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Showing papers in "IEEE Transactions on Electrical Insulation in 1982"


Journal ArticleDOI
TL;DR: The discovery and development of manmade polymer materials dates from the pioneering works of Goodyear (vulcanized rubber) and Hyatt (celluloid plastics) in the mid-nienteenth century, and to Baekeland (Phenol-formaldehyde resins) at the beginning of this century, the remarkable growth of the synthetic fiber, rubber, and plastics industries followed the preparative achievements of the I.C.I.
Abstract: Whilst the discovery and development of manmade polymer materials dates from the pioneering works of Goodyear (vulcanized rubber) and Hyatt (celluloid plastics) in the mid-nienteenth century, and to Baekeland (Phenol-formaldehyde resins) at the beginning of this century, the remarkable growth of the synthetic fiber, rubber and plastics industries followed the preparative achievements of the I.C.I. group in Cheshire (polyethylene), Carothers at Du Pont, Wilmington (linear polyesters and nylons) and the German chemists (polyvinyl halides) in the 1930's, and the U.S. Government Synthetic Rubber Program during World War II. The ability to vary chemical structure and composition (e.g. for copolymers) and physical structure (by fillers, plasticizers, thermal and mechanical treatments, processing methods) made it possible to create materials which could be tailor-made for a particular application. Thus the industries grew to the dominant positions they hold today.

340 citations


Journal ArticleDOI
Steven A. Boggs1, G. C. Stone1
TL;DR: In this article, the theoretical sensitivity of conventional partial discharge detectors is compared with that obtained from ultra wideband (UWB) (up to l GHz) detection systems, and the comparison indicates that for relatively lossfree distributed systems, such as SF6 insulated bus, the UWB system is up to two orders of magnitude more sensitive.
Abstract: The theoretical sensitivity of conventional partial discharge detectors is compared with that obtained from ultra wideband (UWB) (up to l GHz) detection systems. The comparison indicates that for relatively lossfree distributed systems, such as SF6 insulated bus, the UWB system is up to two orders of magnitude more sensitive. UWB detection also embodies additional advantages such as facilitating the location of discharge sites and the rejection of external electrical noise. For discharge detection in plastic-insulated cables, true UWB detection is not practical because of frequency-dependent attenuation effects, although certain gains in sensitivity can be achieved with a detector bandwidth of up to 10 MHz.

184 citations


Journal ArticleDOI
TL;DR: In this article, it has been shown that it is possible to extend the validity of the Townsend breakdown criterion for evaluating the breakdown voltages in the complete pd range in which Paschen curves are available.
Abstract: It has been shown that it is possible to extend the validity of the Townsend breakdown criterion for evaluating the breakdown voltages in the complete pd range in which Paschen curves are available. Evaluation of the breakdown voltages for air (pd=0.0133 to 1400 kPa · cm), N2(pd=0.0313 to 1400 kPa · cm) and SF6 (pd=0.3000 to 1200 kPa · cm) has been done and in most cases the computed values are accurate to ±3% of the measured values. The computations show that it is also possible to estimate the secondary ionization coefficient ? in the pd ranges mentioned above.

160 citations


Journal ArticleDOI
P. P. Wong1, Eric O Forster1
TL;DR: In this paper, the electrical breakdown process in highly purified and degassed liquid hydrocarbons has been studied, using high speed schlieren photography as well as photomultipliers and an optical multichannel analyzer.
Abstract: The electrical breakdown process in highly purified and degassed liquid hydrocarbons has been studied, using high speed schlieren photography as well as photomultipliers and an optical multichannel analyzer It was shown that the breakdown process appears to be initiated primarily on the cathode surface The ensuing formation of tree-like streamers was found to be associated with light emission This light appears to be of the same spectral composition as that given off during actual breakdown Spectral analysis of the emitted light indicated the presence of atomic and molecular hydrogen, carbon molecules of the type C2 and C3, as well as metal atoms emanating from the electrode surface The significance of these findings is discussed in detail

65 citations


Journal ArticleDOI
K. P. Brand1
TL;DR: In this paper, it was shown that these properties are related to two basic molecular characteristics, the polarizability and the ionization potential, and the relations found are helpful in determining general trends and estimating unknown data.
Abstract: For practical application of an insulating gas three different properties, i.e. the dielectric strength, the boiling point, and the toxicity are important. Based on semi-quantitative physical arguments and confirmed by known data of 41 gases, it is shown that these properties are related to two basic molecular characteristics, the polarizability ? and the ionization potential ?i. The relations found are helpful in determining general trends and estimating unknown data.

54 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of pressure on dc breakdown voltage of contaminated porcelain insulators and glass models was investigated in the range of 13 to 100 kPa, and it was shown that flashover voltage decreases nonlinearly with lowering of pressure.
Abstract: The effect of pressure on dc breakdown voltage of contaminated porcelain insulators and glass models was investigated in the range of 13 to 100 kPa. The study revealed that flashover voltage decreases nonlinearly with lowering of pressure. Arc characteristics under different pressure conditions were studied and the theoretical basis of low pressure flashover is discussed.

47 citations


Journal ArticleDOI
TL;DR: In this paper, two dielectric relaxation peaks, the crystalline and the primary relaxations, were observed in the temperature-dielectric loss curves in isotactic polypropylene.
Abstract: Two dielectric relaxation peaks, the crystalline and the primary relaxations, were observed in the temperature-dielectric loss curves in isotactic polypropylene. Among them the primary relaxation s was studied in detail using different kinds of polypropylene films and their films purified with acetone. It was found that s-relaxation consists of two peaks, denoted s1 and s2, being consistent with the dynamic mechanical characteristics. The lower temperature peak s1 is assigned to the amorphous phase, which is rich in atactic chains, and the upper temperature peak s2 is ascribed to an antioxidant contained in the amorphous phase which is rich in isotactic chains. The antioxidant also causes an increase in dielectric loss in the higher temperature region. The extraction of impurities from polypropylene films with acetone reduces the magnitude of the primary relaxation peaks.

40 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of compressive and tensile stresses on the dielectric strength of bi-stretched polyethylene terephthalate (PET) and epoxy glass cloth (FRP, G-10) are reported at room temperature.
Abstract: Organic materials to be used for the electrical insulation of superconducting magnet coilsin large fusion reactors must withstand electrical stresses under high mechanical loads, extreme temperatures, and intense nuclear radiation. In this paper, measurements at room temperature are reported on the effects of mechanical compressive and tensile stresses on the dielectric strengths of bi-stretched polyethylene terephthalate (PET) and epoxy glass cloth (FRP, G-10) which are widely used for the insulation of superconducting magnet coils. For PET, the breakdown strength increases with increase of compressive stress in the region of elastic deformation but decreases in the region of inelastic deformation. The value of compressive stress showing maximum dielectric strength is independent of film thickness and is approximately 100 MPa, smaller than the stress appearing in large fusion reactors. In the case of FRP, the behavior of breakdown characteristics under compressive stress is nearly the same as that of PET but the relationship between characteristics of electrical breakdown strength and mechanical properties of FRP isnotclear because it is a composite of two materials: epoxy resin and glass filler. The effect of tensile stress on the dielectric strength is small for PET, but significant for FRP.

35 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of frequency on the growth of water trees in polyethylene has been investigated using the water needle test, and an accelerating effect was observed up to a maximum between 4 and 8 kHz with both NaCl solution and deionized water.
Abstract: The effect of frequency on the growth of water trees in polyethylene has been investigated using the water needle test. An accelerating effect was observed up to a maximum between 4 and 8 kHz with both NaCl solution and deionized water. This phenomenon cannot be ascribed to a frequency dependence of the electrical behavior of the trees. It results from the mechanical properties of the polymer itself and can be interpreted by analogy with environmental stress cracking. The frequency dependence of the growth rate appears to be a consequence of the existence of a mechanical absorption peak in polyethylene located at about 30 kHz at room temperature.

32 citations


Journal ArticleDOI
TL;DR: The gaseous degradation products of low density polyethylene exposed to corona discharges were investigated in this paper, where temperature and applied voltage were varied independently in order to determine the effect of each on the chemical processes involved in the degradation.
Abstract: The gaseous degradation products of low density polyethylene exposed to corona discharges were investigated. Temperature and applied voltage were varied independently in order to determine the effect of each on the chemical processes involved in the degradation. Based upon statistical analysis of the results, temperature was found to have an anomalous effect on the accumulation of organic gas products in that increased temperature resulted in lesser amounts of these gases being found.

29 citations


Journal ArticleDOI
TL;DR: In this article, a method has been developed to characterize the resistance of polymers to erosion by surface discharges, and a method is proposed to use the test in conjunction with outdoor test station data to obtain an estimate of service life.
Abstract: A method has been developed to characterize the resistance of polymers to erosion by surface discharges. It was found possible to produce surface discharges on wet, contaminated surfaces without the usual disturbing influences of metal electrodes and wetting agents. Instrumentation was devised to monitor continuously the electrical behavior of the test specimens. The test yields a quantitative erosion rate in mg/C which is characteristic of the material and test conditions used. In addition, the electrical measurements permit the detection of long-term changes in the surface properties. A method is proposed to use the test in conjunction with outdoor test station data to obtain an estimate of service life.

Journal ArticleDOI
TL;DR: In this article, a simple analysis showed that the increase in resistance to electrical treeing by additives is associated with this field-dependent conductivity, and a model for the behavior of the additives which leads to the lowering of electrical stress at sites of high and divergent electrical stresses is given.
Abstract: On the basis of the experimental observation that the conductivity of acetophenone-doped polyethylene is field dependent over a range of applied electric stresses, a simple analysis shows that the increase in resistance to electrical treeing by additives is associated with this field-dependent conductivity. The additives can be considered as weak electrolytes. The rate of their dissociation into positive and negative charge carriers which causes an increase in conductivity is field dependent. A model for the behavior of the additives which leads to the lowering of the electrical stress at sites of high and divergent electrical stresses is given. Presently available experimental results are in good agreement with our proposed theory. Other factors affecting this mechanism are also discussed.

Journal ArticleDOI
TL;DR: In this article, the breakdown behavior of a 50 mm negative rodplane gap is investigated for N2, air, CO2 and their binary mixtures with SF6 for pressures of up to 0.5 MPa using rod of 0.794 mm radius and impulse voltages of 2/50
Abstract: Breakdown behavior of a 50 mm negative rod-plane gap is investigated for N2, air, CO2 and their binary mixtures with SF6 for pressures of up to 0.5 MPa using rod of 0.794 mm radius and impulse voltages of 2/50 ?sec. It is shown that at high gas pressures, mixtures containing low SF6 content can have breakdown voltages lower than the corresponding values in pure gases. Furthermore, the results indicate that SF6-CO2 mixtures perform somewhat better than SF6-N2 and SF6-air mixtures and can have breakdown voltages slightly higher than those for pure SF6. On the contrary, SF6-air and SF6-N2 mixtures have breakdown voltage levels which are always below their respective values for SF6. Furthermore, it is shown that when gas pressure is equal or higher than 0.1 MPa, leader-type corona exists in almost all of these mixtures. Also when the gas pressure and SF6 content of the mixture are high, leader discharge extends into the gap in a stepped manner. Detailed results of these investigations are described and discussed in this paper.

Journal ArticleDOI
TL;DR: In this paper, the complex relative permittivity of polyethylene/mica composites has been measured in the frequency range 10-2 to 107 Hz, as a function of mica content and prior sample conditioning.
Abstract: The complex relative permittivity ?*(f) of polyethylene/mica composites has been measured in the frequency range 10-2 to 107 Hz, as a function of mica content ?2 and prior sample conditioning. ?*(f) was found to display two main features: ?'-?' ?and K'' vary as fn-1 with 0.64?n?0.83 for all ?2, on account of the intrinsic dispersive properties of the mica. In addition, K'' displays a broad peak centered in the audio frequency range, associated with ?Maxwell-Wagner-Sillars? losses due to absorbed water. Finally, the high frequency permittivity K'? is compared with various ?mixture formulae in the literature; Sillars' theory is found to fit experimental data well, even at high ?2 values.

Journal ArticleDOI
TL;DR: In this paper, the effects of thermal properties and morphology of cross-linked polyethylene on its impulse voltage breakdown stress, as determined by the use of miniature cables, were investigated.
Abstract: This paper describes fundamental studies into the effects of (1) the thermal properties, and (2) the morphology of cross-linked polyethylene on its impulse voltage breakdown stress, as determined by the use of miniature cables. Nine grades of high pressure polyethylene, characterized by molecular structure, are used in the studies. The degree of crystallinity of XLPE is found to be closely related to impulse voltage breakdown stress, which increases when crystallinity is increased. Therefore, the fact that impulse voltage breakdown stress decreases with temperature can be associated with a decrease in crystallinity. Likewise the thickness of the amorphous zone is found to increase with temperature, although the crystal thickness has changed onlyslightly. From this point of view, the amorphous zone appears to play an important role in the occurrence of impulse breakdown in that the breakdown seems to originate from the amorphous zone.

Journal ArticleDOI
TL;DR: A review of the elementary processes which play a role in the initiation and propagation of electric breakdown processes in liquids is given in this paper, which is essentially limited to pure, non-polar liquids subjected to step-impulse voltages and to voltages which vary slowly in time (dc, line-frequency ac).
Abstract: A review is given of the elementary processes which play a role in the initiation and the propagation of electric breakdown processes in liquids. The discussion is essentially limited to pure, non-polar liquids subjected to step-impulse voltages and to voltages which vary slowly in time (dc, line-frequency ac). The topics treated include: electrode processes, ionization in the liquid phase, bubble formation, and evolution of the breakdown phenomenon.

Journal ArticleDOI
TL;DR: In this article, the dielectric breakdwon strength (DBS) of PET and FRP under compressive stress at 77 K shows similar variations to those obtained with ac at room temperature: the DBS increases at first, reaches a maximum value, and falls thereafter.
Abstract: The electric insulators for superconducting magnet coils to be used in a large fusion reactor are subjected to large compressive and tensile stresses to a maximum level of about 400 MPa, and these stresses should pose a significant electrical insulating problem in practice. In this paper, dc and ac dielectric breakdown characteristics of PET and FRP under mechanical stress at liquid nitrogen (LN2) temperature are presented as part of a comprehensive study for electrical insulating design of superconducting magnet coils to be used in a large fusion reactor. The results presented are complementary to those already reported for ac at room temperature. The dielectric breakdwon strength (DBS) of PET and FRP under compressive stress at 77 K shows similar variations to those obtained with ac at room temperature: the DBS increases at first, reaches a maximum value, and falls thereafter. The maximum DBS is little influenced by the temperature variation, but the compressive stress showing the maximum DBS depends strongly on the temperature regardless of voltage sources used. Under tensile stress the DBS of PET and FRP at 77 K is higher than at room temperature at a given tensile stress.

Journal ArticleDOI
TL;DR: In this paper, thermally stimulated discharge (TSD) was used in low density polyethylene (LDPE) double needle samples, and electronic space charge densities of 2.7×10-3 Ccm-3 have been shown to exist in shallow (~3?m) regions surrounding the needle tips following ac stressing at a maximum field of 1.2×108 Vm-1.
Abstract: Electron injection into polymers from field stress concentration sites is now generally accepted as important for the initiation of electrical trees, although very few published studieshave so far provided direct evidence for this. By means of the thermally stimulated discharge (TSD) technique in low density polyethylene (LDPE) double needle samples, electronic space charge densities of 2.7×10-3 Ccm-3 have been shown to exist in shallow (~3 ?m) regions surrounding the needle tips following ac stressing at a maximum field of 1.2×108 Vm-1. The present TSD results agree well with ?conventional? TSD data (planar samples, dc polarization) in the literature.

Journal ArticleDOI
TL;DR: In this paper, an attempt has been made to find a relationship between the characteristic voltages obtained using the single-needle and doubleneedle tests, and a conversion factor has been derived which is in good agreement with experiment.
Abstract: An attempt has been made to find a relationship between the characteristic voltages obtained using the single-needle and doubleneedle tests. A conversion factor has been derived which is in good agreement with experiment.

Journal ArticleDOI
TL;DR: In this article, it is proposed that the formation of a disturbance region is due to the coulombic repulsion of local homocharges which in turn causes a decrease in local density and hence a decrease of refractive index.
Abstract: The shadowgraphic image reflects only those regions of disturbance occurring in a dielectric liquid, which differ in refractive index from their surroundings. The time required for the onset of a prebreakdown disturbance after the application of a step voltage, and the rate of growth of the disturbance depend strongly on the viscosity (or the temperature) of the liquid. The refractive index is lower inside the disturbance region than outside. The variation of the external current is consistent with the temporal change of the disturbance. It is proposed that the formation of a disturbance region is due to the coulombic repulsion of local homocharges which in turn causes a decrease in local density and hence a decrease in refractive index. At highfields the anode injects holes to form positive ions and the cathode injects electrons, and theelectric conduction is filamentary. The electric breakdown in condensed materials (liquids and solids) involves double injection and the creation of low density regions to enable the charge-carrier multiplication processes to take place. Thus the breakdown strength is governed by the parameters which control the conditions for such prebreakdown phenomena to arise.

Journal ArticleDOI
D. W. Tong1
TL;DR: In this paper, a diffuse, monoenergetic electron beam of variable energy is used to measure space charge profiles in thin polyethylene terephthalate (PET) films.
Abstract: A diffuse, monoenergetic electron beam of variable energy is used to measure space charge profiles in thin polyethylene terephthalate (PET) films. A quantitative model of the method used for the profile calculations is presented. Results are given of measured charge profiles set up both by electron beam deposition and by voltage poling. The method is shown to have a spatial resolution of about 0.5 ?m and a minimum detectable charge density of about 0. 5×102 C/m3 for PET. Inherent experimental problems are identified and potential uses of the method are discussed.


Journal ArticleDOI
TL;DR: In this paper, a general method for the solution of ac low frequency electric fields in insulating systems is proposed, based on decoupling Maxwell's equations, and their solution can beimplemented analytically or numerically.
Abstract: A general method for the solution of ac low frequency electric fields in insulating systems is proposed. The method is based on decoupling Maxwell's equations, and their solution can beimplemented analytically or numerically. The finite difference numerical method is easily implemented to solve the field in polluted insulators.

Journal ArticleDOI
TL;DR: In this article, a brief review of the charge simulation technique used for the calculation of high voltageelectrostatic fields, and its application to a typical transmission line disc insulator section under pollution-free conditions, is presented.
Abstract: A brief review of the charge simulation technique used for the calculation of high voltageelectrostatic fields, and its application to a typical transmission line disc insulator sectionunder pollution-free conditions, is presented. The use of ring and line charges has been found to be quite adequate for the modeling of the field distribution in and around the insulator with an accuracy in the representation of electrode potentials well within 1% of the maximum potential difference. The discrepancy in representing the inter-dielectric interface conditions is usually a maximum of about 9% but may be as large as 17% for the tangential electric field.

Journal ArticleDOI
TL;DR: In this paper, a simple formula is developed to predict the sparking potentials of SF6 and SF6-gas mixture in uniform and non-uniform fields, and the formula has been shown to be valid over a very wide range from 1 to 1800 kPa·cm of pressure and electrode gap separation for mixtures containing 5 to 100% SF6.
Abstract: A simple formula is developed to predict the sparking potentials of SF6 and SF6-gas mixture in uniform and non-uniform fields. The formula has been shown to be valid over a very wide range from 1 to 1800 kPa·cm of pressure and electrode gap separation for mixtures containing 5 to 100% SF6. The calculated values are found to be in good agreement with the previously reported measurements in the literature. The formula should aid design engineers in estimating electrode-spacings and clearances in power apparatus and systems.

Journal ArticleDOI
TL;DR: In this paper, a study of polyethylene terephthalate (PET) and polypropylene (PP) treated by corona discharge for a short time is presented, where different techniques of analysis such as inverse chromatography, infrared spectroscopy, loss tangent and electric strength were used.
Abstract: A study of polyethylene terephthalate (PET) and polypropylene (PP) treated by corona discharge for a short time is presented. Different techniques of analysis such as inverse chromatography, infrared spectroscopy, loss tangent and electric strength were used. Working at 50 Hz with a gap of 2 mm and different gases, the analysis of the polymer after treatment has shown that a limit in the transformation of the surface may be considered. Thus a critical time is defined between a pure transformation and a degradation. This latter phase is also studied with a cross linked polyethylene (XLPE). The infrared analysis and electric strength measurements have shown the role played by the relative humidity present in air.

Journal ArticleDOI
TL;DR: In this paper, the electric field configuration has been analyzed numerically by the charge simulation method near a contact point where two media having surface or volume conductivity meet an electrode, resulting in a uniform field throughout both media for very low resistivity.
Abstract: The electric field configuration has been analyzed numerically by the charge simulation method near a contact point where two media having surface or volume conductivity meet an electrode. Surface conduction with uniform surface resistivity moderates the field singularity, resulting in a uniform field throughout both media for very low resistivity. On the other hand, volume conduction magnifies the field singularity if only one medium has conductivity. For these capacitive-resistive fields, it appears impossible to derive a simple analytical expression of field strength such as can be derived for purely capacitive cases.

Journal ArticleDOI
TL;DR: In this paper, the effect of prestressing on the breakdown strength and time lag of low-density polyethylene films subjected to square pulses of 100 ns width was analyzed and the breakdown mechanism was discussed on the basis of an avalanche-stream-transition in the gaseous breakdown theories.
Abstract: This paper describes the effect of prestressing on the breakdown strength and time lag of lowdensity polyethylene films subjected to square pulses of 100 ns width. When prestress and impulse fields are opposite in polarity, the 50% breakdown strength Eb decreases from 4.9 to 3.4 MV/cm as the prestressing field is increased from 0 to 4.6 MV/cm. When prestress and impulse fields have the same polarity, Eb increases to 5.4 MV/cm as the prestress is increased to 4.1 MV/cm. The dc break-down strength is 5.8 MV/cm. The formative time lag tf decreases with increasing applied field. The value of tf is insensitive to the level of prestress within a given mode. The mode of opposite prestress yields considerably larger values of tf than the other two modesof no and same prestress, and at relatively low applied fields. The apparent electron mobility calculated from tf increases from 2.2×10-2 to 2.4×10-1 cm2/Vs as the total (prestress +pulse) applied field is changed from 3.0 to 6.0 MV/cm. The results are attributed to a modification of the field intensity near the electrodes due to space charge accumulation during the period of prestressing. The breakdown mechanism is discussed on the basis of an avalanche-streamertransition in the gaseous breakdown theories.

Journal ArticleDOI
TL;DR: In this paper, the authors used an optimization technique employing a modified objective function which minimizes not only the accumulated squared potential error but also the tangential electric field along the conducting surface.
Abstract: Numerical field solutions employing the charge simulation method (CSM) have been obtained for the rod-plane gap geometry which is of considerable importance in High Voltage Engineering research It is shown that conventional techniques do not necessarily lead to accurate solutions in the entire interelectrode space A method is suggested which uses an optimization technique employing a modified objective function which minimizes not only the accumulated squared potential error but also the tangential electric field along the conducting surface This method yields solutions with good accuracy in the entire interelectrode space

Journal ArticleDOI
TL;DR: In this article, an ageing test was performed on two high-voltage motor insulation systems using three principal ageing stresses: temperature, electric field, and mechanical stress, with the goal of an ageing process identical with that at service conditions.
Abstract: An ageing test was performed on two high-voltage motor insulation systems using three principal ageing stresses: temperature, electric field, and mechanical stress. An equal acceleration of each stress was used with the goal of an ageing process identical with that at service conditions. For the determination of the true acceleration factor a parallel ?ageing? test at service conditions was run, up to so long testing times that changes in characteristic properties (flexural modulus, tan?, and capacitance) could be determined. Humidity tests and high-voltage withstand tests were also performed after each ageing cycle. The observed acceleration factor for both systems was lower than predicted. In one of the systems the changes in characteristic properties were measurable and of the same type at both test conditions, so that the test acceleration could be evaluated reliably. Both systems show good class F performance connected with appropriately defined severe service conditions.