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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 1 • Date February 2012

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  • IEEE Transactions on Dielectrics and Electrical Insulation [Front cover]

    Page(s): c1
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  • Executive committee

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  • Application of contact analysis on evaluation of breakdown strength and PD inception field strength of solid-solid interfaces

    Page(s): 1 - 7
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    Interfaces between solid insulating materials are generally weak regions in electrical insulation systems, particularly if the electrical stress is applied in parallel direction. This paper presents a theoretical mechanical model for estimating average size of air-filled voids at the interface as a function of surface roughness and contact pressure. It is argued that the interfacial breakdown strength (BDS) is governed by the discharge inception stress (Ev) of the void with the most likely estimated dimension. The estimated values of the breakdown strength and partial discharge inception electric field strength (PDIE) were compared with the results from measurements using XLPE specimens with interfaces energized in longitudinal direction. The measured ratio of increase of breakdown strength was found to be in good agreement with the estimated breakdown values of the most likely interface's void. Additionally, it was found out that the air pressure inside voids was not affected by applied contact pressure. The estimated PDIE values was found to be in agreement with the measured values, in the case of rough surfaces, but not for smooth surfaces. The results indicate that the mechanical contact approach using the motif description of surface roughness may improve the understanding of the factors influencing the PDIE of electrically stressed interfaces. View full abstract»

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  • Study of partial discharge radiated electromagnetic wave propagation characteristics in an actual 154 kV model GIS

    Page(s): 8 - 17
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    A method to detect partial discharge (PD) is considered effective for gas insulated switchgear (GIS) insulation diagnostics. In this paper, for a 154 kV model GIS, the influence of the enclosure diameter on PD propagation characteristics was initially investigated using model GIS by varying the enclosure size. Secondly, an experiment was conducted for metallic particles placed in different locations as a source of PD (particle adhering to the center conductor or free metallic particle). Thirdly, an actual PD experiment was conducted in an Lshaped form to study the influence of GIS shape on PD-radiated electromagnetic (EM) waves. In addition, in order to study the experimental results in detail, a simulation using the FD-TD method was conducted for comparison with these experimental results. Following the experiment, the larger the enclosure diameter, the greater the measured amplitude of PD having occurred around the center conductor. In addition, it emerged that, where the particle was close to the center conductor, EM waves propagating due to PD were less likely to be damped compared with the case where particles were placed on the bottom of the enclosure. Furthermore, following the investigation of the propagation characteristics in the L-shaped form, it emerged that, while a high frequency component of frequency exceeding that of the TEM wave component was reflected at the L-shaped part, the TEM wave component passed through almost unaffected by the latter. The propagation of the TEM mode component could be also found via FD-TD analysis. View full abstract»

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  • A methodology for identification and localization of partial discharge sources using optical sensors

    Page(s): 18 - 28
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    The present work represents a methodology to detect the location of single as well as multiple Partial Discharge (PD) sources by optical method and to investigate the performance of optical sensors for this purpose. An experimental setup has been arranged in the laboratory for generation of PDs, optical sensing and analysis of the recorded signals obtained from multiple optical sensors. The analysis results prove the effectiveness of the methodology using optical sensors to find whether PD is occurring at single location or multiple locations. For identification of PD locations pattern recognition technique has been utilized by considering the received optical energy as a feature. For feature selection and classification two techniques have been evaluated, viz. Gaussian Mixture Model (GMM) and Support Vector Machine (SVM), and both have shown promising performance. SVM in regression mode was used for identification of unknown PD location/locations. In this case average accuracy obtained was 92.6% when PD is occurring at one location and 80.1% when PD is occurring at two locations. The obtained results indicate that, the proposed methodology can be used to locate partial discharges in high voltage equipment where the optical signals due to discharges find a path to get radiated towards the outer surface. View full abstract»

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  • Partial discharge recognition through an analysis of SF6 decomposition products part 1: decomposition characteristics of SF6 under four different partial discharges

    Page(s): 29 - 36
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    Partial discharge (PD) is usually aroused before the failure of gas insulated switchgear (GIS) caused by defects, which results in the decomposition of the SF6 used as insulating gas. Analyzing SF6 decomposition products can aid in PD detection. Before recognizing PD types by analyzing SF6 decomposition products, the decomposition characteristics of SF6 under different types of PD should be investigated first. In this paper, a gas chamber and four typical types of artificial defects were designed to simulate the SF6 decomposition phenomenon under PD in GIS. A gas chromatography system was established to detect SF6 decomposition products. By selecting the chromatographic column, SF6 decomposition products were successfully separated and their concentrations were measured. Numerous SF6 decomposition experiments under four kinds of PD generated by four kinds of artificial defects were carried out and the SF6 decomposition products produced by each experiment were detected. The decomposition characteristics of SF6 under the four defects were different in terms of decomposition amount, generation rate, and concentration ratio, among others. It is feasible to recognize the type of PD by analyzing SF6 decomposition products. View full abstract»

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  • Partial discharge recognition through an analysis of SF6 decomposition products part 2: feature extraction and decision tree-based pattern recognition

    Page(s): 37 - 44
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    The decomposition characteristics of the SF6 under the different kinds of partial discharges (PD) should be understood first when recognizing PD by analyzing SF6 decomposition products in gas insulated switchgear (GIS). Moreover, the characteristic quantities used for recognition must be found. In this paper, the concentration and concentration ratio of SF6 decomposition products were each selected as characteristic quantities. Fuzzy c-means clustering algorithm was adopted to assess the performance of the two types of characteristic quantities, which was based on the data of SF6 decomposition products under the four kinds of PD in Part 1. Concentration ratio had better performance than concentration as a characteristic quantity in PD recognition. The concentration ratio method for PD recognition was established based on the decision tree theory, in which the three concentration ratios, namely c(SOF2)/c(SO2F2), c(CF4)/c(CO2), and c(SOF2 +SO2F2)/c(CO2+CF4), were used as characteristic quantities. The physical significance of the three concentration ratios was also analyzed. Finally, the concentration ratio method was applied to test the performance of PD recognition. The method has a good performance and can successfully recognize different kinds of PD. View full abstract»

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  • Life tests on twisted pairs in presence of partial discharges: influence of the voltage waveform

    Page(s): 45 - 52
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    The stator windings of electrical motors fed by means of inverter drives are subjected to switching voltages that constitute a heavy electrical stress for the winding insulation systems. Such stress together with the uneven distribution of potential along the windings and the possible presence of voltage peaks, due to resonance and reflection phenomena, often leads to premature failure of Type I winding insulation. In this study the electrical aging of enamelled insulating wires in presence of PDs has been investigated considering the applied voltage waveform as the core of the degradation processes together with the voltage amplitude. The experimental activity consisted in life test campaigns on twisted pair specimens. The specimens have been stressed applying five voltage waveforms until the total breakdown; some of the waveforms are designed in order to reproduce the output of a PWM drive. The times to breakdown relevant to different voltage amplitudes have been collected and lifetime plots for each voltage waveform have been computed and traced. It has been demonstrated that life time values are greatly affected by the particular shape of the test voltage. Furthermore, the obtainable life curves relevant to the pulsed waveform simulating the PWM drive conditions have to be traced by means of two straight lines having different slopes. View full abstract»

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  • Experimental evaluation of using the surge PD test as a predictive maintenance tool for monitoring turn insulation quality in random wound AC motor stator windings

    Page(s): 53 - 60
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    Turn insulation degradation is one of the major root causes of stator insulation failure leading to motor breakdown. The surge test is the only test available for testing the integrity of turn insulation; however, it is a high voltage pass/fail test that provides an indication only if an arc is instigated between the turns of weakened turn insulation, and therefore does not provide information regarding remaining lifetime. The surge PD test measures the partial discharge (PD) activity under surge excitation, and is used to date for assuring that voltage source PWM inverter-fed motors (IEC 60034-18-41 type I) are PDfree. In this paper, the potential of using the surge PD test as a predictive maintenance tool for turn insulation quality assessment is evaluated. Under the expectation that increasing PD activity in the voids formed by insulation degradation may be detectable before turn insulation failure, the test is performed periodically under accelerated thermal degradation on 6 windings. It is shown that change in the PD inception voltage under the surge PD test can be clearly observed before any other insulation test indicator. The results suggest that the surge PD test can be used for monitoring the condition of turn insulation for providing an early indication of stator insulation problems without the risk of puncturing turn insulation. View full abstract»

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  • Contribution of humidity to the evolution of slot partial discharges

    Page(s): 61 - 75
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    The impact of humidity on the slot partial discharge (PD) process was evaluated in a laboratory experiment conducted in a climatic chamber under constant humidity and temperature. Two stator bars, subjected to slot PDs at two temperatures (28°C and 85°C), were aged at twice their nominal phase-to-ground voltage (16 kV) under three absolute humidity levels (5 g/m3, 9 g/3 and 13 g/3). The phase resolved partial discharge (PRPD) patterns were monitored during short aging sequences and visual observations of the surfaces were made at the beginning and end of each aging sequence. Observation confirms that humidity has a significant impact on the discharge phenomenon but other parameters, such as surface condition and temperature, affected the discharge process just as much. This paper presents the way slot PD activity evolves and affects the related PRPD pattern under different conditions of humidity, temperature and surface degradation. View full abstract»

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  • Influence of nano-scaled zirconia particles on the electrical properties of polymer insulating materials

    Page(s): 76 - 82
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    In the present work the influence of nano-scaled zirconia particles with different structures on the structural and electrical properties of polyurethane (PU) insulating coatings was investigated. PU matrix insulating coatings containing non-doped and 4 mole % yttrium doped nano-scaled zirconia with average particle size between 12 and 13 nm were prepared by wet chemical methods. High resolution transmission electron microscopy analysis of thermally cured composites showed that the nano dispersed zirconia particles were uniformly distributed within matrix. Incorporation of 5 vol. % nanoparticles into the PU matrix resulted in a slight increase of the micro hardness and elastic modulus. The effect of zirconia filling (non-doped and doped) on the electrical breakdown strength was not observed. But, a strong influence of the nanoparticle addition on the partial discharge stability was detected. Partial discharge breakdown time for non-filled PU matrix was 2.5 h, for PU filled with non-doped zirconia 65 h and for PU filled with yttrium doped zirconia >; 100 h, respectively. The additional benefit of doped zirconia may be explained by its different electronic structure and polarisation behaviour. View full abstract»

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  • Synthesis and dielectric behavior of nano-scale barium titanate

    Page(s): 83 - 90
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    In this study, an effort has been made to synthesize nano-scale barium titanate powder by sol-gel and hydrothermal methods. Characterization of the synthesized Barium Titanate is conducted by using X-ray diffraction for crystallite size, Transmission Electron Microscopy for particle size and scanning electron microscopy for surface morphology. It is observed that the powders prepared by Sol-gel and hydrothermal routes have almost similar average crystallite size of 34 ± 2 nm. Electrical properties such as dielectric constant, dielectric dissipation factor and electrical resistivity have also been measured. Hydrothermal process has enabled the synthesis of material with higher dielectric constant of 4000 compared to the Sol-gel route value of 1600. The dielectric dissipation factor is measured and found to be below 0.3 over a wide range of frequencies for powders generated using both processes. View full abstract»

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  • Tracking and erosion of silicone rubber nanocomposites under DC voltages of both polarities

    Page(s): 91 - 98
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    In order to improve the tracking and erosion performance of outdoor polymeric silicone rubber (SR) insulators used in HV power transmission lines, micron sized inorganic fillers are usually added to the base SR matrix. In addition, insulators used in high voltage dc transmission lines are designed to have increased creepage distance to mitigate the tracking and erosion problems. ASTM D2303 standard gives a procedure for finding the tracking and erosion resistance of outdoor polymeric insulator weathershed material samples under laboratory conditions for ac voltages. In this paper, inclined plane (IP) tracking and erosion tests similar to ASTM D2303 were conducted under both positive and negative dc voltages for silicone rubber samples filled with micron and nano sized particles to understand the phenomena occurring during such tests. Micron sized Alumina Trihydrate (ATH) and nano sized alumina fillers were added to silicone rubber matrix to improve the resistance to tracking and erosion. The leakage current during the tests and the eroded mass at the end of the tests were monitored. Scanning Electron Microscopy (SEM) and Energy dispersive Xray (EDX) studies were conducted to understand the filler dispersion and the changes in surface morphology in both nanocomposite and microcomposite samples. The results suggest that nanocomposites performed better than microcomposites even for a small filler loading (4%) for both positive and negative dc stresses. It was also seen that the tracking and erosion performance of silicone rubber is better under negative dc as compared to positive dc voltage. EDX studies showed migration of different ions onto the surface of the sample during the IP test under positive dc which has led to an inferior performance as compared to the performance under negative dc. View full abstract»

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  • Inverter surge resistant enameled wire with nanocomposite insulating material

    Page(s): 99 - 106
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    An inverter surge resistant enameled wire was developed with innovative organic/inorganic nanocomposite insulating material by dispersing an inorganic material at a nanometer level. It successfully achieved satisfactory levels for both partial discharge resistance and coating film flexibility and strength. This product can maintain a voltage endurance of more than 1000 times as high as those offered by general enameled wires even after mechanical stress is applied. This paper describes how the product can dramatically improve the reliability of magnet wires and open the way for performance warrant of inverter-fed motors in actual operation up to a surge voltage around 1.5 kVp. View full abstract»

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  • Anomalous behaviour of the dielectric spectroscopy response of nanocomposites

    Page(s): 107 - 117
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    A study on the dielectric spectroscopy of epoxy-based nanocomposites filled with different types of particles, such as Al2O3, AlN, MgO, SiO2 and BN, is presented. The surface of the nanoparticles was modified with a silane coupling agent, in order to make them compatible with the organic host and create a system with homogeneously dispersed filler material. Morphological characterizations of individual particles and fabricated composites were performed by means of transmission and scanning electron microscopy. The present research addresses an analysis of the complex permittivity. The relative permittivity of nanocomposites shows an unusual behaviour. Introduction of a low percentage of high permittivity filler results in a decrease of the permittivity of the bulk polymer material. We propose a qualitative explanation for the reduction of the relative permittivity, compared to the reference samples. The interface layer of surface modified particles plays a more important role than the nature of the particles themselves. The immobilization caused by the surface treatment of the nanoparticles seems to be the main factor determining the relative permittivity of the composites with fillgrade below 5 wt.%. The imaginary part of the complex permittivity, which represents the dielectric losses in the system, does not change significantly with addition of nanofiller up to 5 wt.%. View full abstract»

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  • Corona resistance of epoxy nanocomposites: experimental results and modeling

    Page(s): 118 - 125
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    Epoxy composites with micro, nano and micro + nano silica fillers have been evaluated for their resistance to corona using point plane electrodes. The experiments were conducted for 500 h and the surface erosion was measured after every 100 h using a surface profilometer. The results show significant improvement in corona resistance of micro+nanofilled samples and nanofilled samples when compared with the microfilled samples and unfilled materials respectively. The results emphasize the importance of good filler dispersion. A model to map the degradation path in the filled and unfilled samples was developed using Dijkstra's shortest path algorithm. Reasonable agreement between the length of degradation path and the corona resistance in samples containing both micro + nanofillers has been demonstrated. View full abstract»

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  • Analysis of space charge formation in LDPE in the presence of crosslinking byproducts

    Page(s): 126 - 133
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    Cross-linking byproducts are suspected to be the main contributing factor in space charge formation observed in XLPE. To investigate the mechanism behind this phenomenon, low density polyethylene was soaked into three main crosslinking byproducts, acetophenone, α-methylstyrene and cumyl alcohol, and space charge measurements were performed using the Pulse Electroacoustic technique (PEA). It has been found that soaking LDPE in cumyl alcohol introduces more charges into the system, with homocharges and heterocharges accumulating within the sample compared to the additive free sample. In contrast, α-methylstyrene and acetophenone reduce the amount of accumulated charges. In terms of charge decay, all three byproducts enhance the decay process in the insulator. Further investigations were conducted in conditions where two byproducts are present in a sample. The results shows that acetophenone is a dominant byproduct in determining the charge density patter built up during the charging process, whilst the rate of charge decay is observed to be high in the presence of α-methylstyrene in the sample. View full abstract»

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  • Measurements of electrical potential of constant charge objects

    Page(s): 134 - 139
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    Direct and compensating methods of potential measurements on constant charge objects are discussed in the paper. It is generally known, that in case of potential measurements using direct method the total capacitance of the investigated object is enlarged by additional capacitance introduced by the meter and the corresponding voltage value is lower in comparison to that in a non disturbed state. Discussion of the compensation method of potential measurements on constant charge objects in the context of validity of Gauss law leads to the conclusion that the measured values of potential will be higher and the total capacitance of the object will be smaller in comparison to the state non disturbed by the compensating head (probe). Cases of high and low capacitance objects were considered. The effect of capacitance reduction was illustrated by the "potential measurements of the Q-constant object, surrounded by the compensating electrode" experiment. Conclusions coming from the discussion were confirmed experimentally. View full abstract»

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  • Effect of voltage reversal on space charge and transient field in LDPE films under temperature gradient

    Page(s): 140 - 149
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    Voltage reversal will strongly affect the stability of cable in service, especially under temperature gradient due to the temperature rise of the cable. In this paper, the results of space charge profiles and field distortions in low density polyethylene (LDPE) films after dc pre-stress of 50 kV/mm for 2 h under temperature gradient and then during different voltage reverse polarities or during different voltage reverse periods were presented. The test results show that the charge accumulation and field distortion are different under different voltage polarities due to the dependence of charge injection on electrode materials. In this work, under the Al / SC (Semiconductive) electrode system with a temperature difference of 40°C, the maximal transient field occurs near the low temperature Al electrode when polarity varies from negative to positive while near the high temperature SC electrode when polarity varies from positive to negative. In addition, the faster the voltage reversal at room temperature the higher the maximal transient field, but the faster the voltage reversal the lower the maximal transient field under temperature gradient. Moreover, the maximal field appears during voltage inversion at room temperature while appears at pre-stress under temperature gradient. View full abstract»

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  • Characteristics and mechanisms of surface charge accumulation on a cone-type insulator under dc voltage

    Page(s): 150 - 155
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    In order to study the phenomenon of surface charge accumulation on cone-type insulators, a surface charge measuring system is established, based on the electrostatic probe method. The surface potential distributions on a cone-type insulator are measured and the charge distributions are calculated based on the 3D field calculation by the surface charge method. The characteristics of charge distributions are compared under different voltage durations and voltage amplitudes. The results show that the charge accumulation comes to a steady state after 120 min. A threshold voltage effect is observed that charges seldom accumulate unless the applied voltage reaches a certain magnitude. The mechanisms of charge accumulation are discussed. The surface conduction and volume conduction do not seem to dominate the charge accumulation on the insulator. Partial discharges in gas may be the main sources of surface charges. View full abstract»

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  • Accelerated aging effects of mineral and vegetable transformer oils on medium voltage power transformers

    Page(s): 156 - 161
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    The usage of vegetable oil for power transformer insulation has increased, compared to mineral oil, for its better environmental characteristics. However, although the temperature rise depending on load difference and the relationship between hottest spot temperature and life time depending on long-term operation for mineral oil immersed transformer has been studied, there is being established for vegetable oil immersed transformer. Therefore, the MV power transformers either filled with conventional mineral oil or with vegetable oil are thermally aged and the transformer oils are sampled regularly. With these samples, the chemical, mechanical and electrical characteristics of the two oils are investigated by the aging time. According to our experiment, the degradation rate of vegetable oil can be compared to that of mineral oil. View full abstract»

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  • Mechanisms behind positive streamers and their distinct propagation modes in transformer oil

    Page(s): 162 - 174
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    Comprehensive modeling and analysis is presented for the charge generation, recombination, attachment, and transport of positive ions, negative ions, and electrons in transformer oil between a positive high voltage sharp needle electrode and a large spherical ground electrode. Case studies show that a key mechanism in streamer development is field ionization, which is the direct ionization of molecules due to action of the electric field. Due to the high mobility electrons, which are about 1 × 105 times more mobile than the positive ions, the newly generated electrons quickly exit the high field ionization zone towards the anode leading to the development of a net positive space charge peak which subsequently creates an electric field enhancement in the oil. The process is driven by the applied high voltage creating temporally dynamic space charge and electric field distributions that develop an ionizing wave that drives streamer development. The pre-breakdown modeling and analysis elucidates the development of different streamer modes in transformer oil. In particular, the analysis focuses on mechanisms driving filamentary fast mode streamers discussed in the literature. The results demonstrate that streamer modes arise in transformer oil due to the ionization of different families of hydrocarbon molecules (i.e., aromatic, naphthenic, and paraffinic) at increasing electric field levels (or applied voltages). Ionization of the low concentration aromatic molecules in transformer oil, that generally have lower ionization energies than naphthenic/paraffinic molecules, leads to the propagation of streamers with velocities on the order of 1 km/s. As the applied voltage is increased, the ionization of the main hydrocarbon molecules in transformer oil, high concentration naphthenic/paraffinic molecules, dominates producing high electric field levels and space charge at the streamer tip. This results in the propagation of a very fast streamer with veloci- ies on the order of 10 km/s. Furthermore, these streamers have protrusion spacing in the approximate range of 20-100 μm in ~36 ns like those of electrohydrodynamic instability of charged jets that may be the origin of streamer branching. A preliminary model based on earlier electrohydrodynamic stability analysis is presented that predicts protrusion spacing in the approximate range of 7-30 μm with growth rate 2.5-5 μs. View full abstract»

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  • Effects of Irgamet 30 as additive in transformer oil

    Page(s): 175 - 180
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    This study was designed to examine the impact of a recently identified undeclared additive Irgamet® 30 in transformer oils. Therefore, several laboratory studies were performed. First, the stability of Irgamet® 39, a well-known metal passivator was tested. It was clear that Irgamet® 39 protected copper from corrosive sulfur compounds such as dibenzyl-disulfide (DBDS). As the structure of Irgamet® 30 is comparable to the one of Irgamet® 39, the stability/degradability, impact on oxidation stability of the oil and corrosive sulfur compounds were tested on lab-scale. The stability was determined by performing a heating test based on IEC61125C. Irgamet® 30 decreased to undetectable within 24h. The presence of a Cu coil could accelerate this decrease. The impact on the oxidation stability was tested by subjecting the oils to the IEC61125C oxidation stability test, once without any pretreatment, secondly after IX-resin treatment (recommended by IEC60296 Ed.4) and finally after IX-resin treatment and readdition of the initial Irgamet 30 concentration. It could be concluded that the IX-resin treatment removed the triazole-like oxidation inhibitors present in the oil, such as Irgamet® 30 and some other (natural) inhibitors. As the oxidation stability was not fully recovered after readdition of the initial Irgamet® 30 content this could mean that not only Irgamet® 30 was removed during IX-resin treatment but also that some other (natural) inhibitors were present. In a final laboratory study the impact of Irgamet® 30 on corrosive sulfur was examined. The oils were subjected to the IEC62535 before and after IX-resin treatment. It seemed that Irgamet® 30 did not protect the oil from DBDS. Therefore, the results of this study indicated that Irgamet® 30 di- not effectively mitigate corrosive sulfur, however, it did enhance oxidation stability. View full abstract»

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  • Analysis methods of sulfide and sulfoxide compounds in mineral insulating oil for diagnosis on electrostatic charging of power transformers

    Page(s): 181 - 187
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    Analysis methods of sulfide and sulfoxide compounds in mineral insulating oil are developed to diagnose an electrostatic charging of a power transformer due to oil circulation. When sulfonium ions are generated from sulfide compounds via sulfoxide compounds, they tend to increase an electrostatic charging tendency (ECT) in the oil, which causes the electrostatic charging of a power transformer. Selective analysis methods for sulfide and sulfoxide compounds are developed by combining solid extractions with a gas chromatography because it is difficult to detect sulfonium ions directly. Sulfide compounds are selectively extracted from oils by palladium chloride-impregnated silica gel while sulfoxide compounds are extracted by silica gels. The effect of sulfide on the dielectric dissipation factor (DDF), which relates to an ECT, of commercial oil is investigated by removing sulfide compounds with palladium chloride-impregnated silica gel. The DDF of untreated oil increases at the beginning of heating with air while changes in the DDF are minimal for treated oils. View full abstract»

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  • Quantitative analysis ageing status of natural ester-paper insulation and mineral oil-paper insulation by polarization/depolarization current

    Page(s): 188 - 199
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    Polarization and Depolarization Current (PDC) technique is an effective tool to assess the condition of oil-paper insulation system in power transformers. So far the PDC behaviors of mineral oil-paper insulation have been widely investigated. However, with the increasing number of transformer choosing natural ester as its insulation oil, it is important to investigate the PDC characteristics of natural ester-paper insulation to see whether the PDC technique can also be used to assess the condition of new insulation system using natural ester in transformers accurately. In this research, natural esterpaper insulation sample and mineral oil-paper insulation sample were subjected to thermally accelerated ageing experiment at 110°C for 120 days. The PDC characteristics of natural ester-paper insulation sample and mineral oil-paper insulation sample were compared over the ageing process. A new method for assessing the ageing condition of the oil-paper insulation in terms of the depolarization charge quantity was proposed. Results show that the polarization/depolarization current of natural ester-paper insulation sample is higher than that of mineral oil-paper insulation sample with the same ageing intervals. The depolarization charge quantity of both kinds of oil-paper insulation sample is very sensitive to their ageing conditions. There is an exponential relation between the stable depolarization charge quantity of both kinds of oil-paper insulation sample and the degree of polymerization (DP) of paper. The depolarization charge quantity can be used to predict the ageing condition of oil-paper insulation providing the measurement temperature is kept the same. 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