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For more reliable HVDC power transmission systems, it is necessary to enhance HVDC electrical insulation performance in power equipment such as an oil-immersed AC/DC converter transformer. In this paper, the electric field distributions under AC, DC steady-state (DC-SS) and DC polarity reversal (DC-PR) conditions are discussed in oil-pressboard (PB) composite insulation structures. Firstly, based on discussion about the charge accumulation and charge dynamics at oil/PB interfaces, the contribution ratio of deposited charges under DC-SS to the following emerging electric stresses at DC-PR conditions are quantitatively clarified. Secondly, we found that the DC electric field distributions could significantly be controlled by PB arrangement in oil. In particular, both PB configurations and the conductivity ratios of oil and PB would play critical roles to determine electric field distribution, under DC-SS conditions. Furthermore, using an actual AC/DC converter transformer structure, electrical insulation performances under various testing conditions such as AC, DC-SS and DC-PR conditions were comparatively investigated. It was concluded that the most critical testing condition against breakdown strength could be the DC-PR conditions under the higher conductivity ratio of oil and PB. [ABSTRACT FROM AUTHOR]

For the development of HVDC electrical insulation performance in liquid dielectric systems such as oil-pressboard (PB) composite systems in DC converter transformers, a Kerr electro-optic electric field measurement (Kerr-EOM) technique has been well established and will be considered as the key technique to be introduced. In this paper, the Kerr-EOM was experimentally applied to identify the electric field stress distribution and clarify charging activities in oil/PB composite insulation systems, under HVDC and DC polarity reversal (DC-PR) conditions. The physical mechanisms of charge movement and the amount of charge accumulation in liquid/solid insulation systems are also thoroughly investigated and discussed. Moreover, the breakdown discharge initiation by accumulated charges on the PB was observed and discussed together with the field measurement results. Secondly, by combining the Kerr-EOM with the electric field analysis using the Finite Element Method (FEM), the enhancement of the electrical insulation performance for HVDC applications was discussed and the critical testing voltage conditions in DC converter transformers were addressed. This paper is based on the Hans Tropper Memorial Lecture given at the IEEE DEIS, International Conference on Dielectric Liquids (ICDL) in 2017 in Manchester, UK. [ABSTRACT FROM AUTHOR]

Introduction of metal oxide nanoparticles to polymer material is known to have unique dielectric behavior and significant advantages in electrical insulation performance in power apparatus. This paper presents an attempt to clarify the influence of dispersibility of nanoparticles, especially focusing on agglomerates, on dielectric properties of a nanocomposite system by changing particle dispersion processes. Experiments were carried out in epoxy/alumina nanocomposites with the particle dispersion techniques by applying ultrasonic wave and centrifugal force. For the dispersibility control of nanoparticles, we changed the duration of ultrasonic wave and centrifugal force. The experimental results clarified the effect of centrifugal force on the separation of agglomerates and the effect of ultrasonic wave on the disruption of agglomerates. Next, we examined the dielectric properties such as relative permittivity and tan δ of the nanocomposites. As the result, we verified that the permittivity of epoxy/alumina nanocomposites became low due to separation and disruption effects of the agglomerates. [ABSTRACT FROM AUTHOR]

This paper reviews the up-to-date research activities on electrical insulation techniques under repetitive surge voltages with steep wavefront for low voltage inverter-fed motors. Partial discharge (PD) inception, propagation, ageing and breakdown characteristics of magnet wires, including recently developed PD-resistant wires such as nanocomposite enameled wires, are described. PD measurement techniques under the steep-front voltages and IEC activity toward their standardization are also introduced. [ABSTRACT FROM AUTHOR]

A novel technique for partial discharge (PD) measurement and analysis (PD-CPWA PD Current Pulse Waveform Analysis) is developed and introduced in this paper. PD-CPWA is expected to be utilized to discuss PD mechanisms and physics in electrical insulating materials, focusing on the PD current pulse waveform and its time transition from PD inception to breakdown (BD). In this paper, the concept and principle of PD-CPWA are described, and the applications of PD-CPWA to (1) epoxy spacer samples under thermal and electric combined stresses in GIS, (2) creepage PD on epoxy spacers in SF6 gas and (3) liquid nitrogen / polypropylene laminated paper composite insulation system for high temperature superconducting cables are introduced and discussed. [ABSTRACT FROM AUTHOR]

We studied changes in serum levels of hepatocytes growth factor (HGF), as well as the levels of HGF expression in the livers, of rats with chemically-induced cancer. Rats were given diethylnitrosamine (DEN) orally in their drinking water. The serum HGF level was measured by enzyme-linked immunosorbent assay. The degree of HGF expression in liver, detected by immunoperoxidase staining, was classified from negative to high. For two DEN-treated rats, the nucleotide sequence of HGF DNA was determined from the livers containing cancerous foci (CA). The serum HGF levels tended to be higher in the DEN-treated rats than in the control rats. In the DEN-treated rats, low to moderate levels of expression of HGF were found in hepatocytes with strong atypia at 8, 12, and 14 weeks. Low levels of HGF expression were found in moderately differentiated cancer cells. The sequence of HGF showed the loss of three nucleotides, in comparison with a sequence reported previously. In conclusion, the results of this study suggest that HGF may contribute to hepatocarcinogenesis in chemically induced cancer in rats. [Copyright &y& Elsevier]

Binding of a helicene, 5,8-bis(aminomethyl)-1,12-dimethylbenzo[c]phenanthrene, to calf thymus DNA was studied using UV, CD, and fluorescence spectroscopy as well as calorimetry. The enantiomeric helicenes strongly bound to the double strand DNA possessing the right-handed helical structure. In addition, chiral recognition was observed in the binding, where the (P)-helicene with the right-handed helicity formed more stable complex than the (M)-helicene with the left-handed helicity. The binding studies of the helicenes and natural nucleosides by 1H NMR spectroscopy also revealed the higher affinity to the (P)-helicene. Both monomeric and polymeric nucleic acids thus turned out to favor the (P)-helicity. [Copyright &y& Elsevier]

Diastereomeric triamines containing two helicene moieties, 1,12-dimethylbenzo[c]phenanthrene, were synthesized and found to form folded structures in the water. Such folding was not observed for an achiral compound possessing a naphthalene moiety. The (M,M)-dihelicenetriamine with matching configuration at the helicene moieties formed a more stable folded structure than the (P,M)-isomer containing two enantiomeric helicene groups. The most stable folded conformation was predicted by the Monte Carlo method with Amber force field of the dihelicenetriamine. [Copyright &y& Elsevier]

Investigates the synthesis of cycloamides using a building block method. Components of the building block method; Activation of acid terminal as acid chloride; Structural properties of cycloamides.

Examines the synthesis of symmetrical polynitrohelicenes. Chiral recognition in the charge transfer complexation of electron-deficient helicenes; Example of the selective aromatic polyfunctionalization; Functionalization of polycyclic aromatic compounds.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a member of the coronavirus family that also includes endemic human coronaviruses (HCoVs) types OC43, HKU1, 229E, and NL63. HCoVs share extensive sequence homology with SARS-CoV-2. It has been assumed that HCoV infection occur primarily in winter and spring in Japan before the coronavirus disease 2019 (COVID-19) pandemic and that its frequency is the same for all age groups. Nasopharyngeal swab samples were collected for HCoVs and SARS-CoV-2. All medical data were retrospectively analyzed. Our primary objective was to describe the epidemiology of HCoV in the Furano, Japan during the COVID-19 pandemic. Our secondary objective was to compare the prevalence of HCoV with that of SARS-CoV-2. From September 2020 to August 2022, 113 (6.2 %) of 1823 cases were positive for any HCoV. The HCoV-NL63 activity peaked in January–March 2021. The HCoV-OC43 activity peaked in June–August 2021. HCoVs were mostly detected at age ≤11 years and most frequently at age ≤2 years. HCoVs showed high detection in 2021, while SARS-CoV-2 showed moderate detection in 2020–2021, but significantly increased in 2022. During the COVID-19 pandemic, HCoV-OC43 activity peaked in the summer. The frequency of HCoV infection varied widely by age group and was higher among those aged ≤11 years. These were different from those reported before the COVID-19 pandemic. These findings suggest that the disease dynamics of HCoVs remain unclear and that continued surveillance is essential in the post-COVID-19 pandemic. [ABSTRACT FROM AUTHOR]

Provides information on a study which examined the configuration of macrocyclic amides consisting of helical chiral 1,12-dimethylbenzo[c]phenanthrene-5,8-dicarboxylate. Results and discussion; Experimental methods.

This paper describes the development of three-dimensional electric field analysis by using the so-called segment method which enables the electric field to be calculated with high accuracy and with enhanced efficiency, for high-voltage apparatus. In the segment method, electrode configuration of high-voltage apparatus is simulated by small components which are called segments and by the arrangement of several kinds of such segments. In this calculation, the charge simulation method is used which is suitable for segment application. As basic segments, spherical, cylindrical and ring segments are used and in addition to these, as subsegments, discs and elbow segments are adopted for good simulation of the total electrode configuration. In this paper, the fundamental construction and arrangement parameter of segments were discussed. Moreover, the segment method was applied to an actual high-voltage apparatus and the calculation accuracy was discussed. It was clarified that the segment method has sufficient calculation accuracy and is a very efficient means for three-dimensional electric field analysis. [ABSTRACT FROM AUTHOR]

The article discusses the development of 1 gigahertz (GHz) gas-insulated switchgear surge sensor. One of the structural features of surge sensor is the connection method of a floating electrode and coaxial cable that utilizes a cone-shaped coaxial structure. 350 picosecond was obtained as the step response time, confirming that the sensor possesses the frequency band of 1 GHz. The appropriate matching of the coaxial cable is important when connecting surge sensor with oscilloscope.

In this study we investigate the time and space transition characteristics of DC electric field in SF 6 gas from the initial state DC-on to final DC steady-state in gas-solid composite insulation systems. Using a simple rod-electrode configuration and actual insulating epoxy-spacer model, the electric field distributions of the epoxy-spacer in SF 6 gas and time constant T of electric field formation from DC-on to DC steady-state are calculated based on the electric conduction characteristics. In addition, the emerging electric field distributions due to accumulated charge on solid insulator surface are introduced to elucidate the time transition process of electric field stress in the gap between HV conductor and GND. As a result, we quantitatively clarify that the time constant T of electric field formation are highly dependent on the non-uniform factor η and location of the gap space in the electrode configuration under non-uniform DC electric field. The locations with higher electric field stress in the gap space have the shorter time constant T. In addition, the time transition process of electric field stress in SF 6 gas depends on the gap space and the location of maximum electric field change during time transition. Especially, we clarify that the highest electric field stress in SF 6 gas may emerge in actual GIS structure based on the time transition process of emerging electric field due to accumulated charge. [ABSTRACT FROM AUTHOR]

The article presents a case study of 20 of 23 patients who were treated with baloxavir marboxil (BM) and an examination of 65 patients who received BM in their fight against influenza. Topics include how Delayed BM therapy (≥48 h after onset) was associated with prolonged fever duration and how BM had more effect on influenza B than neuraminidase inhibitors (NAI).

Research and development results of enhancement techniques of electrical insulation performance for higher electric field application in power transmission/substation equipment, such as transformers, switchgears and cables, are described, especially based on the view point of dielectric materials. Firstly, the electric field analysis, field optimization and field measurement techniques are introduced to discuss higher electric field stress applications in power equipment. Secondly, material types, including gases, liquids, solids, vacuum and their composite systems are discussed to make power equipment with higher insulation performance, lower losses, lower environmental impact and higher reliability. In the process of development, a highly sophisticated new approach to clarify the physical mechanisms of partial discharges was developed and applied. By the introduction and applications of the above mentioned new electrical insulation techniques based on dielectric materials, concepts of future power equipment with higher electric field stress are proposed. This paper is based on the Whitehead Memorial Lecture given at the IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP) 2011 in Cancun, Mexico. [ABSTRACT FROM PUBLISHER]

The article introduces the special issue of "IEEE Transactions on Dielectrics and Electrical Insulation." The special issue is devoted to various aspects of electrical discharges and electrical insulation in vacuum. The papers are mostly based on expanded presentations that were given at the XXII IEEE International Symposium on Discharges and Electrical Insulation in Vacuum which was held in Matsue, Japan in September 2006.

For power transformer insulating oil, we focused on palm oil fatty acid ester (PFAE). It has satisfactory insulating performance, excellent cooling ability and superior biodegradability. Recently, investigations for application of PFAE to environment- friendly power transformers installations have been started. In this paper, the space charge behavior in PFAE was investigated from the measurement results of the electric field by using Kerr electro-optic method under dc voltages applications. For the field measurement, the Kerr constant of PFAE was identified first. Then, the electric field strength and its temporal change were measured in several PFAE I pressboard (PB) insulation systems. The electric field in PFAE was determined by the capacitive distribution at the moment of the voltage application, and decreased rapidly with time and reached the steady state determined by the resistive distribution. The transition time of the capacitive distribution to the resistive one and the strength of electric field in PFAE were much different from those in mineral oil. The influence of oil flow on the time transition of the electric field was also measured. Their differences were discussed with the charge behavior in liquids, based on electro-chemical properties of the oil. We discussed the difference of the flow electrification characteristics between PFAE and mineral oil, and its mechanism was discussed based on the charge behavior in oils. [ABSTRACT FROM AUTHOR]

Gas insulated Switchgears (GIS) are widely used as major substation equipment because of their excellent insulation and interruption performance. However, while a GIS is highly reliable, it is a concealed device, meaning diagnostic technology using various sensors is required to detect any insulation abnormality. Among various potential defects inside a GIS, the most problematic is caused by the existence of fine metallic particles, and thus the ability to detect harmful particles in tests at a factory and on site as well as in operation is becoming an important subject. This paper examines, on an experimental basis, the UHF sensor's characteristics of detecting partial discharge (PD) signals generated from particles inside the GIS with those placed freely on the bottom surface of the tank, having adhered to the insulating spacer's surface, and fixed on the center conductor, respectively. Based on previous reports, breakdown characteristics with the existence of particles were arranged in terms of the particle length, and the harmful particle length was estimated. Both results were compared with each other to evaluate the possibility of detecting harmful particles in each location with the UHF sensor. Consequently, it emerged that free particles were detected comparatively easily. However, while those having adhered to the spacer's surface and fixed on the center conductor could be detected in insulation tests at 2 Pu at a factory, detection was difficult in many cases in the field. [ABSTRACT FROM AUTHOR]

For the size reduction of electric power equipment, the electric field stress around solid insulators is to be carefully designed. This concern will be solved by the application of FGM (Functionally Graded Materials). In this paper, we investigated an application feasibility of FGM from numerical simulation, and the fabrication technique for gas insulated equipment. Finally, we could confirm the significant effect of FGM application for gas insulated equipment. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(2): 39–45, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20363 [ABSTRACT FROM AUTHOR]

In inverter-fed motor coils, surge voltages with the rise time of several tens or hundreds of nano-second may cause partial discharge (PD) and degradation of electrical insulation performance of the inverter-fed motor coils. This paper discusses PD inception characteristics as well as PD propagation characteristics after PD inception for magnet wire of inverter-fed motor under surge voltage application. Experimental results firstly revealed that PD inception voltage (PDIV) decreased with the increase in the length of enamel-coated wire, which was evaluated in terms of the stressed wire contact length under surge voltage application, i.e. size effect. We proposed a regression line for the size effect on PDIV for the electrical insulation design of inverter-fed motor coils. Secondly, PD propagation characteristics were also investigated under the higher voltage application, and their mechanisms were discussed in terms of generation probability of initial electrons, space charge behavior in the wedge-shaped air gap, charging on the enamel surface and so on. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) may take place due to residual defects like metallic particles in SF6 gas-insulated power apparatus such as GIS. However, the signal of PD occurring in SF6 gas is very weak and susceptible to external noise in air. Moreover, because of the complicated mechanism of PD, the radiation property of electromagnetic waves from PD has not as yet been clarified. Therefore, it is hard to distinguish the PD signal in SF6 gas from external noise. From the above points of view, we have been investigating the radiation mechanism of electromagnetic waves from PD. We measured the polarization characteristics of electromagnetic waves radiated from PD in comparison with those of half-wave dipole antennas. The polarization characteristics of PD were explained by the theory of half-wave dipole antenna, rather than that of an infinitesimal dipole antenna. Moreover, we compared the power spectrum for PD measured using a biconical antenna with that received from the half-wave dipole antenna or infinitesimal dipole. It was found that the power spectrum for PD also corresponded to that for the half-wave dipole antenna with a length of 50 cm. © 1999 Scripta Technica, Electr Eng Jpn, 126(4): 40–47, 1999 [ABSTRACT FROM AUTHOR]

Focuses on insulating characteristics of SF6 small gas against lightning impulse voltages. Ion density in gas gaps; Generation of initial electrons; Influence of surface roughness of electrodes.

Presents a theoretical study of metallic particle motion and particle initiated breakdown in gas-insulated switchgear. Motion equation; Calculation results; Crossing electric fields; Electric charges.

In AC/DC converter transformers under DC application, the electric field distributions are distorted due to the accumulated charge on pressboard. However, the time‐dependent characteristics of DC electric field stress in oil has not yet been clarified in detail. In this paper, we investigated the time and electric field space transition characteristics of DC electric field distributions in oil‐pressboard composite insulation systems. As a result, we quantitatively clarified that DC electric field stress strongly depends on the elapsed time and the location in the electric field space in oil. In particular, it was found that the most severe electric field stress in oil may emerge during the time transition process. [ABSTRACT FROM AUTHOR]

A calculation model for predicting the inception of partial discharge (PD) in a non-uniform air gap on the basis of theories of electron avalanche and streamer phenomena is proposed. ?Partial discharge inception voltages? (PDIVs), under an assumed absolute humidity of less than 20g/cm3, calculated using the proposed model were compared with experimentally measured ones and found to be almost equivalent. Furthermore, the relationship between negative ions and humidity was incorporated into the calculation model, and it was confirmed that the calculated and measured PDIVs tend to be the roughly the same under a wide humidity range under various gap length between electrodes. The proposed partial-discharge inception model based on theories mentioned above was therefore judged to be effective for predicting changes in PDIV when humidity changes. [ABSTRACT FROM PUBLISHER]

An innovation for the higher performance and reliability of electric power apparatus can be brought about by a novel technique on electrical insulating materials. The application of functionally graded materials (FGM) with spatial distribution of dielectric permittivity in solid insulator is an effective technique to contribute to the above innovation, because FGM can control the electric field distribution with a simple shape. In this paper, we investigated the fabrication and simulation techniques of FGM with various spatial distributions of dielectric permittivity using centrifugal force. Firstly, we developed a simulation technique to estimate the dielectric permittivity distribution of FGM by considering the particle movement in a viscous fluid under centrifugal force. Secondly, based on the simulation technique, we fabricated FGM samples with various relative permittivity distribution and confirmed the validity of the simulation technique. Consequently, the fabrication results provided a good agreement with the simulation results. [ABSTRACT FROM PUBLISHER]

To clarify the breakdown mechanism and the conditions leading to the breakdown under non-uniform electric field in air, we studied the details of breakdown characteristics and mechanism in air by using an ultra-high speed measurement system. We clarified that there were two types of breakdown mechanism in air. The one is the channel heating breakdown, and the other is the leader-type channel development breakdown. These breakdown mechanisms are dominated by three conditions: arrival of secondary streamer from high-voltage anode to opposite grounded cathode, channel heating, and leader-type channel initiation. We studied these conditions quantitatively, and revealed the conditions leading to the breakdown, and the breakdown mechanisms in air were classified. Finally, we clarified the factors, e.g. critical instantaneous power for the secondary streamer arrival, dominating these conditions based on the breakdown mechanism under non-uniform electric field in air. [ABSTRACT FROM PUBLISHER]

Background Little is known about the clinical effectiveness of neuraminidase inhibitors against H275Y influenza A(H1N1)pdm09 virus. A cluster of H275Y influenza A(H1N1)pdm09 virus with cross-resistance to oseltamivir and peramivir was detected among untreated community patients in Hokkaido, Japan, during the 2013-2014 influenza season. Methods This was a retrospective observational study. Specimens from nasopharyngeal swabs underwent rapid testing and single-nucleotide polymorphism identification on real-time polymerase chain reaction. We collected clinical data from the H275Y group and a 275H wild-type comparison group. All children were given one of four neuraminidase inhibitors. Results Twenty-eight children infected with influenza A(H1N1)pdm09 virus were analyzed. Ten viruses had the H275Y substitution, while the other 18 had wild-type 275H. Mean fever duration after treatment and after onset was 25.3 h (95%CI: 14.1-36.5) and 48.9 h (95%CI: 34.4-63.3) in the H275Y group, respectively, and 26.1 h (95%CI: 18.7-33.6) and 46.3 h (95%CI: 35.7-56.8) in the 275H group, respectively. In the H275Y group, three patients were treated with oseltamivir, one with peramivir, five with zanamivir, and one with laninamivir. All of them had mild symptoms and received only outpatient care. Fever duration was 7.5-21.0 h and 18.0-66.0 h after treatment and after onset, respectively, in the patients treated with oseltamivir and peramivir, and 20.5-42.0 h and 42.0-88.0 h, respectively, in those treated with zanamivir and laninamivir. Conclusion Fever in the H275Y children treated with oseltamivir and peramivir resolved rapidly during the 2013-2014 influenza season. [ABSTRACT FROM AUTHOR]

Toward the practical and rational insulation design of high temperature superconducting power apparatus, the ac breakdown (BD) characteristics and mechanisms of liquid nitrogen (LN2) were systematically investigated and discussed for different pressures at P = 0.1-0.3 MPa and temperatures at T = 65-77 K under quasiuniform electric field with the field utilization factor ζ= 0.986-0.674. We obtained the BD strength (EB) in sub-cooled LN2 (SLN2) and analyzed them in terms of size effect, taking account of the stressed liquid volume (SLV) with the electric field distribution in SLN2. Together with the other researchers? data on BD characteristics of LN2, we extended the evaluation by applying the concept of α% SLV (SLV with the electric field strength higher than the decisive electric field factor, α of the maximum electric field strength). As the result, we derived that EB with the 50 % probability decreased linearly with the increase in α% SLV on a universal line, EB = 78.4 x (α% SLV)-1/8.15, which was irrespective of the pressure and temperature of LN2. [ABSTRACT FROM AUTHOR]

Gas insulated switchgears (GIS) have been increasingly introduced as main substation equipment since the late 1960s thanks to their high reliability, safety, and compactness. The UHF method to diagnose partial discharge (PD) is broadly employed in the field as an advanced insulation diagnostic technology. There are three primary factors related to the PD signal detection characteristics using this UHF method; namely the frequency spectrum of the PD signal itself inside GIS, the propagation characteristics of the PD signal inside the GIS tank, and the detection characteristics of the sensor measuring the PD signal. Accordingly, to further improvement of the diagnostic technique based on the UHF method, the PD phenomenon itself and its propagation characteristics should be clarified and the measurement system refined. From these perspectives, the present study reviewed the recent and latest findings concerning the PD phenomenon and its propagation characteristics inside GIS as well as the PD measurement system verification methods and diagnostic technologies, and summarized typical examples. Firstly, with regard to the PD phenomenon, measurement up to the high frequency band exceeding 10 GHz (even 30 GHz) clarified that the rise time of the PD current waveform is several tens of picoseconds, shorter than previously known. In the case of PD in micro-defects inside the epoxy insulator, however, the rise time is relatively long, in the order of nanoseconds, and a crack is the most critical defect. Subsequently, with regard to UHF PD diagnostics/monitoring technology, a novel technique using PD current waveform characteristics has been developed, and a more advanced PD diagnostic algorithm has been established by clarifying the influence of the shape and GIS internal structures on the electromagnetic wave propagation characteristics. Less uncertain and simplified calibration and verification technologies are also proposed both for a single UHF sensor and the entire UHF measurement system. These new technologies and further advanced studies in future are expected to make the UHF method more convenient and sophisticated. [ABSTRACT FROM AUTHOR]

Surface discharge on solid insulators is one of the significant issues in the development of vacuum circuit breakers (VCB) and vacuum interrupters (VI). We measured the charge activity on alumina dielectrics in vacuum through ultra-high speed and high sensitivity optical measurements. We identified the existence of charge activity with a small light emission on alumina dielectrics before the surface flashover development process, and defined this as a "pre-discharge" and measured its characteristics. We classified the charge activities into three processes: (1) pre-discharge, (2) surface flashover initiation, and (3) surface flashover expansion, in the development of surface discharge in vacuum. Utilizing this classification, we found that the surface predischarge in vacuum is generated by the electron emission from the cathode, and the subsequent flashover initiates with a steep increase in current and develops with the distortion of the electric field due to transiently-formed charging on the alumina dielectrics in vacuum. [ABSTRACT FROM AUTHOR]

The relationship between the PD current pulse waveform at the PD source and the radiated electromagnetic (EM) waveform is investigated using a needle electrode for a metallic particle in SF6 gas at 0.2MPa. A leader discharge with a larger PD charge magnitude and a longer propagation length than for a streamer discharge can be an indicator of breakdown in the SF6 gas. Simultaneous and synchronous measurement of the PD current, EM signals and light emission in the SF6 gas revealed that it is possible to discriminate between a streamer discharge and a leader discharge in both time and frequency components. Compared with a streamer discharge, a leader discharge is characterized by a longer rise/fall time of around 0.9 ns in the PD current pulse waveform, and by a lower frequency component of around 250 MHz in the EM frequency spectrum. A satisfactory correlation was obtained between the actual measured EM wave spectrum and the spectrum derived using a spectrum analyzer from the product of the actual PD current and the transfer function from the needle electrode to the UHF sensor that receives the EM wave. This new technique enables streamer and leader types of PD in SF6 gas to be discriminated between by measuring the EM wave with a UHF detection system. [ABSTRACT FROM AUTHOR]

For proper insulation design of epoxy cast resin power apparatus such as molded transformers, it is important to consider the criticality of defects that might exist into the dielectric material. One of the most important defects is the delamination defect at the interface between resin and conductor. Accordingly, this paper aims to investigate partial discharge (PD) characteristics and to clarify their mechanisms for micro gap delamination defect of epoxy cast resin power apparatus. An experimental model simulating delamination defect was built. Nitrogen gas at atmospheric pressure was used as a typical filled gas inside the delamination of epoxy cast resin power apparatus. Simultaneous measurements of PD light emission intensity, PD light emission image and PD current pulse were carried out. PD inception voltage was measured for different delamination depths. PD generation characteristics were recorded. It was found that multiple PD events were detected only by PD light emission images and could not be detected by their current pulses as a result of very small magnitudes of PD current pulses. Time transition of PD activity for 10 minutes were obtained and analyzed using the captured light emission images. Based on the obtained results and comparing with SF6 gas filled delamination, physical mechanisms behind PD activity could be discussed. [ABSTRACT FROM PUBLISHER]

This paper discusses a novel estimation method for partial discharge inception voltage (PDIV) of magnet wire under inverter surge voltage application. We focused on the generation probability of initial electrons, which induce PD under high electric field and short rise time of surge voltage, by means of Volume-Time theory. We applied the Volume-Time theory to PD inception phenomena in a wedge-shaped air gap of twisted pair samples composed of enameled wires, and estimated PDIV in consideration of initial electron generation probability with temporal and spatial change in electric field distribution. We could estimate PDIV under different waveforms of applied surge voltage for different specifications of enameled wires. PDIV estimated by the extended Volume-Time theory agreed well with the measured PDIV. The estimated PDIV decreased with the increase in the rise time of applied voltage waveform, which corresponded to the V-t characteristics in the time range of inverter surge voltage. [ABSTRACT FROM AUTHOR]

We propose a high-temperature superconducting fault-current-limiting cable (SFCLC), which is a hightemperature superconducting cable with a fault-current-limiting function. The SFCLC is expected to achieve fault-current limitation by flux-flow resistance of a long cable length. Particularly, in this paper, we focus on E–I –T characteristics of a YBCO-coated conductor at the flux-flow region. Based on the obtained E– I–T characteristics, we develop a numerical model and investigate current-limiting characteristics of the SFCLC for different cable lengths and fault conditions into a model power system. [ABSTRACT FROM AUTHOR]

We have been developing Superconducting Fault Current Limiting Transformer (SFCLT) with the function of both superconducting transformer in steady state and superconducting fault current limiter in fault condition. As the Step-5 of SFCLT project, 2 MVA class HTS-SFCLT using YBCO coated conductors with the ratings of 22 kV/6.6 kV has been developed. One of the important concerns for the development of HTS-SFCLT is the current limiting and recovery characteristics as well as the transformer function. Thus, in this paper, current limitation and recovery tests of the HTS-SFCLT are carried out. The current limiting test have revealed that the HTS-SFCLT exhibits the excellent current limiting function as a superconducting fault current limiter, where the prospective short-circuit current IPRO=784\ \rm Apeak is reduced to 34% at the first peak and 18% at the 5th cycles. The HTS-SFCLT has been able to recover into superconducting state immediately after the fault clearance. According to the transition of generated resistance of the HTS-SFCLT, the criteria of recovery into superconducting state are quantified for different combinations of load current before the fault and prospective short-circuit current during the fault. [ABSTRACT FROM AUTHOR]

We have been developing Superconducting Fault Current Limiting Transformer (SFCLT), which has multifunction of both a superconducting transformer in a steady state as well as a superconducting fault current limiter in a fault condition. This paper introduces the progress in our SFCLT project since 1998, from Step-1 to the latest Step-5, with the concept, design, fabrication and test results of SFCLT. In the latest Step-5, we developed a 2 MVA, 22/6.6 kV class SFCLT with YBCO coated conductors and verified the fundamental function as a transformer, effective current limiting function as a fault current limiter, and recovery characteristics after the fault clearance with its operational criterion. [ABSTRACT FROM AUTHOR]

Electrode conditioning is a very important technique for improvement of the insulation performance of vacuum circuit breakers (VCBs). This paper discusses the spark conditioning mechanism under a nonuniform electric field, focusing on the pre-breakdown current. We quantitatively evaluated the spark conditioning effect by analyzing the pre-breakdown current based on the Fowler-Nordheim equation. The field enhancement factor β was found to decrease with increasing breakdown voltage at the beginning of the conditioning process, and finally became saturated with the saturation of the breakdown voltage. In addition, in the case of a nonuniform field, we found that β on a high-voltage rod electrode after conditioning varied according to the electric field strength on the rod electrode. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(2): 21-28, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21059 [ABSTRACT FROM AUTHOR]

For accurate detection and diagnosis of Partial Discharges (PDs) in Gas Insulated Switchgears (GISs), there is a need for better understanding of the physical mechanisms for the PD activity. Accordingly, we have been investigating the PD characteristics and associated mechanisms for electrode/epoxy delamination of GIS spacers as one of the severest defects in GIS. The gas pressure inside delamination usually changes from sub-atmospheric pressure, just after delamination initiates, to filled SF6 gas pressure in the GIS tank, after SF6 gas infiltrates into the delamination area. Therefore, in this paper, the PD activity at different gas pressures, from 0.02 to 0.4 MPa, is acquired. Delamination gap length at the level of 50 µm is considered, simulating possible size of actual delamination in a GIS spacer. The relative PD generation rate is analyzed regarding the phase characteristics at different pressures and then discussed from the viewpoint of PD mechanism in order to assess the possibility of delamination diagnosis in GIS spacers. Experimental results show that, PD parameters and phase characteristics change significantly with infiltrating SF6 gas from the GIS tank into the delamination. The obtained results give a characterized feature for the delamination defect and can be useful for delamination diagnosis. [ABSTRACT FROM AUTHOR]

For the size reduction and the enhancing reliability of electric power equipment, the electric field stress around solid insulators should be considered enough. For the relaxation of the field stress, the application of FGM (Functionally Graded Materials) with spatial distribution of dielectric permittivity (ϵ-FGM) can be an effective solution. In this paper, we investigated the applicability of ϵ-FGM for reducing the electric field stress on the electrode surface with contact to the solid dielectrics, which was one of the important factors dominating a long-term reliability of the insulating spacer. Firstly, we carried out numerical simulation of electric field to confirm the reduction of the electric stress by U-shape permittivity distribution. Secondly, we investigated the fabrication feasibility of ϵ-FGM with the U-shape distribution. Thirdly, we estimated the longterm electrical insulation performance of the ϵ-FGM. Finally, we verified the applicability and the fabrication technique of the ϵ-FGM to solid dielectrics for improvement of the electric stress and the long-term insulation performance in electric power equipment. [ABSTRACT FROM AUTHOR]

The partial discharge (PD) measurements are considered as the most important tool for condition monitoring of Gas Insulated Switchgears (GISs). However, if spacer surface is involved in PD activity, charge accumulation process greatly affects the time transition of PD characteristics. This paper investigates this effect considering the defect types of delamination at the electrode/spacer interface and metallic particles adhered to the spacer surface as the most serious defects that can lead to major failure. Two different electrode configurations were built to simulate the two defect types. The PD characteristics were measured and analyzed from immediately after voltage application up to several minutes where steady state characteristics have been obtained. As a result, it was found that the generation rate of PD pulses changed considerably with time for both defect types. This tendency of PD characteristics has been discussed considering the effect of charge accumulation. Comparing these effects for negative and positive PD enabled to clarify the similarities and differences in the charge accumulation effect for both defect types which can contribute to the defect type identification in GIS. It was found that the effects of charge accumulation on the electric field strength for the delamination defect case as well as on the ionization volume for the metallic particle case were the responsible parameters for the different PD tendencies. [ABSTRACT FROM AUTHOR]

For higher electrical insulator performance of vacuum circuit breakers (VCB), the surface flashover in vacuum should be improved. In particular, it is important to clarify how strongly surface charges influence the surface flashover mechanism. In this paper, we investigated the surface flashover characteristics based on the existence of surface charges on an alumina insulator in vacuum. We changed the location and magnitude of surface charges and measured surface flashover voltage. From our experimental results, an attempt was made to clarify the influence of charges on alumina dielectrics on impulse surface flashover characteristics in vacuum. From this, we concluded that (1) when surface charges were located near the cathode electrode, a positive charge made the surface flashover voltage lower and a negative charge made the surface flashover voltage higher; and, (2) when surface charges were located in the way of the discharge path, both positive and negative charges made the surface flashover voltage lower. We were able to explain these results by considering the influence of surface charges on the electric field at flashover and on the secondary electron emission avalanche. [ABSTRACT FROM AUTHOR]

The electrical insulation reliability of solid spacers in Gas Insulated Switchgears (GISs) is an important issue to achieve a safe operation of such equipment. Among different phenomena, charge accumulation represents the most important matter that can degrade the overall performance of these insulation systems. For this respect, this paper discusses the contribution of partial discharge (PD) activity by ac voltage application to charge accumulation in the small gap at the electrode/epoxy interface as one of the weakest points in GIS solid spacers. The partial discharge inception voltages for non-accumulated charge case (PDIV0) and after exposing to PD activity (PDIVn) are measured among different gap lengths, simulating delamination at the electrode/epoxy interface. The PD activity is generated using applied voltage with 1.2 x PDIV0 for all gap lengths examined in this study (50~500 µm). In these measurements, PDIV increased with increasing the number of PD pulses as a result of accumulated charges. The accumulated surface charge density is estimated using the boundary equations and is compared for the different gap lengths. The accumulated charge density was larger for the smaller gap lengths. Comparing PD parameters with accumulated charge density enabled us to identify that the number of negative and positive PD pulses is the main parameter that corresponds to charge accumulation process. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the thermal runaway characteristics of a BSCCO HTS single pancake coil conduction-cooled with a 4 K-GM cryo-cooler system. We also evaluate the static and dynamic characteristics of the HTS coil by measuring the temporal evolution of the temperature and the voltage for steady current and the typical current patterns of the load fluctuation compensation at different ambient temperatures T0 in the range of 20-50 K. Moreover, we experimentally discuss the criterion for monitoring the conduction-cooled HTS SMES system during compensating operation for load fluctuations. [ABSTRACT FROM AUTHOR]

We have been developing Superconducting Fault Current Limiting Transformer (SFCLT) as a superconducting transformer with current limiting function. As the Step-5 of the SFCLT project for the up-graded ratings of current and voltage, in this paper, we focused on the up-grading of current by parallel-connected YBCO coated conductors. Based on the asymmetric configuration of coated conductors, different parallel connections were tested and evaluated in terms of critical current level and current limiting characteristics under large ac current at 77 K in liquid nitrogen. [ABSTRACT FROM AUTHOR]

The electrical insulation reliability of solid spacers in Gas Insulated Switchgears (GISs) is an important issue to achieve a safe operation of such equipment. Among different phenomena, charge accumulation represents the most important matter that can degrade the overall performance of these insulation systems. For this respect, this paper discusses the contribution of partial discharge (PD) activity by ac voltage application to charge accumulation in the small gap at the electrode/epoxy interface as one of the weakest points in GIS solid spacers. The partial discharge inception voltages for non-accumulated charge case (PDIV0) and after exposing to PD activity (PDIVn) are measured among different gap lengths, simulating delamination at the electrode/epoxy interface. The PD activity is generated using applied voltage with 1.2×PDIV0 for all gap lengths examined in this study (50∼500 μm). In these measurements, PDIV increased with increasing the number of PD pulses as a result of accumulated charges. The accumulated surface charge density is estimated using the boundary equations and is compared for the different gap lengths. The accumulated charge density was larger for the smaller gap lengths. Comparing PD parameters with accumulated charge density enabled us to identify that the number of negative and positive PD pulses is the main parameter that corresponds to charge accumulation process. [ABSTRACT FROM AUTHOR]

As the deregulation of the electric power industry moves forward, there is an increasing need for cost cutting and it is becoming exceedingly important to keep track of the residual life and identify the timing of replacement for power transmission equipment that has aged for several tens of years in the field. This paper, taking up the theme of "insulation degradation phenomena and lifetime evaluation for power transmission equipment", conducted cross-sectional comparison of different types of equipment although this kind of evaluation was made independently for these equipment types so far. This paper covered six types of equipment: gas insulated switchgear (GIS), gas insulated transformers, oil filled (OF) transformers, OF cables, crosslinked polyethylene (XLPE) cables, and power capacitors. As a result of examining the characteristics such as electric, thermal, mechanical, and hygroscopic degradations, each of these equipment types was found to have distinctive Voltage-time (V-t) and Voltage-number (V-N) characteristics, which sometimes greatly varied from those of others. Since thermal degradation is dominant for gas insulated transformers and oil filled transformers, their lifetimes depend on the reduction of mechanical strengths of Polyethylene Terephthalate (PET) or insulating paper. Therefore, it is effective to diagnose decomposition products such as CO, CO2 and furfural generated in the thermal degradation mechanism. On the other hand, the influence of electric degradation has more significant impact on the other equipment types except OF cables. Such GIS components as epoxy spacers, XLPE cables, and power capacitors for which long-term ac voltages are dominant, are commonly characterized by the long-term V-t characteristics with a large gradient (small n-value). In terms of insulation structures, there is a possibility of reducing the degree of degradation by improving solids or the interface between solids and electrodes. [ABSTRACT FROM AUTHOR]

This paper discusses partial discharge (PD) propagation, degradation and lifetime characteristics of magnet wires for inverter-fed motor under surge voltage application. Experimental results showed the time variation of PD activity, i.e. intermittent PD, successive PD, critical PD and breakdown (BD), under repetitive surge voltage application with a fixed peak value. Critical PD was a drastic change of PD activity and was identified as the partial BD of magnet wires. Since the final BD was confirmed to be always induced at the critical PD location, the critical PD was regarded as an important indicator to determine the lifetime of magnet wires. The experimental results also clarified that the lifetime of magnet wires could be determined by the total number of PD generation from its inception to breakdown. PD activity was interpreted by the time transition of PD generation frequency, and its mechanisms were discussed. [ABSTRACT FROM AUTHOR]