. The mechanisms of the degradation of polyamides and polystyrene have been studied. Polyvinyl chloride...
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Cellulosic materials deteriorate rapidly when exposed to temperatures above 100°C. for any considerable length of time. This limits their usefulness in electrical insulation at elevated temperatures. Synthetic fibers have been proposed as a substitute for cellulose in electrical insulation applications at elevated temperatures.
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Preliminary experiments have been conducted on the dielectric strength of polyethylene at microwave frequencies, with particular effort directed toward attaining the intrinsic strength. Thermal effects caused by dielectric heating are avoided through single r.f. pulses of microsecond duration.
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Storage of binary information in the stationary field of a ferromagnetic ring or a ferroelectric slab promises a neat solution to one of the most vexing problems in the digital computer field, the problem of “remembering” and making available a very large number of binary “words” rapidly and efficiently. The flux remanence and non-linear characteristics of the “rectangular” hysteresis loop simplify...
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From the variety of ferromagnetic oxide bodies developed during the last 15 years, a group of three which are of commercial importance is selected: the nickel-zinc- and nickel-copper-zinc ferrites, the manganese-zinc ferrites, and a newly found ferric oxide compound exhibiting a rectangular hysteresis loop.
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We have been studying the direct current conductivity changes in polyethylene during bombardment with photons of energy 1.2 Mev. The effect of this bombardment is to introduce a higher equilibrium conductivity in the material from that present without radiation. This conductivity arises from the additional charge in the material caused by the ionization by the γ rays.
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From 250 KVA through 2000 KYA, through 15 KV ratings, sealed-in-nitrogen Class H insulated transformers — the largest ever manufactured of sealed dry-type construction — have successfully eliminated fire and explosion hazards, These transformers are the choice of the Factory Insurance Association for indoor usage. A 2000 KVA transformer weighs tons. In its construction, 1100 pounds of glass fiber-silicone...
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The prime function of the A.S.T.M. is the development of practical test standards and specifications for commercial use. Pure research is not one of its objectives, but in devising new standards and revising them to keep pace with improvements in the art, much work of a research nature is required. The A.S.T.M. approach is that of the engineer, whose chief concern is evaluation of breakdown in terms...
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A crucial test of any theory of electrical breakdown is the comparison of observed and predicted temperature dependence of the electric strength. The theories of von Hippel, Seitz, and Callen give the proper temperature dependence at low temperatures (for ionic crystals) but the agreement is lost at high temperature. In order to explain the high temperature region, Fröhlich has adduced another breakdown...
