Showing papers in "IEEE Transactions on Dielectrics and Electrical Insulation in 1999"
TL;DR: In this paper, the authors present a review of the recent performance experience of HV composite polymeric insulators in outdoor service, testing methods, aging, the ranking of the materials, the role of fillers, low molecular weight components present in the insulators, mechanisms responsible for the loss and recovery of hydrophobicity, one of the most important properties of polymers, the mechanisms of failure, detection of faults, type and quantity of natural contaminants, effects of exposure to rain, hydrocarbons, stationary air and wind, various methods to optimize the electrical performance and a
Abstract: HV composite polymeric insulators are being accepted increasingly for use in outdoor installations by the traditionally cautious electric power utilities worldwide. They currently represent -60 to 70% of newly installed HV insulators in Nortb America. The tremendous growth in the applications of non-ceramic composite insulators is due to their advantages over the traditional ceramic and glass insulators. These include light weight, higher mechanical strength to weight ratio, resistance to vandalism, better performance in the presence of heavy pollution in wet conditions, and comparable or better withstand voltage than porcelain or glass insulators. However, because polymeric insulators are relatively new, the expected lifetime and their long-term reliability are not known and therefore are of concern to users. Additionally they might suffer from erosion and tracking in the presence of severe contamination and sustained moisture. This leads to the development of dry band arcing that under certain circumstances could lead to failure of polymer insulators. In this paper a review is presented of the recent performance experience of HV composite polymeric insulators in outdoor service, testing methods, aging, the ranking of the materials, the role of fillers, the role of low molecular weight components present in the insulators, the mechanisms responsible for the loss and recovery of hydrophobicity, one of the most important properties of polymers, the mechanisms of failure, detection of faults, type and quantity of natural contaminants, effects of exposure to rain, hydrocarbons, stationary air and wind, various methods to optimize the electrical performance and a relatively new method for evaluating the performance status of polymeric insulators in the field.
495 citations
TL;DR: In this article, a critical evaluation of the chemical and physical mechanisms responsible for hydrophobicity loss and recovery is presented, where the authors evaluate the properties of silicone rubbers based on polydimethylsiloxane (PDMS).
Abstract: Water repellency, high surface resistivity, vandalism resistance, low density and good processability have made silicone rubbers based on polydimethylsiloxane (PDMS) very attractive materials in housings for outdoor insulation. Their ability to recover hydrophobicity after oxida. tion or contamination is of paramount importance and this is the topic of this review. A critical evaluation of the chemical and physical mechanisms responsible for hydrophobicity loss and recovery is presented.
318 citations
TL;DR: The development of composite insulators in China dates back to the early 1970's and they have become widely used in China in the 1990's and up to 600000 composites are operating on 35 to 500 kV ac overhead transmission lines as discussed by the authors.
Abstract: The development of composite insulators in China dates back to the early 1970's. In the 1990's they have become widely used in China. At present, up to 600000 composite insulators are operating on 35 to 500 kV ac overhead transmission lines. They are to be introduced into the 500 KV HVDC transmission schemes. In China all composite insulators in service are silicone rubber and are operating in various Contamination conditions. They have successfully and efficiently avoided serious pollution flashover, which occurred frequently when conventional ceramic insulators were used, and radically reduced the maintenance cost of transmission lines in pollution areas. Study of composite insulators is very active in China. The main aspects include properties of materials such as silicone rubber and fiberglass reinforced polymer (FRP) rods, electrical and mechanical performance, aging as well as evaluation and inspection of composite insulators. These fruitful works greatly promote the development of composite insulators in China.
219 citations
TL;DR: In this paper, a review of the recent advances in acoustic and optical methods for measuring charge distributions in dielectrics is given, which mainly covers the past research activities associated with that at our laboratory and some of the results that enabled us to gain physical insights into the charge dynamics within solid plate samples and coaxial cables.
Abstract: Much progress had been made during the last two decades in acoustic and optical methods for measuring charge distributions in dielectrics. A review on this topic is given, which mainly covers the past research activities associated with that at our laboratory. For acoustic methods, we will discuss andoompare the pulsed electroacoustic (PEA) and pressure wave propagation (pwP) methods and present some of the results that enabled us to gain physical insights into the charge dynamics within solid plate samples and coaxial cables. For optical methods, we will discuss the Pockels effect technique that is used for the dynamic measurement of surface charge distributions, and the Kerr effect technique that is developed for measuring electric field distributions within liquid dielectrics.
206 citations
TL;DR: In this article, the aging of SIR and hydrophobicity recovery was investigated using both chemical and morphological analysis, and it was shown that oxidation that induces crosslinking, branching, interchanging and a formation of silanol groups are the most dominant chemical reactions during the aging process.
Abstract: This is a laboratory study on the aging of SIR and hydrophobicity recovery. UV radiation, corona discharges, acid rain, dry-band arcing are employed as sources of the aging. Chemical and morphological analysis is used to detect the surface chemical and structural changes derived from these stresses. The nature of highly mobile low molecular weight (LMW) chains achieving a quick recovery of the hydrophobicity is carefully examined. Their generation and extinction caused by these stresses are investigated. From this study, it is shown that oxidation that induces crosslinking, branching, interchanging and a formation of silanol groups are the most dominant chemical reactions during the aging of SIR. Furthermore, silanol groups that are byprodncts of oxidation restrict the diffusion of mobile LMw chains, which decreases the recovery speed of hydrophobicity and accelerates the aging. A typical aging scenario of SIR from the installation to the end of their life is drawn.
175 citations
TL;DR: In this paper, the authors reviewed the unique properties of polydimethylsiloxane (PDMS) elastomers that make it suitable for HV applications and suggested that diffusion of low molecular weight PDMS components is the more important mechanism of hydrophobic recovery.
Abstract: Most of the silicone materials used for Hv outdoor insulation are high-consistency, heat cured polydimethylsiloxane (PDMS) elastomers. The unique properties of PDMS that make it suitable for HV applications are reviewed. The surface of these elastomers can be rendered hydrophilic by exposure to discharges. A time and temperature dependent hydrophobic recovery ensues when exposure ceases. A variety of surface characterization investigations have established that corona exposure forms a brittle, wettable, silica-like layer on the surface of most PDMS elastomers. This is consistent with similar effects from oxygen and inert gas plasma treatment. There is still considerable debate as to the relative importance of the two major mechanisms postulated to account for the hydrophobic recovery after corona discharge. The diffusion mechanism invokes migration of low molecular weight species from the interior to the surface, while the reorientation or overturn mechanism envisages a surface reorganization with polar entities such as silanol groups resulting from surface oxidation rotating away and being replaced by methyl groups in the outermost surface layers. In our view, the highly crosslinked silicalike layer cannot reorient readily between hydrophilic and hydrophobic states at the surface, suggesting that diffusion of low molecular weight PDMS components is the more important mechanism of hydrophobic recovery. Recent data obtained on PDMS samples free from lowmolecular- weight diffusible species show that hydrophobic recovey may be due to in-situ depolymerization.
171 citations
TL;DR: In this article, a survey of the properties of silicone rubber for outdoor insulation is presented and the methods of assessing these properties are discussed and this is followed by a detailed survey of what is known of aging recovery mechanisms.
Abstract: This paper surveys the properties which give silicone rubber its distinctive and highly desirable performance characteristics for use as outdoor insulation. The methods of assessing these properties arediscussed and this is followed byadetailedsurveyof whatis knownof agingaud recovery mechanisms. Corona is identified as the principle electrical aging agent and evidence is presented for irreversible loss of polymer as a result of aging. However, the surface recov. ery mechanisms are robust and, provided there is an adequate resting period, the hydrophobic properties recover, This supports the view, from service experience, that there is no substantial evidence to show that normal aging, unless it results in the exposure of the glass fiber core, detracts from the performance of insulators.
150 citations
TL;DR: In this paper, the authors studied the space-charge behavior in an oxidized crosslinked polyethylene (XLPE) film doped with antioxidant, and proposed a model based on the following assumptions: both electrons and holes are injected from the electrodes and they migrate to the opposite electrodes by hopping transport, holes are also supplied from acceptor sites depending on the field, the holes are excited to the hopping level only via an intermediate level.
Abstract: The packet-like space-charge behaviour in an oxidized crosslinked polyethylene (XLPE) film doped with antioxidant is discussed through computer simulation. The model is based on the following assumptions, (1) both electrons and holes are injected from the electrodes and they migrate to the opposite electrodes by hopping transport, (2) holes are also supplied from acceptor sites depending on the field, (3) the holes are excited to the hopping level only via an intermediate level. In this model, a space-charge packet is not caused by the excess of mobile electrons but by the deficiency in mobile holes. The ionized acceptors left behind by hole migration form an apparent negative space charge packet and it propagates towards the anode as the high field region moves.
113 citations
TL;DR: In this article, the basic properties of streamers, namely the electric field required for a stable propagation and the propagation velocity, have been measured and compared with propagation in air alone as a reference.
Abstract: Results concerning the propagation of streamers along insulating surfaces under uniform electric field are presented. The basic properties of streamers, namely the electric field required for a stable propagation and the propagation velocity, have been measured and compared with propagation in air alone as a reference. The results have shown that in the experimental arrangement used significant space charges due to streamer branching are absent, therefore the properties observed are considered as characteristic of a single streamer. Streamers propagate stably with an intrinsic propagation field and a characteristic velocity that depend on the nature of the insulating material. For electric fields higher than the minimum field required for a stable propagation, a streamer system propagates with a 'surface' and an 'air' component.
109 citations
TL;DR: In-situ conditioning techniques to modify and eliminate the contaminants through multiple HV pulses, low base pressures, RF discharge cleaning, heating, surface coatings and ion-and electron-beam surface treatment allow access to new regimes of performance through control of plasma formation and modification of the plasma properties as discussed by the authors.
Abstract: High-energy pulsed-power devices routinely use field strengths above those at which broad-area, cathode-initiated, HV vacuum-breakdown occur (>10/sup 7/ to 3/spl times/10/sup 7/ V/m). Examples include magnetically-insulated transmission lines and current convolutes, high-current-density electron and ion diodes, high-power microwave devices and cavities and other structures for electrostatic and RF accelerators. Energy deposited in anode surfaces may exceed anode plasma thermal-desorption creation thresholds on the time scale of the pulse. Stimulated desorption by electron or photon bombardment also can lead to plasma formation on electrode or insulator surfaces. Device performance is limited above these thresholds, particularly in pulse length and energy, by the formation and expansion of neutral and plasma layers formed primarily from electrode contaminants. In-situ conditioning techniques to modify and eliminate the contaminants through multiple HV pulses, low base pressures, RF discharge cleaning, heating, surface coatings and ion- and electron-beam surface treatment allow access to new regimes of performance through control of plasma formation and modification of the plasma properties. Experimental and theoretical progress from a variety of devices and small scale experiments with a variety of treatment methods are reviewed and recommendations given for future work.
106 citations
TL;DR: In this article, the authors measured the IR absorption of siloxane migrating to the silicone surface through a thin carbon coating and calculated the time constant for migration, which ranged from 1.6 to 5.3 h depending on alumina trihydrate (ATH) filler concentration.
Abstract: Silicone-based materials for outdoor insulators have the advantage that low molecular weight (LMW) components migrate through the material and coat the surface, thereby restoring hydrophobicity over a period of hours. By measuring the IR absorption of siloxane migrating to the silicone surface through a thin carbon coating, the time constant for migration was calculated. According to the time dependence of IR-absorbance, the time constant for migration ranged from 1.6 to 5.3 h depending on alumina trihydrate (ATH) filler concentration.
TL;DR: In this article, the energy balance in the process of the streamer propagation is calculated for a sub-microsecond discharge in distilled water and it is shown that the energy released in the pre-breakdown process is sufficient to evaporate the liquid in streamer channels.
Abstract: The propagation features of a streamer discharge in water have been investigated. Based on the experimental data obtained in the study of water discharges in a nonuniform electric field, due propagation of streamers is explained as the evaporation of water at the tip of the streamer and around it. The energy balance in the process of the streamer propagation is calculated for a sub-microsecond discharge in distilled water. It is shown that the energy released in the pre-breakdown process is sufficient to evaporate the liquid in the streamer channels. Similar velocity of the streamer propagation in both tap and distilled water substantiates negligible effect of ionic current density onto the streamer propagation process. These estimations, based on experiment, have relevance to the discussion of the nature of the dielectric breakdown of water.
TL;DR: In this article, the authors present measurements of low-level leakage current (LC) patterns on naturally aged insulators and artificially contaminated material samples as well as insulaton, and possible causes for this behavior are discussed and its relations to surface hydrophobicity and electric stress are described.
Abstract: This paper presents measurements of low-level leakage current (LC) patterns on naturally aged insulators and artificially contaminated material samples as well as insulaton. A nonlinear behaviorof the LC has been observed. Possible causes for this behavior are discussed and its relations to surface hydrophobicity and electric stress are described. In addition, neural networks are trained to recognize the LC patterns as well as to estimate their harmonic contents.
TL;DR: In this article, the dc space-charge model was modified to account for the contribution to electrical degradation provided by ac fields, and the results of accelerated life tests performed on various insulating materials, at different values of voltage, temperature and frequency, on the whole finding very good agreement with experimental data.
Abstract: The dc space-charge model, previously developed by the authors, here is modified to account for the contribution to electrical degradation provided by ac fields. First, the dc model is applied to both dc and ac multistress life test results relevant to a given material. The variations of model parameters from dc to ac data fitting provide indications about the modifications in the degradation mechanisms when passing from a dc to ac regime. Then, a description of aging under ac is achieved through proper assumptions about the space-charge buildup, injection mechanism, and dynamic condition of the polymer lattice. This approach enables the effect of frequency to be accounted for, in a framework where ac aging presents significant analogies with mechanical fatigue. The validity of the ac space-charge model is checked by applying it to the results of accelerated life tests performed on various insulating materials, at different values of voltage, temperature and frequency, on the whole finding very good agreement with experimental data.
TL;DR: In this article, a review of room temperature vulcanized (RTV) silicone rubber high voltage insulator coatings (HVIC) is presented, focusing on the important characteristics of these coatings and on the rigorous attention that is required in their application in order to ensure good performance.
Abstract: The paper presents a review of room temperature vulcanized (RTV) silicone rubber high voltage insulator coatings (HVIC). These coatings are designed to replace greasing and waterwashing of insulators. Present day coatings are the result of nearly thirty years of development and use. In all but a very few dirty environments, these coatings have lasted ten or more years without maintenance and where maintenance has been found to be necessary, water washing is done at a significantlyreduced schedule. The paper focuses on the important characteristics of these coatings and on the rigorous attention that is required in their application in order to ensure good performance.
TL;DR: In this paper, the performance of polymers was evaluated in terms of their charge accumulation and decay characteristics as a function of humidity, and their tracking and erosion resistance under AC and DC electrical stresses.
Abstract: An experimental study was conducted to investigate the performance of several polymer outdoor insulator formulations under AC and DC electrical stresses. The performance of the polymers was evaluated in terms of their charge accumulation and decay characteristics as a function of humidity, and their tracking and erosion resistance. The results obtained from this study indicate that significant differences exist in surface charging phenomena between AC and DC. A likely contribution of DC polarization processes leading to hydrophobicity loss is believed to influence additionally the performance of materials subjected to pollution and DC electrical stresses. A substantial reduction in the tracking and erosion resistance of the polymeric materials is observed with DC stresses, in comparison to AC. The poorer electrical performance of the materials stressed with DC voltage was found to be due to higher magnitudes and longer duration times of the discharge current.
TL;DR: In this article, the analysis of spherical conducting particle motion as well as particle initiated breakdown in electric fields between diverging conducting plates with dc voltage in atmospheric air is discussed, where the particle is placed on the horizontal electrode surface where the electric field is nearly equal to the lifting field, the particle progresses towards a higher electric field region by the effect of Coulomb force and electrical gradient force.
Abstract: This paper deals with the analysis of spherical conducting particle motion as well as particle initiated breakdown in electric fields between diverging conducting plates with dc voltage in atmospheric air. Motion of spherical particle was estimated by solving the motion equation numerically, and the results agreed well with the experimental ones. It was found that when the particle is placed on the horizontal electrode surface where the electric field is nearly equal to the lifting field, the particle progresses towards a higher electric field region by the effect of Coulomb force and electrical gradient force. This is true for a nonspherical conducting particle. The obtained results for particle motion suggest that much attention should be paid in the design of GIS particle traps to forces acting on the particle directly towards the higher electric field region. Moreover, the particle-initiated breakdown is discussed on the basis of the experimental and theoretical results. It was found that one of the reasons for reduction of the breakdown voltage is the effect of microdischarge between the particle and an oppositely charged electrode.
TL;DR: A mathematical model of the polarization spectrum is proposed and it is shown that, from the derived model, some of the hidden RVM peaks can be identified.
Abstract: The determination of the polarization spectrum in the low frequency region of the dissipation factor, commonly has been used in practice to diagnose insulation conditions. The recovery voltage method (RVM) is one of the methods used to estimate the polarization spectrum. Nevertheless, current analysis of the RVM tests do not use all the information available from the test. In this paper, a mathematical model of the polarization spectrum is proposed. It is shown that, from the derived model, some of the hidden RVM peaks can be identified. Since the difficulty to derive a model from RVM data increases with the number of the peaks to be identified, a simpler model is always preferable. A scheme for determining the parameters of an equivalent circuit is also given, The composite oil/paper insulation is considered which is extensively used in cables and transformers. Cellulose paper, such as the Manila-Kraft type, which is used as insulation, exerts a major influence on the life of the equipment because of its hygroscopic nature. The importance of detecting and eliminating moisture from paper is crucial in oil-impregnated HV insulation. Analysis of the polarization spectrum has been used by several utilities to determine moisture in the paper. Recently, some test results indicated that the polarization spectrum may not clearly show important peaks corresponding to local moisture ingress and thus can mislead experts in the field, The developed model has been validated using RVM data of real power transformers.
TL;DR: In this article, the authors summarized the results of a questionnaire on current status of non-ceramic (composite) insulators in the world conducted by the NCS Technical Committee, Japan.
Abstract: This paper summarizes the result of the questionnaire on current status of non-ceramic (composite) insulators in the world conducted by the Non-ceramic (composite) Insulators Technical Committee, Japan. Current use status, reasons for use, maintenance, failure occurrence and research activity of 16 responding utilities are described. About 80% of the responding utilities answered that they would actively increase the use of non-ceramic (composite) insulators in the future. It is anticipated that the market for these insulators will keep expanding.
TL;DR: In this paper, the formation and development of dry bands can best be studied by modifying the standard test procedures, which is greatly aided by finite element computation of insulating structures with a conducting surface layer.
Abstract: The formation and development of dry bands can best be studied by modifying the standard test procedures. When such controlled behavior is allied with synchronized optical and electrical recordings, then characterization of the pre-formative leakage current, the transient phenomena associated with partial arcs across dry bands, the location of partial arcs and the voltage drop across dry bands can be determined. Interpretation of test data is greatly aided by finite element computation of insulating structures with a conducting surface layer. When this layer is continuous, this allows straightforward prediction of dry band formation under wetting conditions. Following formation, dry bands can be represented by discontinuities in this layer. Simulation of dry bands with various lengths, when combined with the test data, enables partial arc voltage gradients to be quantified. These results will be discussed in the context of previous work on the pollution flashover mechanism of ceramic insulators.
TL;DR: In this paper, a review of leakage current measurements on nonceramic insulators and material samples is presented, which is divided into two parts: first, the field investigations of LC, include a development of LC measuring systems and how the on-line LC measurements correlate to the insulator performance as well as to the atmospheric and pollution parameters.
Abstract: This paper presents a review of leakage current (Lc) measurements on nonceramic insulators and material samples. It is divided into two parts: First, the field investigations of LC, include a development of LC measuring systems and how the on-line LC measurements correlate to the insulator performance as well as to the atmospheric and pollution parameters. Then, the laho. ratory investigations, describe how the LC are used to evaluate materials, to develop new testingprocedures and to predict insulator performance. An extensive bibliography and additional references is provided.
TL;DR: In this paper, the effect of nonsinusoidal voltage, i.e. voltage affected by the presence of harmonics, on intrinsic aging of cable and capacitor insulating materials, such as cross-linked polyethylene (XLPE) and polypropylene (PP), was investigated.
Abstract: This paper investigates the effect of nonsinusoidal voltage, i.e. voltage affected by the presence of harmonics, on intrinsic aging of cable and capacitor insulating materials, i.e. cross-linked polyethylene (XLPE) and polypropylene (PP). The results of life tests under sinusoidal and distorted voltage, the latter obtained superimposing one or more harmonics on the 50 Hz component, are processed by statistical techniques derived from design-of-experiment procedures. It is shown that the factor predominant on aging acceleration due to the voltage distortion is voltage-peak increase, but also waveform slope and voltage rms value have statistical significance. Life models are obtained for XLPE and PP insulating materials, which show the endurance of the two materials to aging under nonsinusoidal conditions.
TL;DR: In this paper, the authors focus on problems in data analysis and on the interpretation of charge measurements in the bulk and on surfaces, and they focus on the identification of carriers and traps.
Abstract: The electrical currents that flow in and on insulators are small, but they may be important in applications and they may indicate the mechanism of carrier motion. The processes which come into play include mobility and ionization, trapping and detrapping, and injection and blocking. Some of these phenomena are intrinsic to the material, while others depend on the amount and nature of the impurities. This paper concentrates on problems in data analysis and on the interpretation of charge measurements in the bulk and on surfaces. Some materials and some processes are well understood, while others remain obscure, particularly the identities of carriers and traps. A considerable investment of time and money will be required to solve these problems.
TL;DR: In this article, the contamination performance of non-ceramic (NO) and porcelain (Porcelain) insulators is compared with silicone rubher (Rubher) and silicone rubber insulators.
Abstract: The contamination performance of non-ceramic (NO insulators is better than porcelain insulators. The paper describes the pollution collection mechanism and concludes that silicone rubher insulators collect more pollution than porcelain insulators. Long term exposure of silicone rubber insulators produces a thin layer of pollution, which is a mixture of dust, salt and silicone oil. Fog or morning dew produces droplets on the flat surfaces and forms conductive regions. Spot discharge starts between the regions, which reduces hydrophobicity. Simultaneously, dry-band arcing starts on the shank of the insulator. The two arcs join together, which leads to flashover. The flashover voltage of polluted NC insulators is significantly higher than porcelain ones. Insulator performance is measured with laboratory tests. However, salt-fog and clean-fog tests can give different flashover values.
TL;DR: In this paper, the accumulation of space charge in the crosslinked polyethylene (XLPE) insulation of a power cable sample under dc stress was investigated, where the sample was held at 82/spl deg/C and atmospheric pressure, for periods up to several days.
Abstract: The accumulation of space charge in the crosslinked polyethylene (XLPE) insulation of a power cable sample under dc stress was investigated. The sample was held at 82/spl deg/C and atmospheric pressure, and at 82/spl deg/C and 0.1 Pa, for periods up to several days. Such conditioning removed pre-existing space charge, When an external dc field was applied after conditioning at atmospheric pressure and 82/spl deg/C, space charge accumulated at a rate considerably faster than that observed before conditioning. However the rate of accumulation following conditioning at 82/spl deg/C under reduced pressure was much slower than that observed before conditioning. The faster rate could be recovered by reconditioning the sample at atmospheric pressure after conditioning under reduced pressure. Inversion of the equilibrium space charge profile, following reversal of the applied field, was observed. This observation is consistent with a model incorporating a spatially-inhomogeneous polarization in the amorphous volume of the XLPE, and electron injection/extraction at the electrodes. The electron transfer between electrode and XLPE in either direction involves the same narrow window of combined donor and acceptor states in the insulator, centered on the Fermi level. The spatially-inhomogeneous polarization in the XLPE originates in a spatially-inhomogeneous distribution of dipole complexes. It is suggested that the dipoles are formed by a process equivalent to nonpermanent oxidation of the XLPE, requiring water as a catalyst.
TL;DR: In this paper, a data visualization system is presented to display phase-amplitude diagrams for individual partial discharge sources which are identified by the direction of pulse propagation, which can be applied to on-site measurements, type and routine testing of HV cable joints and stress cones.
Abstract: On-site partial discharge (PD) measurement is required to ensure proper installation of extra high voltage (EHV) cable systems accessories. To achieve high sensitivity and good localization, two problems have to be overcome. First, the strong high frequency in long XLPE cables requires that the sensors be located along the cable, preferably directly at the accessories. Secondly, the detection system must be able to distinguish internal PD from other pulses. This paper describes a solution based on directional coupling sensors and a data visualization system, which displays phase-amplitude diagrams for individual PD sources which are identified by the direction of pulse propagation. It has been applied to on-site measurements, type and routine testing of HV cable joints and stress cones. Due to the reliable discrimination between internal PD from the accessory measured and from other pulses, testing can be done in unshielded rooms even using terminations with internal PD and corona. The method works independently well on line voltage, resonance sources, oscillating voltages and 0.1 Hz cosine-square voltage. It has been used to verify the cable accessories installed in the 6.3 km long 380 kV cable system in Berlin, Germany.
TL;DR: In this article, a study of the aging of the materials used as models, and subjected to similar stresses, is undertaken for the voltage, rise time and frequency under study, the intrinsic part of the ageing is studied, according to the nature of the interaction existing between electrical stress and the material properties.
Abstract: The problem of premature failure of rotating machines fed by inverters appears to be of crucial importance. Understanding of the phenomena caused by this new type of supply on the stator insulation of motors provides enhanced reliability of the inverter/motor set. After identifying the stresses created by this type of device, a study of aging of the materials used as models, and subjected to similar stresses, is undertaken. For the voltage, rise time and frequency under study, the intrinsic part of the aging is studied. The results are presented and discussed according to the nature of the interaction existing between the electrical stress and the material properties.
TL;DR: In this article, two different types of composite insulating materials for HV outdoor insulation technology are discussed. And the long-term performance and aging resistance are determined by the interface quality.
Abstract: This paper deals with two different types of composite insulating materials for HV outdoor insulation technology. For outdoor applications fiberglass reinforced polymer (FRP) are used mainly as transmission line insulators (composite long rods),and as power apparatus housings (composite hollow core insulators). During the last decades mineral filled polymer (MFP) are found to be very suitable for outdoor insulation in the medium and HV ranges. To meet the outdoor demands, long-term stability and durability against environmental stresses are necessary, Composite insulation consists of more than one dielectric component, and linking at least two different kinds of materials leads to interface problems. These regions always appear as weak material structures that can be attacked by various aging mechanisms. Especially the long-term performance and aging resistance are determined by the interface quality. One can distinguish four principal kinds of interface: microscopic, e.g. those between fillers and matrix components; macroscopic, e.g. those between glass fiber rod and polymeric shielding material; internal, in the insulation bulk; and external, solid surface against a liquid or gaseous phase. Today the use of composite insulating materials in HV technology is state of the art. They offer a wide range of superior properties for indoor as well as for outdoor applications. Further improvements should focus on the hydrophobicity and on the long term resistance of the external interface and the stability of the internal interface.
TL;DR: In this paper, an artificial single channel was used as model for tree channels to reveal the mechanism of partial discharge (PD) in electrical trees, and a physical model was put forward to describe the PD behaviour.
Abstract: In order to reveal the mechanism of partial discharge (PD) in electrical trees, an artificial single channel is studied as model for tree channels. In a long-narrow channel, the behaviour of PD is similar to that in an actual tree. When the length of the channel is decreased, the /spl phi/-q-n pattern of PD in the channel changes from wing to turtle or rabbit like, and the range of light emission in the channel increases when the applied voltage is increased. Considering the influence of a PD on the total field distribution and thus on a later PD, a physical model is put forward to describe the PD behaviour. It is assumed that PD is induced by the high field at the needle tip, then propagates along the channel, and stops propagating when the field in the channel becomes lower than a critical value due to field divergence. Mathematical analysis on an ideal needle-plane electrode system clearly explains the physical meaning of the model. And the computer simulation by using the superposition method agrees with the experimental results very well. This model is also valid to describe the behaviour of PD in electrical trees.
TL;DR: In this paper, four crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR) insulated cables were subjected to accelerated thermal, radiation, and sequential radiation and thermal exposure to simulate 20, 30, and 40 yr in-service environments in Ontario Hydro Nuclear Plants.
Abstract: Four crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR) insulated cables were subjected to accelerated thermal, radiation, and sequential radiation and thermal exposure to simulate 20, 30, and 40 yr in-service environments in Ontario Hydro Nuclear Plants. Two sets of samples were evaluated. The first set contained 15 cm cable specimens in tubular form with the conductors removed, while the second set was made up of 4.3 m cable samples wound on mandrels. The cable samples were sequentially irradiated and thermally aged and subjected to an additional accident radiation exposure followed by a simulated loss of coolant accident (LOCA)/main steam line break (MSLB) steam test. During the steam test, samples were energized and their electrical characteristics continuously monitored. The material performance of the insulation was assessed using the 15 cm specimens during the various stages of aging exposure by conventional elongation measurement and by the use of micro-specimens with differential scanning calorimeter (DSC), oxidation induction time (OIT) and infrared carbonyl absorption techniques. The results from these samples were compared with the electrical performance of the cable samples wound on mandrels that had been subjected to the LOCA/MSLB steam test. The test results indicate that with the use of micro-specimens meaningful changes were obtained until the elongation values of the samples were reduced to 50% absolute. Electrical test data obtained for XLPE and EPR during the steam tests indicate that 50% absolute elongation values provide sufficient margin to withstand additional accident radiation, and to function electrically during design basis events.