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Electrical Insulation, IEEE Transactions on

Issue 1 • Date Feb. 1977

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Displaying Results 1 - 19 of 19
  • Table of contents

    Publication Year: 1977 , Page(s): c1
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    Freely Available from IEEE
  • IEEE Electrical Insulation Group

    Publication Year: 1977 , Page(s): c2
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    Freely Available from IEEE
  • Editorial

    Publication Year: 1977 , Page(s): 1
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  • Treeing in Solid Extruded Electrical Insulation

    Publication Year: 1977 , Page(s): 2 - 18
    Cited by:  Papers (60)  |  Patents (1)
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    A survey of the literature on the subject of treeing in solid dielectrics is presented. The purpose is to provide an introduction to the subject, some background for the current research work, and a list of references to some of the more rigorous treatments which in most cases have a narrower scope. The trees which grow in insulating materials can be considered in three classifications; electrical trees, water trees, and electrochemical trees. They are all initiated at sites of high and divergent electrical stress and may be aggravated by the presence of moisture, chemical environment, and contaminants. It has been shown that trees will grow in any organic dielectric under appropriate conditions. However, the major portion of the work sUmmarized here has been carried out on polyethylene. This is not because polyethylene is most subject to treeing, but because it is the most popular modern insulating material. It has excellent electrical properties, and an enviable service record. Recent development of improved constructions for electrical insulating systems, including high voltage power cables, and research on formulation of materials and voltage stabilizing additives have shown that improved resistance to treeing is possible. View full abstract»

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  • DC Treeing Breakdown Associated with Space Charge Formation in Polyethylene

    Publication Year: 1977 , Page(s): 19 - 25
    Cited by:  Papers (49)
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    It is well known that space charge accumulation has a great influence on both the short-time and long-time breakdown strengths of plastic insulation systems operating under direct voltages. In this paper, dc treeing phenomena initiated from the tip of a needle electrode inserted into a polyethylene specimen have been investigated under various conions. The characteristics of four kinds of trees, dc tree, short-circuit tree, polarity reversal tree and impulse tree, were investigated as a function of the voltage-rising speed, period of dc prestress, time before the short-circuit or the application of a voltage of reversed polarity, impulse voltage, needle electrode material and temperature, etc. Also, thermally stimed current (TSC), thermoluminescence (TL) and photo-induced current techniques were applied to estimate the nature of the trapped carriers and carrier trapping centers. From the experimental results, it was concluded that a homo-charge is formed at high electric stresses and that the homo-charge induces an electric field distortion around the needle tip. In order to explain the length of the tree as a function of the various factors mentioned above, a model for the space charge formation is proposed, including the process such as charge injection, trapping and its diffusion. View full abstract»

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  • Tree Initiation in Polyethylene by Application of DC and Impulse Voltage

    Publication Year: 1977 , Page(s): 26 - 30
    Cited by:  Papers (16)
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    The results of tree-initiation tests using impulse voltages show that the time required for the build-up of space charge at 25C is 30¿s~80¿s. The results of prestressing tests with DC and superimposing impulse voltages show that the space charges are homo-charges. An investigation of tree-initiation in polyethylene was carried out using dc and impulse voltages, the latter having a wave-front duration ranging from 1 ¿s to 700 ps. The relationship between the tree-initiation voltage and the duration of the wave-front of the impulse voltage shows that the times required for the build-up oif the space charge at the tip of a needle electrode are 30¿s~140¿s at 40C for both polarities and greater than 700 ¿s for the positive needle and 80¿s~l40¿s for the negative needle, respectively at 60C. The tree i Ltiation voltage decreases when the impulse voltage is superimposed on a dc voltage of the opposite polarity and increases when the impulse voltage and the dc voltage are of the same polarity. Some of the samples were prestressed with dc voltage for 10 minutes, and were then subsequently tested by applying an impulse voltage with a wavefront duration of 1 ¿s after a waiting period of 2, 30 and 60 minutes, respectively. The tree-initiation voltage was reduced in a similar manner as when an impulse was superimposed on a dc voltage of opposite polarity. View full abstract»

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  • On the Mechanism of Tree Initiation

    Publication Year: 1977 , Page(s): 31 - 34
    Cited by:  Papers (13)
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    Although the dc-tree-initiation voltage at a needle electrode in a plastic is very high, a tree can be formed by grounding the needle after charging it with a much lower dc voltage than the tree-initiation voltage. The tree formed by grounding will be called "a grounding tree". Since the formation of a tree under ac voltages is considered to be due to the repetition of charging and discharing, some relationship may exist between the ac tree and the grounding tree. The tree-initiation observed with a voltage composed of dc and ac shows that it is caused by a nearly constant value of the ac component, irrespective of the magnitude of the dc component. This also indicates that the mechanism of the intiation of an ac tree and that of a grounding tree are similar. An explanation is also given as to why the tree shape is branch-like or bush-like with ac voltages. View full abstract»

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  • Initiation of Internal Discharged in a Liquid-Nitrogen-Filled Cavity

    Publication Year: 1977 , Page(s): 35 - 39
    Cited by:  Papers (4)
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    Discharge initiation phenomena in a liquid-nitrogen-filled cavity were investigated using "ac impulse" i.e., the initial rise of a 50 Hz voltage wareform. It was found that the discharge magnitude in the beginning half cycle of the voltage was either greater, equal, or smaller than that observed in the next half cycle. This phenomenon is discussed in terms of discharge processes and the quantity of discharge-formed bubbles. Overvoltage characteristics of the discharge magnitude were found in both liquid and gaseous nitrogen filled cavities. A semi-empirical formula has been derived which corrlates the discharge magnitude and overvoltage. It was also shown that liquid nitrogen discharges are accompanied by luminescence. View full abstract»

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  • Treeing of Polyethylene at 77K

    Publication Year: 1977 , Page(s): 40 - 45
    Cited by:  Papers (18)
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    Ac tree starting voltage of low density polyethylene has been found to be higher at liquid nitrogen temperature (42kV) than that at room temperature (7kV) and it is almost equal to the positive impulse tree starting voltage. This improvement may be due to either the partial-discharge free contact of the interface between the needle electrode and the polyethylene and for the moderation of the intense field at the needle tip by injected space charges. The space charge injection was examined by evaluating the dependence of impulse tree starting voltage on the rise time of the impulse voltage, and the dc prestress effect on impulse tree starting voltage. It was estimated from the peculiar shape of the impulse tree that the injection depth of space charge is about 10 ¿m. The electroluminescence produced at the needle tip by ac voltage application was found to be completely different from the corona discharge in a void and it was explained by the radiative recombination process of space charges injected alternately. View full abstract»

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  • AC Dielectric Performance of Helium Impregnated Multi-Layer Plastic Film Insulation

    Publication Year: 1977 , Page(s): 46 - 50
    Cited by:  Papers (3)
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    Several types of thin polymer film insulation are being evaluated for possible use in superconducting underground transmission cables. Measurements are reported on the partial discharge inception voltages of threelayer disc samples of 102-¿m polyethylene and 61-¿m polycarbonate for temperatures and pressures of the helium impregnant ranging from 5.0 K and 0.3 MPa to 11.5 K and 1.5 MPa. Butt gaps are simulated by punching 1 mm diameter holes in some of the layers. The effect of aluminized shielding around the holes is discussed. The observed inception voltages vary strongly with the helium conditions, increasing rapidly as the density increases. The results suggest that the voltage is capacitively divided between the polymer layers and helium-filled gaps, with partial discharge occurring when the breakdown strength of the helium is exceeded. View full abstract»

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  • Measurement of AC Insulation Losses at Cryogenic Temperatures

    Publication Year: 1977 , Page(s): 51 - 54
    Cited by:  Papers (2)
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    The design of superconducting high voltage transmission lines requires engineering data which, until recently, have been largely unavailable. The selection of a suitable dielectric for a tape-insulated ac cryogenic cable, for example, requires the knowledge of insulation dissipation fagtors at high voltage, which are typically 20 x 10 or smaller. We present here dissipation factor measurements made on several dielectric tapes under consideration by a superconducting power transmission line project as well as on epoxies which appear mechanically suitable as low-tempetature bushing material. The measurement technique and instrumentation are described. View full abstract»

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  • Ageing of Insulatiog Materials and Equipment Insulation in Service and in Tests

    Publication Year: 1977 , Page(s): 55 - 60
    Cited by:  Papers (4)
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    After a discussion of the concepts of ageing of insulations and of the endurance of insulating materials, the importance of verifying the relevance of ageing to insulation failure in equipment is pointed out. Information regarding frequency distributions of service stresses and of the stress dependence of insulation strength is also required. After a discussion of ageing versus changes of property, problems of evaluating the endurance of insulating materials, functional testing of insulation systems, and of the acceptance testing of equipment insulation are briefly reviewed. The paper concludes by recommending certain areas which should be studied in order to improve rational, consistent and economic evaluation methods. View full abstract»

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  • Thermal Ageing of Cellulose Paper Insulation

    Publication Year: 1977 , Page(s): 61 - 66
    Cited by:  Papers (16)
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    Results are presented of investigations into the thermal ageing behavior of cellulose paper insulation in which tests have been carried out between 100C and 160C on well-dried samples of cellulose paper contained in sealed glass vessels in an atmosphere of initially dry nitrogen gas. The degree of ageing has been assessed by measuring the time rate of decrease of several physical and physico-chemical characteristics of the cellulose paper, e.g. burst strength, degree of polymerization etc., and conclusions were drawn concerning their relative sensitivities to the state of ageing of the test sample. In addition to these measurements, the rates of production of the main gaseous decomposition products have also been determined. View full abstract»

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  • Application of the Equalized Ageing Process Method on Thermal Endurance Testing of Polyhydantoin Film

    Publication Year: 1977 , Page(s): 67 - 74
    Cited by:  Papers (5)
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    Thermal endurance test results on polyhydantoin film are presented, performed both in the conventional atmospheric conditions and in the conditions fulfilling the requirements for the equalized ageing process. The basic principle of the Equalized Ageing Process method (EAP) for thermal endurance testing of solid electrical insulating materials is to make the ageing process at the test temperature equal to that at the service temperature, by changing the test atmosphere appropriately. In an equalized ageing process all the chemical ageing reactions are accelerated equally. Test results in the EAP conditions are in very good agreement with the EAP theory, showing the same acceleration factor for chemical ageing reactions and for deterioration of physical properties. In the tests performed in the conventional atmosphere there was no common acceleration factor to be found for the chemical reactions and for deterioration rates of the physical properties. Consequently only those thermal endurance test results obtained using the EAP method can be a basis for calculating the useful life of the material at the service temperature. View full abstract»

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  • On the use of Polyethylene Insulation in the Manufacture of Submarine Cables

    Publication Year: 1977 , Page(s): 75 - 79
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    In the manufacturing process of a submarine coaxial cable, a multitrough water cooling system is used to avoid formation of voids and to strengthen the gripping force between the insulation polyethylene and the metallic center conductor. In submarine coaxial cable systems, the standards for dielectric properties of the insulation, polyethylene, are very strict. The adverse effect of small amounts of water in the polyethylene can not be neglected. In the cable manufacturing process quench cooling is favorable to the decrease of the water content in polyethylene. On the other hand, gradual cooling is better to avoid formation of voids. To find the optimum manufacturing process under these two conflicting conditions, computor simulations of the diffusion mechanism of water in polyethylene and the void forming mechanism have been made using available experimental data. View full abstract»

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  • A 25 Factorial Experiment Investigating the Effects of Operating Conditions on Cable Insulation Life

    Publication Year: 1977 , Page(s): 80 - 85
    Cited by:  Papers (2)
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    The method and interim results of a three-year laboratory investigation are reported on the effects of five in-service environmental factors. These factors include 1) presence or absence of water, 2) ambient air temperature, 4) presence or absence of daily voltage impulses, and 5) presence or absence of currend loading. A 5 kV UniShield R cable was used in the experiment. Through an analysis of variance, the operating conditions that significantly influence cable life are being assessed. View full abstract»

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  • On the Behavior of Liquid/Solid Insulations at Very Low Frequency

    Publication Year: 1977 , Page(s): 86 - 89
    Cited by:  Papers (2)
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    The apparent increase of the capacitance of solid/liquid insulations measured at very low frequency under low voltage (~l v), is mainly produced by the appearance of polarization layers (ions are impeded at the interfaces) provided that adequate conditions are fulfilled for the densities and mobilities of ions, and for the frequency and amplitude of the applied voltage. Thus, the insulation behaves approximately as a capacitance (the capacitance of the polarization layer, which may reach several ¿F/cm2, a value frequently encountered in electrochemistry) in series with the resistance of the dielectric (which shunts the geometrical capacitance measured at high frequency). View full abstract»

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  • Influence of the Fines on the Dielectric and Tensile Breakdown of Oil-Impregnated Paper

    Publication Year: 1977 , Page(s): 90 - 96
    Cited by:  Papers (3)
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    The ideal composition of fibers for insulating paper has been clarified by investigating the influence of the shape of fines on dielectric and tensile breakdown of oil-impregnated Kraft paper for oil filled (OF) cable at 105N/M oil. Furthermore, the pulp refining methods for producing such insulating paper have been investigated. View full abstract»

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  • Correction

    Publication Year: 1977 , Page(s): 96
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Aims & Scope

This Transactions ceased production in 1993. The current retitled publication is  IEEE Transactions on Dielectrics and Electrical Insulation.

Full Aims & Scope