共查询到20条相似文献,搜索用时 31 毫秒
1.
Seok B.Y. Komatsu H. Suehiro J. Hara M. Okamoto H. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2000,7(1):78-86
The partial breakdown (PBD) and complete breakdown (BD) phenomena in a composite insulation system of glass fiber reinforced plastic (GFRP) and liquid nitrogen are investigated to find the PBD and BD characteristics in high temperature superconducting (HTS) coils at quench. The electrode system used is made from a coaxial spiral coil-to-cylindrical electrode with an insulation barrier and spacers, and is immersed in liquid nitrogen. A heater is mounted inside the coil electrode to generate boiling which occurs on quenched superconducting coils. The experimental results show that (1) the polarity of PBD initiation under 60 Hz ac applied voltage depends on the width lc of the cooling channel, (2) PBD appears through a gas bubble locked between the coil and concentric insulation barrier due to the electrical gradient and the spacer, (3) breakdown voltages are affected severely by the risetime of the applied voltage and the current amplitude associated with PBD, (4) two kinds of BD mechanisms are found depending on the shape of the spacer, length of cooling channel and heater power 相似文献
2.
Seok B.Y. Tamuro N. Hara M. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1999,6(1):109-116
Bubble behavior is studied theoretically and experimentally with an electrode system which consists of concentric coil layer-to-cylindrical electrodes with insulation barrier and spacers immersed in liquid nitrogen for the simulation of the insulation environment in high temperature superconducting coils at the quenching state. The results show that bubble behavior is affected severely by 60 Hz electric field and pressure; it is categorized into two types according to the width lc of the cooling channel between coil layer and cylindrical electrode. When lc is larger than the diameter of bubble released from the coil electrode, bubbles rise by buoyancy at a low applied voltage, but they are trapped in grooves between coil-turns at higher applied voltages. Trapped bubbles move along the groove if there is no obstruction, but otherwise move out of the groove. When lc is smaller than the bubble diameter, the bubbles are trapped in the groove due to surface tension, and now along the groove even at no applied voltage. At higher applied voltages, the bubbles are trapped tightly and an electrohydrodynamic (EHD) instability is excited on the bubble surface if the spacer exists. Bubbles stream from the groove due to the effects of EHD instability and buoyancy 相似文献
3.
Hazeyama M. Kobayashi T. Hayakawa N. Honjo S. Masuda T. Okubo H. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2002,9(6):939-944
The partial discharge (PD) inception characteristics are studied in liquid nitrogen (LN/sub 2/)/polypropylene laminated paper (PPLP/sup /spl reg//) composite insulation system for high temperature superconducting (HTS) cable. Experimental results revealed that the magnitude of the initial PD increased as the PD inception electric field strength was increased, because the injected energy increased. Initial PD was generated at the first and third quadrant of applied AC voltage phase. The probability of initial PD at the positive and negative voltage phase was almost the same. The reason is because liquid nitrogen is a nonpolar molecule and we used symmetric electrode configuration with uniform electric field distribution. Finally, it was pointed out that PD inception electric field strength (PDIE) depended on the volume of the butt gap because of the increasing probability of weak points of electrical insulation, and PDIE linearly decreased with increasing stressed volume of the butt gap in the log-log scale. 相似文献
4.
Chigusa S. Maeda H. Taniguchi Y. Hayakawa N. Okubo H. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1999,6(3):385-392
We have been studying quench-induced `dynamic' breakdown characteristics of LHe and have already found that the electrical insulation performance of LHe was degraded drastically by the thermal bubble disturbance due to quench of superconductors. In this paper, in order to improve the insulation performance of LHe under quench conditions, we measured dynamic breakdown and prebreakdown characteristics of pressurized LHe. Experimental results revealed that breakdown voltage of LHe under quench conditions at 0.2 MPa was greatly improved, reaching 2 to 4× compared with that at atmospheric pressure under both uniform and non-uniform electric fields. Moreover, for practical and efficient insulation design of superconducting power apparatus, we investigated the dynamic breakdown voltage of LHe as functions of pressure and gap length 相似文献
5.
Okubo H. Hazeyama M. Hayakawa N. Honjo S. Masuda T. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2002,9(6):945-951
In this paper, we studied partial discharge (PD) inception characteristics and V-t characteristics of PD inception in liquid nitrogen (LN/sub 2/)/polypropylene laminated paper (PPLP/sup /spl reg//) composite insulation system for high temperature superconducting (HTS) cable. Experimental results revealed that the magnitude of initial PD was in the range of 2.0-30 pC irrespective of butt gap condition and the initial PD was generated at the first and third quadrant of voltage phase. PD inception electric field strength (PDIE) without butt gap was 5-10% higher than that with butt gap and thicker butt gap gave larger PDIE drop. Moreover, PDIE with butt gap depended on the butt gap thickness and the number of PPLP/sup /spl reg// layers. The reason is explained by the existing probability of weak points of electrical insulation at butt gap. Finally, lifetime indices n of V-t characteristics at PD inception were obtained as 80-100 irrespective of butt gap condition. These values showed enough flat characteristics of V-t phenomena of electrical insulation. 相似文献
6.
Hara M. Maeda Y. Nakagawa N. Suehiro J. Yamada S. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2006,13(3):470-476
This paper deals with the breakdown voltage characteristics of saturated liquid helium in the presence of a needle-shaped or spherical metallic particle to obtain insulation design data for pool-cooled, low-temperature superconducting coils and to find the predominant factor affecting the breakdown voltage of liquid helium at a given state. The results show the following. (1) The generation of bubbles at the instant of collision of a particle with an electrode is caused mainly by the kinetic energy released from the moving particle to the liquid helium, while the electrostatic energy accompanying the microdischarge between the particle and the electrode has a lesser effect on it. (2) The lowest breakdown voltage at different particle conditions appears in the case of a free needle particle. The low breakdown voltage is caused by the bubble triggered by the particle collision, the high electric field at the tip of the needle particle, and the rich initial electrons supplied by the microdischarge. 相似文献
7.
Okubo H. Hayakawa N. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2005,12(4):736-744
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 SF/sub 6/ gas and (3) liquid nitrogen/polypropylene laminated paper composite insulation system for high temperature superconducting cables are introduced and discussed. 相似文献
8.
Hiroshi Suzuki Toshihiro Takahashi Tatsuki Pokamoto Noboru Ishii Shin‐Ichi Mukoyama Akio Kimura 《Electrical Engineering in Japan》2008,164(2):25-36
A High‐Temperature Superconducting (HTS) cable has a bulk power transmission capacity as a candidate for the replacement of aged cables and/or for the increase of the power transmission capacity, and its diameter is preferred to be smaller than the inner diameter of the duct for the existing cables. To reduce the diameter of HTS cable, the cold dielectric (CD)‐type electrical insulation in which a cable core is immersed into liquid nitrogen (LN2) should be adopted, and the thickness of its electrical insulation layer has to be optimized. Since a partial discharge (PD) in the electrical insulation layer of the CD‐type HTS cable is considered as a major cause for the aging of the insulation layer, PD‐free design must be adopted for the CD‐type HTS cable. This paper describes a design method for the electrical insulation layer of the CD‐type HTS cable adopting the PD‐free design under AC stress, based on the experimental results such as a PD inception stress (PDIE), an impulse breakdown stress, and PD extinction characteristics under AC stress superimposed with an impulse stress. Moreover, the proposed design method was applied to a 500‐m HTS cable and was verified by a field test. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 25–36, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20512 相似文献
9.
Hara M. Miyama M. Satow T. Gerhold J. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1997,4(6):792-799
An insulation design procedure for SC (superconducting) coils for electric power apparatus is proposed and applied to a small scale SMES (superconducting magnetic energy storage system) consisting of two modules of pool-boiling helium-cooled SC coils. Coil operation parameters affecting insulation spaces are discussed on the basis of an estimated time-dependent ratio of insulation withstand voltage to induced voltage for different quenching states according to the proposed procedure 相似文献
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12.
Okubo H. Wakita M. Chigusa S. Hayakawa N. Hikita M. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1997,4(1):120-126
For practical insulation design of superconducting power apparatus, it is necessary to take into account an inherent phenomenon known as quench, the transition from the superconducting to the normal state. We investigated quench-induced dynamic breakdown and prebreakdown characteristics of liquid helium (LHe). Experimental results revealed that the quench of the superconductor drastically reduced the breakdown voltage of LHe in the thermal bubble disturbance. Moreover, dynamic breakdown characteristics in a quasi-uniform field using a superconducting coil were investigated. The results revealed that the breakdown was induced in the quench-initiated region where the largest thermal energy was generated 相似文献
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14.
Hara M. Nakagawa H. Shinohara T. Suehiro J. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2002,9(6):910-921
The paper deals with the bubble formation process in the presence of a free conducting particle in liquid helium to understand the electrical insulation environment in pool cooled superconducting devices under particle contaminated conditions. Experiments were conducted with DC stressed parallel plane electrodes containing a free spherical metallic particle of 1 mm radius in saturated normal and saturated superfluid helium. Experimental results show that a single bubble is always generated at the moment of particle collision with the electrode and the bubble behavior depends strongly on the state of the liquid helium. The bubble expanding and shrinking processes were analyzed on the basis of energy balance among released electrostatic and kinetic energies of the particle at the moment of particle collision with the electrode, kinetic energy of liquid driven by bubble growth, work done on environmental pressure and internal energy of the bubble gas. The analysis shows a fairly good agreement with experiments. 相似文献
15.
Suzuki H. Takahashi T. Okamoto T. Akita S. Ozawa Y. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2002,9(6):952-957
For the optimization of electrical insulation design for high temperature superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN/sub 2/ impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN/sub 2/ plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN/sub 2/ impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN/sub 2/ and cable model with short length with polypropylene laminated paper (PPLP/sup /spl reg//), Nomex/sup /spl reg// paper and cellulose paper. PD current pulse was found to have a steep rise time of /spl sim/ ns and amplitude of /spl sim/ tens /spl mu/A at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be /spl sim/ 5 mm under PD-free condition from viewpoint of long-term reliability. 相似文献
16.
研究了应用高温超导(HTS)线圈,通过L-C串联谐振电路从低压直流电源产生高电压的新方法。为了产生高电压,低压直流电源的极性需在电子开关的控制下每半个谐振周期切换一次。谐振电路中电阻的存在限制了它所能产生的高电压幅值。通过用HTS线圈制成的电感取代铜线圈电感,该电路所能产生的高电压的幅度会明显增大,在本文中,(Bi,Pb)2Sr2Ca2Cu3O10+x套银多股HTS线材被用来制造超导电感。虽然用此谐振方式产生的高电压不能给低阻抗负荷供电,但它可能用于电气设备局部放电测试或其他电气绝缘性能的检测等方面作为另一个应用该方法还可用于超导体自身电性能的测量。 相似文献
17.
This is a review to show the importance of electrical insulation in ac superconducting cables. An attractive superconducting cable has to be designed for the voltage range of 60-270 kV. Therefore, a reliable insulation design is imperative. Two types of insulation have been compared. One is composite insulation, namely laminar paper or plastic tape, impregnated with coolant. The other is solid insulation of extruded polymer on the conductor. The composite insulation has a lengthy history and, in the constructions to date, has been the insulation design used for superconducting cables. Some prototype superconducting cables with this type of insulation have been developed and successfully tested. However, the partial discharge in butt gaps may affect their long-term reliability. The solid insulation, on the other hand, can separate the coolant from the electrical insulation and can exploit the benefit of the super electrical insulation characteristics of polymers in the cryogenic region. Some attempts have been made to use this design with liquid nitrogen and liquid helium. One example incorporating extruded ethylenepropylene rubber (EPR) for insulation was found to satisfactorily go through the cool-down to a liquid helium temperature and to endure the simultaneous voltage and current tests. EPR, and possibly some other polymers, seem to be promising materials for solid insulation in the cryogenic region 相似文献
18.
The aim of this paper was to give an overview on partial discharges under oscillating impulse voltage.Three models(void in solid,needle-plate in air and oil) were presented,which describe the stochastic discharge process and represent internal discharges in solids and corona in air or silicon oil.Moreover,an air cored Rogowski coil and a sampling resistor for partial discharge(PD) measurement were developed and introduced in this paper.PD inception and extinction voltages(PDIV,PDEV) under single oscillating impulse voltage and AC voltage were investigated with different test samples.Experimental results firstly revealed that the PD inception voltage(PDIV) decreased with increasing applied voltage;secondly the PD inception voltage for three different insulating materials,showed an escalating trend with increasing frequency of the applied voltage.It was proven that the characteristics of PD under oscillating impulse voltage were identical to the features under AC voltage,which could be measured with the phase resolved partial discharge analysis(PRPDA) technique.Based on the reorganization and analysis of PDs under oscillating impulse voltage,the information about insulation defects was extracted from the measured data and used for estimating the risk of insulation failure of the equipment. 相似文献
19.
Naoki Hayakawa Masato Morikawa Hitoshi Okubo 《Dielectrics and Electrical Insulation, IEEE Transactions on》2007,14(1):39-45
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 相似文献
20.
Hayakawa N. Kobayashi T. Hazeyama M. Takahashi T. Yasuda K. Okubo H. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2005,12(1):166-174
Partial discharge (PD) inception characteristics of liquid nitrogen (LN2)/polypropylene (PP) laminated paper composite insulation system for high temperature superconducting (HTS) cables were investigated in terms of the volume effect and the V-t characteristics. The electrical and optical measurements of PD inception characteristics showed that initial PD could be generated between PP laminated paper layers, as well as in a butt gap. Using a parameter called statistically stressed liquid volume (SSLV) based on the discharge probability in both butt gaps and LN2-filled thin layers between PP laminated papers, we could systematically analyze and evaluate the volume effect on PD inception stress (PDIE). Furthermore, experimental results revealed that n values of V-t characteristics at PD inception were as high as 80-110. On the other hand, the lower n values obtained at breakdown were interpreted by the intensified PD development in thermal bubbles generated after the PD inception 相似文献