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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 1 • Date February 2009

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  • IEEE Transactions on Dielectrics and Electrical Insulation - Table of contents

    Publication Year: 2009 , Page(s): c1
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    Freely Available from IEEE
  • IEEE Dielectrics and Electrical Insulation Society - Committee

    Publication Year: 2009 , Page(s): c2
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    Freely Available from IEEE
  • Water absorption in a glass-mica-epoxy composite - [I: Influence on Electrical Properties]

    Publication Year: 2009 , Page(s): 1 - 10
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB) |  | HTML iconHTML  

    Water absorption in an epoxy composite used for insulation of stator bars in large generators is investigated in order to study both diffusion kinetics and effects on dielectric properties. Water absorption can be described by the superposition of two Fickian mechanisms, the first occurring within epoxy and the other at interfaces between epoxy and fillers. A large decrease of breakdown strength versus water uptake is observed. It points to the large deleterious effect of water on insulation reliability. Dielectric spectroscopy is performed under various conditions of water impregnation, electric field and temperature. A very large increase of permittivity and losses is recorded in the presence of water, especially at low frequency. At power frequency, dielectric properties do not show a non-linearity when the field is increased up to service values. At very low frequency, a decrease of losses when the field is increased is observed. It is due to the Garton effect. Most of results show that the wet material behaves as a low frequency dispersion system (LFD). View full abstract»

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  • Water absorption in a glass-mica-epoxy composite [II: field distribution and diagnostic in a stator bar geometry]

    Publication Year: 2009 , Page(s): 11 - 16
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB) |  | HTML iconHTML  

    In this paper, the water concentration profile within the insulation of a stator bar in the presence of a water leak is calculated by resolving the Fick's equation. The temperature strongly activates diffusion processes, but the shapes of concentration profiles remain similar. From the measured dielectric properties versus water content, an electrical model is developed in order to calculate the field and potential distribution within the insulation. The field is reduced in wet zones due to the high local permittivity and conductivity compared to dry zones. This effect is favorable since the breakdown field is lowered in wet zones. On the other hand, the field in dry zones is reinforced, but the value attained remains lower than the short-term breakdown strength. This explains why stator bars in the presence of waters leaks may survive for long times, in spite of high local water concentrations in excess of 1%. The high sensitivity of dielectric properties at low frequency to the presence of water suggests non-destructive methods to detect wet bars in a real power generator. View full abstract»

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  • The application of recurrence plot in DC tracking test of gamma-ray irradiated polycarbonate

    Publication Year: 2009 , Page(s): 17 - 23
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3724 KB) |  | HTML iconHTML  

    Irradiation effects on tracking resistance of polymer insulation materials should be investigated due to the increasing usage in radiation-prone environments. This paper presents a study on dc tracking resistance of gamma-ray irradiated polycarbonate mixed with polyethylene by use of IEC 60112 method. The samples were irradiated in air up to 100 kGy and 1000 kGy with a dosage rate of 10 kGy/h using a 60Co gamma source. Because the data of tracking resistance obtained from the tracking test has a wide variation, discharge current in the test is considered as a main factor to estimate the tracking resistance. A recurrence plot analysis of discharge current has been made to evaluate the tracking resistance more consistently. Obtained results showed that after gamma-ray irradiation, the tracking resistance was improved compared with that of the unirradiated sample. The tracking resistance showed an increasing tendency from 0 kGy to 100 kGy but a decreasing tendency from 100 kGy to 1000 kGy. There was a threshold value for the tracking resistance around 100 kGy, which was related to the reaction of cross-linking and degradation. The topological structures of the recurrence plots with the irradiated samples were different from that of the unirradiated one. There were bigger white space segments, which indicated that there were high amplitude transients in the discharge currents of unirradiated sample. The recurrence point density increased from 100 kGy to 1000 kGy, which suggested that the discharge process of the total dose at 1000 kGy was more intensive than that at 100 kGy. The irradiation effects on the tracking resistance can be visually identified by the recurrence plot. View full abstract»

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  • Effective area of thin guarded electrode in determining of permittivity and volume resistivity

    Publication Year: 2009 , Page(s): 24 - 31
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    Effective area of guarded electrode is always larger than its geometrical area as a result of fringing effect. In most standards concerning permittivity and volume resistivity measurements, an increase in the effective fringing is assumed as a half of the width of the gap between the guarded electrode and the guard electrode (then the factor B = 1). In some standards, the increase calculated from Amey relation, is assumed to be smaller (B < 1). The Amey relation is exact only for sample permittivity epsivrarrinfin . It is correct to apply the relation to calculate the volume resistivity, but it is incorrect to use it to calculate the permittivity of a sample. In this paper, a proper relation for the factor B has been derived analytically for thin electrodes made usually by thin film technology. The factor B can be used to calculate the permittivity of samples with arbitrary value of epsiv. Appropriate changes into the standard IEC 60250 and into other standards concerning permittivity measurements are proposed. View full abstract»

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  • Influence of ground and corona currents on dielectric behavior of small air gaps

    Publication Year: 2009 , Page(s): 32 - 41
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (409 KB) |  | HTML iconHTML  

    This paper investigates the influence of grounding on the field distribution and on the dielectric behavior of small rod-plate and rod-rod air gaps. This effect can be attributed to the grounding of one electrode. In the different arrangements with one electrode grounded or with the electrodes symmetrically charged the experimental results of the corona and breakdown are recorded and compared to the simulation results of the field distribution. It is resulted that the grounding influences significantly the electric field distribution, the dc corona and the dc breakdown. The field is less inhomogeneous in grounded rod - plate air gaps and in rod-rod air gaps with symmetrically charged electrodes, and consequently the values of the corona onset and the breakdown voltage are higher. In longer air gaps the corona current influences the field distribution and consequently the dc breakdown. The effect of grounding on the breakdown is weakened when the dc polarity of the voltage is negative, otherwise it is enhanced. In air gaps with lengths > 3 cm (negative dc polarity) or >8 cm (positive dc polarity) it is overlapped by the effect of the corona current. Relations between the field strength, the corona current, the corona onset and the breakdown voltage arise. The principle of action-reaction is valid. View full abstract»

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  • Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

    Publication Year: 2009 , Page(s): 42 - 51
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (318 KB) |  | HTML iconHTML  

    To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six kinds of non-standard lightning impulse waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Then, the dielectric breakdown voltage iquest time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gaps and partly the coneshaped insulating spacers that represent insulation elements of GIS for six kinds of nonstandard lightning impulse waveforms. In this paper, the resultant breakdown voltages were evaluated in terms of the overvoltage duration, which led to their formulation in a unified way. On the basis of these insulation characteristics and their unified formulation, the paper investigated a method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. When the constructed algorithm was applied to five examples of representative two type waveforms in the lightning surge time region, they were converted into standard lightning impulse waveforms with crest values reduced by 20% to 34%, suggesting potentiality for reduction of lightning impulse insulation specifications of GIS. View full abstract»

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  • Erosion resistance and mechanical properties of silicone nanocomposite insulation

    Publication Year: 2009 , Page(s): 52 - 59
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (307 KB) |  | HTML iconHTML  

    The results of erosion resistance, tensile strength, elongation at break, hardness, and thermal stability measurements are presented for silicone nanocomposites prepared using various nano and micro silica and alumina fillers in a two-part silicone rubber (SiR) matrix. The fillers are used to improve the erosion resistance of SiR, which is necessary for outdoor insulation housing applications. Good dispersion of the fillers is achieved using Triton/sup TM/, a common surfactant. An optimal surfactant concentration imparts good erosion resistance to the nanocomposites in laser heating tests without adverse effects, but excess surfactant has a negative impact on the mechanical properties of the silicone. Thermal gravimetric analysis demonstrated that nano fumed silica imparts better heat resistance to silicone than natural nano silica or nano alumina fillers. Fourier transform infrared spectroscopy analysis of the nanofillers indicated a significantly higher concentration of silanol groups in the nano fumed silica filler than in micro silica. The influence of the increased number of silanol groups on the erosion resistance of the nanocomposites and their mechanical properties is discussed. View full abstract»

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  • Electromagnetic wave radiated from an insulating spacer in gas insulated switchgear with partial discharge detection

    Publication Year: 2009 , Page(s): 60 - 68
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (775 KB) |  | HTML iconHTML  

    As a means of diagnosing partial discharge (PD) signals propagate inside a gas insulated switchgear (GIS), a study for the leakage of electromagnetic waves (EM-waves) emitted from the insulating spacer was implemented. The EM-waves leaking out from the solid insulator have the resonance frequencies depend on the spacing between adjacent bolts in the direction of the flange circumference, because the leakage portion is the equivalent of a slot antenna. In this paper, using an electromagnetic analysis model which has a simulated spacer on a concentrically-shaped GIS tank, the output characteristics of the EM-waves that leaked out from the slit were analyzed under various conditions such as the spacing between adjacent bolts, the width of the spacer, the dielectric constant of the spacer and the form of the flange. Also the actual measurement by the experimental equipment used to simulate the model was implemented for comparison with the analytical results. Consequently, the optimal specifications of the sensor and the measurement method used to achieve highly-sensitive detection for practical use were summarized and proposed as well as evaluating the effectiveness of the electromagnetic analysis model adopted in this paper. View full abstract»

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  • Bird streamer caused flashover in EHV transmission line

    Publication Year: 2009 , Page(s): 69 - 76
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (527 KB) |  | HTML iconHTML  

    The bird-streamer caused failures have become one of the major causes of transmission line outages. It is more common and widespread than generally believed, and greatly threatens the reliability of transmission lines. The laboratory study of such failures mechanism is seldom reported especially for long gaps such as 500 kV insulators. Presented in this paper are the results of long air gaps bird streamer flashover experiments conducted on 500 kV and 220 kV transmission line insulators. The experimental results demonstrated that bird-streamer caused surface flashover can happen in 500 kV insulators, however space flashover, because the bird streamer will split into different jets under high electric field cannot short circuit the long air gaps. The high risk areas of flashover for 220 kV and 500 kV insulators were defined in this paper: an elliptical area for 220 kV I string insulator and a symmetrical area beside the central line for 500 kV V string insulator. The influence of some main factors on flashover processes is also elucidated, such as volume, conductivity and viscosity of the streamer, and the insulator type and configuration. The paper has significant value in understanding the bird caused failure mechanisms and designing remedies. View full abstract»

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  • Modeling of epoxy resin spacers for the 1 MV DC gas insulated line of ITER neutral beam injector system

    Publication Year: 2009 , Page(s): 77 - 87
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (271 KB) |  | HTML iconHTML  

    The spacers for the gas insulated transmission line for the ITER neutral beam injector will be designed to withstand the operating voltage of 1 MV dc. Electric charging processes of the spacer surface are then expected to play an important role in the final electric field distribution. Aim of the paper is to investigate the effects of the different conductivity properties of the SF6-Spacer insulating structures on the surface charge set-up, and to identify a procedure to minimize this charge. Based on the most updated literature, the paper presents and discusses the results of two newly developed simulation tools: the first consisting of a quasi-static non linear model for epoxy spacer based on finite element method code ANSYStrade, the other consisting of a spacer profile optimization package, whose kernel is based on a genetic algorithm. The numerical tools have been applied to post and disk spacer models of the gas insulated line; in particular, the optimization package has been used on the disk spacer, and the comparison between un-optimized and optimized spacer in terms of electric charge accumulated are presented and discussed. View full abstract»

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  • Flashover prevention on high-altitude HVAC transmission line insulator strings

    Publication Year: 2009 , Page(s): 88 - 98
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (331 KB) |  | HTML iconHTML  

    Numerical analysis, on-site measurements, and laboratory experiments are used in this paper to analyze and solve the flashover problems of 330 kV AC high altitudes transmission line middle phase glass suspension insulator strings. A sub-model approach based on a finite element method (FEM) applied in calculating the potential and electric field distribution along the insulator strings under clean and dry conditions. Using this approach, three dimensional electrostatic models (taking into account the grading rings, subconductors, tower framework, and yoke plates) are set up and investigated. On-site and laboratory measurements were also carried out to make a comparison. A relatively good agreement was obtained among the calculated, the on-site, and the laboratory measured results, which demonstrated that insulator disk nearest to the high-voltage end is required to withstand relatively high voltage according to the standard in China; in addition, the insufficient dry arc distance of the insulator strings is also proposed. Subsequently, the long insulator-string flashover tests under dry, wet, and artificial contaminated (ESDD=0.05 mg/cm/2, NSDD=0.3 mg/cm/2) conditions, considering the middle (flashover) and side phase (never flashover), respectively, are carried out to validate the proposed insufficient dry arc distance and discuss the measures for solving the flashovers. From the effective, convenient and economical standpoint for the reconstruction of the flashover lines, lowering the grading rings' position and adding a unit of insulator are considered to lengthen the dry arc distance of the middle-phase insulator string in the tests. The experimental results are compared and discussed, and it has been concluded that adding a unit of insulator is an effective and economical way to solve the flashover problems. The methods for analyzing the flashover problems are effective and can be used for other voltage-level transmission lines. View full abstract»

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  • Signal analysis methods to distinguish tracking process using time-frequency analysis

    Publication Year: 2009 , Page(s): 99 - 106
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB) |  | HTML iconHTML  

    This paper proposes a method to distinguish the tracking process only in terms of voltage waveforms. Tracking is simulated using the IEC (International Electrotechnical Commission) 60112 method. The tracking process is observed in 5 stages - static state, discharge inception, discharge in progress, carbon formation, and tracking breakdown. The measured voltage waveforms are analyzed by two signal processes. The two kinds of signal processing are: improved time-frequency and time-energy analysis. The tracking process can be distinguished by using the improved time-frequency analysis visually by stages. It can also be distinguished by using average and standard deviation for the results of the time-energy analysis. Particularly, probability distribution for the result of the time-energy analysis appears a regular pattern in tracking process by stages. View full abstract»

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  • Microstructure based evaluation of field aged and new porcelain suspension insulators

    Publication Year: 2009 , Page(s): 107 - 115
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1883 KB) |  | HTML iconHTML  

    Porcelain suspension insulators that were in service for up to 38 years on 115-500 kV transmission lines were evaluated for electrical and mechanical properties. The microstructure of the porcelain and cement was examined using analytical techniques like scanning electron microscopy and x-ray diffraction. It has been shown that insulators that performed well in service for many years had microstructural details that were notably different from those that exhibited significant reduction in residual electrical strength and punctured in the laboratory test. This information has been utilized to rank new insulators made presently that were obtained from the users. View full abstract»

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  • A basic study on the effect of voltage stress on a water droplet on a silicone rubber surface

    Publication Year: 2009 , Page(s): 116 - 122
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (551 KB) |  | HTML iconHTML  

    Observations and analyses have been conducted on the behavior of water droplets deposited on the surface of polymer insulators. As an index to characterize the repellency of water droplets on the polymer surface, the contact angle was measured for different situations. Experiments were conducted to see the behavior of water droplets of different volumes and their size distribution on silicone rubber. Electric field strength calculation was performed to analyze the effect on water droplets. Finally, effects of the Maxwell stress and the Coulomb's force were compared, to conclude that, even if there is some true charge on the water droplet, the Maxwell stress is predominant. View full abstract»

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  • Study on AC pollution flashover performance of composite insulators at high altitude sites of 2800-4500 m

    Publication Year: 2009 , Page(s): 123 - 132
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB) |  | HTML iconHTML  

    The newly constructed Qinghai-Tibet Railway connecting Golumd and Lhasa is the highest railway in the world, which is located on the hinterland of Qinghai- Tibet Plateau with the average altitude of above 4000 m. Therefore, the external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. In contrast to many test investigations in the artificial climate chamber, there are few ones at the high altitude sites of 3000 m and above. In the paper, the AC artificial pollution tests of four types of composite insulators are carried out at three high altitude sites of 2820 m, 3575 m and 4484 m along the Qinghai-Tibet Railway. The test results show that the AC pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The pollution flashover voltages will decrease with the increase of air pressure but increase with the decreases of ambient temperature. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.32 and the exponent characterizing the influence of non-soluble deposit density is 0.12 to 0.16, the influence of non-soluble deposit density cannot be neglected. The exponent characterizing the influence of air pressure is 0.507 to 0.587. The exponent characterizing the influence of ambient temperature is about 0.20. Considering the combined influence of the air pressure and ambient temperature, the AC flashover voltage of the polluted composite insulators will decrease by 4.0% to 6.4% for the altitude increased per 1000 m. View full abstract»

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  • Aging effect on leakage current flow in wooden poles

    Publication Year: 2009 , Page(s): 133 - 138
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (250 KB) |  | HTML iconHTML  

    Insulation degradation leading to leakage current flow through high voltage insulators could result in catastrophic failures such as pole fires and damages to nearby equipment. This paper examines the leakage current distribution originating from the high voltage conductor to various locations through the wooden pole of various age profiles. The specimens that are investigated in this paper range from a new sample to an aged pole sample of more than 20 years in service. The main results show that the aging effect on the wooden pole has great effect on the wood resistance. The decaying of the wood reduces the wood resistance and thus increases the leakage current. Thermal images showing heating of the king bolt due to leakage currents are also presented. View full abstract»

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  • Recurrent plot analysis of leakage current for monitoring outdoor insulator performance

    Publication Year: 2009 , Page(s): 139 - 146
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (522 KB) |  | HTML iconHTML  

    Outdoor insulators are widely accepted in power industry to maintain electrical insulation ranging from distribution to transmission lines. Such increasing development leads to a lack of appropriate diagnostic tools for assessing the performance of insulator in service, particularly in contaminated conditions. In order to monitor operating performance of contaminated outdoor insulators, a recurrent plot technique is proposed to analyze the leakage current passing through the insulator surface. Contamination tests were conducted in a laboratory by employing heavy salt fog with the deposition of non-soluble contamination. The leakage current was decomposed into different frequency components by using a wavelet transform technique. The temporal sequence of the extracted component was extended to m-dimensional phase space by using a phase-space reconstructed method. The recurrent plot is obtained to show that the topological structure of the high-frequency components is prominent to identify non-linear properties of discharge activities. Based on the analysis of the high-frequency components, the quantitative indicators of recurrent plot are obtained to reflect the underlying mechanism of flashover process. The results obtained indicate that the recurrent plot technique gives visual recurrent patterns of discharge activities for monitoring outdoor insulator performance. The dynamic behaviors on the insulator surface are graphically illustrated on the rectangular block structures with higher density of points. The structure changes indicate the switches of discharge states during the flashover process. View full abstract»

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  • Skin effect and dielectric loss models of power cables

    Publication Year: 2009 , Page(s): 147 - 154
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (899 KB) |  | HTML iconHTML  

    In power electronics applications, power cables spread paths of conducted disturbances throughout the system. This paper proposes a high frequency modeling method for power cables that takes into account phenomena which appear when the switching frequency of the static converter increases, such as skin effects, proximity effects and dielectric losses. The proposed power cable models are obtained by the series association of n identical RLCG basic cells. The skin and proximity effects are represented as the impedance of an R-L ladder and the dielectric losses as the admittance of an R-C ladder. The proposed method was successfully applied to a three-wire unshielded cable and extended to a four-wire shielded cable. View full abstract»

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  • Severe degradation of the conductor screen of service and laboratory aged medium voltage XLPE insulated cables

    Publication Year: 2009 , Page(s): 155 - 161
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (802 KB) |  | HTML iconHTML  

    The main purpose of this paper is to show the strong correlation between corrosion of the metallic aluminum conductor and the formation of interconnected cracks / voids in the conductor screen, creating initiation sites for vented water trees in service aged medium voltage XLPE cables. The results show that porous structures in the conductor screen previously reported for laboratory aged insulation systems, also develop in the conductor screen in service aged medium voltage XLPE cables. These structures can bridge the screen and serve as path for contaminants and corrosion products from the aluminum conductor and initiate water trees. A prerequisite for the formation of such structures is the presence of liquid water at the interface between the conductor and conductor screen causing corrosion. The initiation site of such structures has been identified, and is likely caused by environmental stress cracking (ESC). Initiation sites were determined in all cables, but porous structures in the conductor screen were only observed in the cable suffered from service failure, where liquid water had entered the cable conductor between the strands. Severe degradation of the XLPE insulation was observed at the initiation sites for water trees growing from these structures. View full abstract»

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  • Correlation between tan δ diagnostic measurements and breakdown performance at VLF for MV XLPE cables

    Publication Year: 2009 , Page(s): 162 - 170
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (653 KB) |  | HTML iconHTML  

    The main contribution of this paper is to investigate the correlation between tan delta diagnostic measurements at 0.1 Hz (Very Low Frequency-VLF) and VLF breakdown performance for medium voltage (MV) cable samples through a laboratory test program. The cable samples used are a set of 15 kV, Cross-linked Polyethylene (XLPE), unjacketed cables removed from the field, the same service area, and having experienced similar operating conditions for almost four decades. The test program includes tan delta measurements at different voltage levels and a subsequent VLF extended step-withstand test. The VLF step test allows the evaluation of risk of failure during VLF tan delta testing and assessment of the ultimate performance of the cables. The tan delta diagnostic measurements are represented by the tan delta value and tip-up, which are considered the classical metrics. However, the paper also suggests the use of a new additional diagnostic feature that takes into account the scatter in the tan delta measurements for a particular test voltage level. View full abstract»

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  • A versatile method to study electrical treeing in polymeric materials

    Publication Year: 2009 , Page(s): 171 - 178
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (769 KB) |  | HTML iconHTML  

    Electrical treeing in high voltage cable insulation has been studied widely as it is one of the major breakdown mechanisms for solid dielectrics subjected to high electrical stresses. The most frequently experimental set-up used to study electrical treeing is utilizing needles to achieve a high divergent field to promote the initiation of electrical trees. In this paper a new type of electrode configuration is described, which will be beneficial when examining electrical treeing in terms of both the capability to follow the course of events in real time and the small amount of insulation material is needed. This new electrode configuration makes use of a thin tungsten wire as electrode to obtain the high divergent electrical stress needed to initiate electrical trees. Multiple electrical trees are at times formed at different points along the wire during the testing, this indicates that the field are homogenous along the wire. This allows for determining the tree initiation field and the rate of tree growth. It is also shown that this electrode configuration is able to distinguish the increased electrical tree inception obtained by the addition of voltage stabilizers. View full abstract»

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  • Electrical treeing characteristics in XLPE power cable insulation in frequency range between 20 and 500 Hz

    Publication Year: 2009 , Page(s): 179 - 188
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (381 KB) |  | HTML iconHTML  

    Electrical treeing is one of the main reasons for long term degradation of polymeric materials used in high voltage AC applications. In this paper we report on an investigation of electrical tree growth characteristics in XLPE samples from a commercial XLPE power cable. Electrical trees have been grown over a frequency range from 20 Hz to 500 Hz and images of trees were taken using CCD camera without interrupting the application of voltage. The fractal dimension of electric tree is obtained using a simple box-counting technique. Contrary to our expectation it has been found that the fractal dimension prior to the breakdown shows no significant change when frequency of the applied voltage increases. Instead, the frequency accelerates tree growth rate and reduces the time to breakdown. A new approach for investigating the frequency effect on trees has been devised. In addition to looking into the fractal analysis of tree as a whole, regions of growth are being sectioned to reveal differences in terms of growth rate, accumulated damage and fractal dimension. View full abstract»

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  • Suppression of electrical tree initiation in LDPE by additives of polycyclic compound

    Publication Year: 2009 , Page(s): 189 - 198
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (519 KB) |  | HTML iconHTML  

    Tree initiation voltages (TIVs) for LDPEs with additives of the polycyclic compounds were measured to investigate the fundamental role of the compound in the suppression of tree initiation. Five types of polycyclic compounds were used as additives: naphthalene (Np), anthracene (An), 9,10-dibromoanthracene (Br-An), tetracene (Te), and pentacene (Pn). The experimental results indicated that TIV depends on the typed of the compound: TIV for LDPE with "An" is about 3.5 times higher than that for LDPE without an additive; TIVs for "Np", "Te" and "Pn" are not significantly increased. The mechanism for the dependence of TIV on the type of the compound was discussed based on the following experimental investigations: the fundamental electric characteristics for the test materials (conduction current, permittivity and tan delta); the spectra for UV absorption of the test materials due to the excitation of the compound and the spectra for the luminescence emitted from the test materials due to the deexcitation; the shape of the precipitates of the additives in LDPE; and the surface feature for the test materials by AFM. The measurements and observations suggested that the highest TIV for LDPE with "An" is accomplished mainly by two factors: the relaxation of the electric field due to the semi-conductive precipitates of plate-shape crystal, and the shallower depth of micro-spaces located at the interface between LDPE and the electrode. Although the excitation of additive increases TIV, it is not a significant factor in the dependence of TIV, because the spectra indicated that the excitation occurs even in the materials with additive, which is ineffective to the increase in TIV. View full abstract»

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Aims & Scope

IEEE Transactions on Dielectrics and Electrical Insulation contains topics concerned with dielectric phenomena and measurements with development and characterization of gaseous, vacuum, liquid and solid electrical insulating materials and systems.

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Editor-in-Chief
Reuben Hackam