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One of the objectives of the Signal Corps sponsored research program on ceramic dielectrics is to improve the impact resistance of high frequency ceramic dielectric insulation. The fundamentals involved indicated that increasing physical strength and decreasing modulus of elasticity should increase impact resistance, however, an analysis of the available data for these properties indicated that both...
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A corona discharge can be detected electrically with a resistor or inductor in series with the test gap. The corona current pulse causes an electric oscillation in an inductance or a single sharp voltage pulse across the resistor. The disadvantage of this means of detection is in the interference from a signal which may be created across the inductance or resistance by corona or contact sparking outside...
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Experience in presenting a paper on the subject at the 1954 Annual Meeting of the NRC Conference on Electrical Insulation indicates that additional background information on high temperature materials and additional tests on models are desired. Functional testing is rapidly gaining momentum in acceptance.
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Solid and gaseous dielectrics are both used for electrical insulation, either singly or in combination. Where solid is used as a major component, the detrimental effect of gases, such as air voids, has been discussed at length by various investigators. However, little has been reported on the effect of solid materials to the gaseous insulation. With the recent uprising trend of using gaseous dielectrics...
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Several unexpected dielectric effects have been observed when certain organic compounds are solidified in electric or magnetic fields. When solidified in electric fields either alternating or uni-directional, the dielectric constant of these compounds in the solid state becomes higher than normal. For example the constant of a dielectric material called Nitrowax* can be increased over 70% by solidifying...
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Organic insulations composed of paper or cloth base with phenolic or black asphaltic varnish impregnant are shown by extensive tests to have an aging rate in air dependent on the insulation thickness. A change in insulation thickness from that representative of turn insulation to that used for a major voltage barrier may increase its useful life in air by as much as ten times if in a dry atmosphere...
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The purpose of these studies was to investigate the source of noise which is generated when thin dielectrics are subjected to relatively low D.C. voltages(1,2). If the measured noise voltage is caused by the movement of ions or electrons in the volume of the dielectric between electrodes as shown by Haworth and Bozorth(3), then a semi-quantitative measurement of this noise might be a means whereby...
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The volume conductivity of polyethylene terephthalate films has been measured as a function of temperature in the range 65° to 150°C.; as a function of voltage in the range 1 to 1000 volts/mil; and as a function of film variables such as orientation and/or crystallization. Supplementary dielectric constant and loss measurements were also made. Previous work by Amborski(1) has defined the high temperature...
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Successful dielectric measurements on soda lime glasses at frequencies down to 0.1 cycle per second were made by Stevels in 1953 at the Philips Research Laboratories. He used a phase shift oscillator directly coupled to a simple resistance-capacitance bridge. A long period galvanometer was used as a null detector.
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This talk is available as Technical Report No. 101, Massachusetts Institute of Technology and will appear in a forthcoming issue of Fortune Magazine.
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The susceptibility to carbon tracking upon exposure to electrical arcs has always been a fundamental weakness of organic insulations. Although recent emphasis has teen on the development of organic materials with more versatile physical characteristics and improved high-temperature properties, comparatively little work has been published on compounding materials to specifically resist tracking under...
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From the results of this work, it seems that the actual mechanism of breakdown of an insulating oil is critically dependent upon the duration of the applied voltage pulse, and the magnitude of the hydrostatic pressure.
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A dynamic technique for studying the pyroelectric effect has been developed. Pyroelectric current pulses of approximately square waveform are produced in pyroelectric crystals when they are illuminated with intense chopped light from a tungsten lamp. During a light pulse the crystal temperature, T, rises, thus causing the polarization, P, to change at a rate determined by the product of the pyroelectric...
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This instrument was developed as a solution to a problem which arose in our research on conductivity in rutile single crystals. In attempting to identify the origin of the charge carriers in the temperature range below 400°C, it was felt that photoresponse measurements would provide a clue. With illumination in the 1 micron region, a small transient photo current was observed with a d-c amplifier...
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During the course of the Southwest Pacific campaign it was found that many of the insulations in use at that time were particularily susceptible to attack by fungus growth. As a result of these findings specifications were written by the armed services relative to the fungus resistant properties of these materials. Procedures for testing these properties were devised and the one that is accepted at...
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Two years ago at this Conference we presented a paper in which it was demonstrated that the sparking potentials of simple hydrocarbon gases could be related directly to certain physical properties of the molecules of which the gases were composed(1). In order to accomplish this it was first necessary to derive an expression relating the first Townsend coefficient, α, of a gas to the pressure, P, the...
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In our investigation of the mechanism of electric breakdown in liquids, we have endeavored to measure a value for the electric strength that is characteristic of the liquid itself; ideally, that value which is free from the influence of all external factors such as electrode composition, surface condition, and configuration. However, because the influence of such factors as these cannot be completely...
