高压SF6自能膨胀式断路器开断小容性电流的数值模拟与介质恢复强度分析

用质量守恒方程、动量守恒方程和能量守恒方程以及Laplace方程分别描述了灭弧室内气流场和电场,用有限元方法数值模拟高压SF6自能膨胀式断路器开断小容性电流的过程,分析了其灭弧室内气流场和电场的变化规律,并根据流注理论,计算并分析了弧后介质恢复强度.结果表明,电场强度最高处位于静弧触头头部的表面附近,动静弧触头间的滞止区,使介质恢复强度上升;主喷口与喉部之间超声速流,使介质恢复强度下降.     

高压断路器辅助开关分断能力研究及结构优化设计

对FK-口型辅助开关灭孤室进行二维数学建模,分析其内部电场强度分布,推导出电流过零后介质击穿的判断条件,对灭弧室结构进行优化,达到降低电场强度,使电场分布趋于均匀的目的,为辅助开关的优化设计提供了有效的解决方法.     

The irreversibility of dielectric strength of vacuum interruptersafter short-circuit current interruption

The irreversibility of dielectric strength of commercial vacuum interrupters after a large number of consecutive short-circuit current interruptions is investigated in order to find out how dielectric performance of a vacuum interrupter degrades during its service life. Breakdown voltage data were measured in appropriate experiments in which the types of tested interrupters and arcing conditions were varied. It was found that for interrupters with poor contact material the dielectric strength can deteriorate severely, falling below limits required by standards. It is concluded that the most important for the irreversible decrease in the dielectric strength is the contact material, i.e. its erosion properties. It appears that contacts with axial magnetic field are less susceptible to irreversible changes in dielectric strength after short-circuit current interruption than contacts with transverse magnetic field     

Analysis of the electric field and force in an arrangement of a conducting sphere and a plane electrode with a dielectric barrier

This paper presents an analysis of the electric field and dielectrophoretic force in an arrangement consisting of an uncharged conducting sphere and a plane electrode with a dielectric barrier. The electric field is calculated by using the method of multipole images using an iterative algorithm proposed for calculating the images of the dielectric barrier of finite thickness. The calculation results show electric field intensification due to the presence of the dielectric barrier having higher permittivity, /spl epsiv//sub S/, than that of the surrounding medium, /spl epsiv//sub E/; however, if the barrier is separated from the conducting sphere by at least the sphere radius, its influence is negligible. Inside the dielectric barrier, the electric field on the axis of symmetry becomes more uniform and the average field significantly increases with decreasing its thickness. For a case where dielectric barrier is sufficiently thin, the electric field at the contact point and the force on the conducting sphere vary approximately as power functions of /spl epsiv//sub S///spl epsiv//sub E/.     

Effects of hot SF/sub 6/ on post-arc circuit breaker design

SF/sub 6/ is blown through the arc during interruption of an SF/sub 6/ puffer circuit breaker. This hot gas flows down an exhaust tube into the chamber of a dead tank circuit breaker where it can lower the dielectric withstand between the exhaust tube and the tank of the circuit breaker, leading to dielectric breakdown during the transient recovery voltage after clearing. This paper presents experimental evidence that any such breakdown is controlled by the hot gas near the exhaust tube, with cold gas in the remainder of gap having little effect on the breakdown voltage. This experimental conclusion is supported by a detailed theory for conditions under which breakdown can occur.     

特高压直流母线MOA的电位与电场分布计算

分析了恒定电场的计算方法;根据特高压直流母线避雷器的结构,建立三维有限元模型,计算了其在直流持续运行电压下的电位电场分布;结果表明,在直流电压下,避雷器电阻片上承担相同的电压,防晕环的主要作用是降低局部产生过高场强和防止电晕;同时对该避雷器的防晕环进行了结构优化。     

THDF125/67型发电机定子绕组环形引线直流耐压放电分析及处理

针对某THDF125/67型1000MW汽轮发电机定子绕组直流耐压试验放电问题,经过多次直流耐压试验,发现是定子绕组环形引线放电。分析放电原因是环形引线裸露的接地紫铜片没有涂刷环氧胶黏剂导致电场分布不均匀,裸露紫铜片位置的电场强度过高,当电场强度达到空气的击穿场强时,裸露紫铜片发生沿面放电。拆除玻璃纤维带,对裸露紫铜片彻底涂刷环氧胶黏剂后,发电机泄漏电流和直流耐压试验通过。最后对环形引线运行接地线的安装工序提出建议,以防止同类放电故障的发生。     

SF_6断路器开断能力数值预测方法研究综述

综述了SF6断路器极限开断能力以及介质开断能力的数值预测方法的最新研究进展。电流过零前200 ns的电弧电导(G200)是判断断路器热开断能力的一个重要参数,为计算G200,对电弧特性进行模拟,在燃弧阶段采用磁流体动力学模型,而在接近电流零区采用Mayr模型,从而建立相应的电路模型来确定电弧时间常数和电弧功率损耗系数等参数,以分析高压断路器的热开断能力。为判断电击穿能力,需要根据电弧过零时灭弧室内的每一点的压力和温度值,确定对应点的临界击穿场强分布Ec,同时计算在暂态恢复电压作用下灭弧室内的电场分布Ea,然后通过比较灭弧室内各处Ea和Ec的值,就可以判断出灭弧室内不同区域电击穿几率的大小。     

252kV自能SF_6断路器开断能力的研究和提高

提高电力系统元件的可靠性是提高电力系统可靠性的重要措施。笔者主要从优化断口间的绝缘结构、改善介质状况和增强热膨胀效应方面来提高断路器的开断能力。所研究的252 kV断路器总体设计方案采用双室+双动的自能式灭弧室结构和触头运动方式,并结合定型产品的设计经验进行了关键结构参数的设计优化:确定热膨胀室和压气室的容积及其配合问题,保证了大电流开断的可行性;利用电场分析软件,对断路器的关键部位的电场强度进行了计算、分析和优化;为了抑制由电弧引起的气体密度的下降,加强热气体的排放效率,进行了导气流通道的改进,改善了介质状况。所研制的断路器通过全部型式试验,并已投入生产,同时为后续产品的研发提供了技术平台。     

Application of 800-kV SF6 dead tank circuit breaker with transmission line surge arrester to control switching transient overvoltages

An 800-kV metal oxide transmission line surge arrester (TLA) has been developed, installed and tested on the AEP 765-kV Marysville-Kammer transmission line. The purpose of this TLA is to pave the way for the development, construction and application of an 800-kV SF/sub 6/ dead tank circuit breaker without closing resistors and free standing current transformers at American Electric Power's (AEP) 800-kV Orange station. Eight hundred kilovolts is the maximum design operating voltage, and 765 kV is the nominal operating voltage. Successful field test results of the TLAs ability to limit switching overvoltages emanating from circuit breaker operation to below the transmission line switching withstand are given. In addition, successful test results of the 800-kV dead tank circuit breaker design dielectric test are given in this paper.     

新型强迫换流型限流断路器真空介质强度的恢复特性

为了保证新型强迫换流型真空直流限流断路器关断短路电流的可靠性,对该型断路器分断过程的真空介质恢复特性进行研究。设计了与断路器关断过程等效的介质恢复试验方案,通过等效试验结果和理论推演公式的拟合,得到了新型强迫换流型限流断路器真空灭弧室触头打开过程的动态介质强度恢复规律。研究结果表明:减小燃弧能量、提高触头运动速度可提高真空灭弧室介质的临界击穿电压;综合考虑燃弧时间与燃弧能量及触头开距的关系,随着燃弧时间的增加,真空灭弧室临界击穿电压先减小后增大。所得介质恢复规律可以作为新型断路器优化设计的参考依据。     

SF6自能膨胀式断路器开断大电流过程的数值模拟与分析

在建立喷口电弧与喷口烧蚀蒸气相互作用的数学模型基础上,应用有限元方法数值模拟了SF6自能膨胀式断路器开断大电流的过程,计算并分析介质恢复过程.研究结果表明:膨胀室内压力的建立与燃弧过程密切相关,第二个电流半波的燃弧过程,对压力的影响较第一个电弧电流半波的大,是压力建立的关键过程.电流过零后灭弧室气流特性主要为:由于膨胀室内气流的作用,喷口喉部内形成一滞止区,弧隙间的温度迅速下降,喷口下游气流逐渐发展成超音速流.介质强度恢复特性表现为迅速上升的过程,而后为缓慢上升的过程;开断电流减小,介质强度恢复的速度快,介质强度高.     

Condensed metal vapor on alumina ceramic in vacuum interrupters

Investigations have been carried out on the dielectric performance of the ceramic (high-purity alumina, Al/sub 2/O/sub 3/) surface in vacuum interrupters after switching. In order to examine the influence of the shielding on the protection of the ceramic surface against metal vapor condensation different types of vacuum interrupters (VIs) have been tested: VIs with and without shielding. Additionally, two contact materials CuCr: 75:25 wt% and WCAg: 56:4:40 wt% have been investigated to compare the adhesion of different metal vapors to alumina ceramic surfaces. After having performed a HV conditioning of the VIs, dc arcs with arbitrary arcing times were triggered between the contacts simulating the generation of metal vapor during high current interruption and load break switching. Between the arcing tests the insulation levels of all VIs have been tested by means of HV ac source. Afterwards the VIs were opened and the microstructure of the metallic condensate on the inner ceramic surface was analyzed by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The integral chemical composition of the metallic film was investigated by inductive coupled plasma (ICP).     

Induction charging of granular materials in an electric field

It is well known that particles can be freely levitated in an electric field due to the charge induced on the particles by the external field. The charge depends upon the electric field strength and particle properties. This paper studies some of these factors to investigate the fundamentals of induction charging for granular materials. An experimental apparatus was set up to collect the levitated particles in a filter contained in a Faraday pail and the charge-to-mass (Q/M) ratio was obtained based on the charge and mass measurements for the samples in the filter. Furthermore, the particle size distribution was measured and analyzed by laser diffraction and microscopy and the surface mean diameter (D/sub s/) and volume mean diameter (D/sub v/) were obtained. In these experiments irregular shaped Al/sub 2/O/sub 3/ particles and spherical glass beads with a size range of 42-390 /spl mu/m were used and tested at different electric field strengths. By combining the results of Q/M, D/sub s/ and D/sub v/, the charge per particle was calculated and the results compared with theoretical values. It was confirmed that the particle charge is dependent upon the electric field strength and the particle properties of size, shape, density, resistivity, and adhesive force.     

Intentionally inserted oxygen depleted (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ layers as a model of DC-electrical degradation

The relative dielectric constant versus voltage (/spl epsiv//sub r/-V) characteristics and the current density versus electric field (J-E) characteristics of (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ films, which have intentionally inserted oxygen depleted layers near the bottom electrodes, were investigated as a model of dc-electrical degradation phenomena. Our investigation demonstrated that the intentionally inserted oxygen depleted layer is the cause of the tunneling conduction.     

±320kV直流电缆交联聚乙烯/三元乙丙橡胶附件击穿特性

高压直流电缆接头与终端为电缆系统故障的多发点,其击穿强度为直流输电系统安全稳定运行的重要基础。文中以±320 kV高压直流海底电缆中交联聚乙烯(cross linked polyethylene,XLPE)/三元乙丙橡胶(ethylene propylene diene monomer,EPDM)附件为研究对象。首先,研究电缆及附件负荷循环耐压试验,发现附件界面为击穿薄弱环节;其次,研究绝缘材料电导率随温度变化特性对电场分布的影响规律,通过有限元仿真模拟电缆空载和满载运行时附件的温度分布与电场分布,发现最大电场出现在电缆绝缘靠近附件应力锥一侧,为29.5 kV/mm,低于附件材料的击穿场强;最后,研究界面在直流电场下空间电荷特性对电场分布规律的影响,通过电声脉冲法测试复合叠层片状样品介质界面的空间电荷及其电场分布,发现场强畸变率约为100%~200%。同材料本征绝缘匹配相比,界面空间电荷积聚对附件内部电场造成的畸变程度更严重,在后续附件提升中应更注重开发抑制空间电荷的绝缘材料。     

不同运行方式下特高压直流输电线路的地面电场与离子流分布

以向家坝—上海±800 kV特高压直流输电线路工程为背景,针对特高压直流输电线路可能存在的4种运行方式,计算和分析了上述输电线路下方地面电场与离子流密度的分布情况,研究了工程投运后特高压直流输电线路产生的电磁环境问题。结果表明：在双极运行方式下,地面场强与离子流密度均满足标准要求;并联导线带有相同极性的高电压,同性排斥作用既加强了地面电场强度,又增加了离子流密度,因此单极–双导线并联大地回线运行方式下的地面场强与离子流密度最大,应在实际工程中尽量避免采取这种运行方式。     

Improved Performance of Stair-Stepping Buffer-Gate 4H Silicon Carbide Metal Semiconductor Field Effect Transistor

Abstract

The 4H SiliconCarbide metal semiconductor field effect transistor (4H-SiC MESFET) with a buffer layer between the gate and channel (BG) is optimized and a new stair-stepping buffer-gate structure (SBG) is proposed for improving the breakdown characteristics. The terminal technology of breakdown point transfer (BPT) is applied in 4H-SiC SBG-MESFET in order to scatter the electric field lines and transfer the breakdown point. The breakdown mechanism is further investigated by simulating the surface electric field distribution and electrostatic potential contours. The results show that the breakdown voltage is increased from 120?V to 180?V, improved by the rate of 50% while the current density has hardly deteriorated, and thus the current density is improved from 9.35?W/mm to 13.2?W/mm in comparison with BG structure.     

Rated overload Characteristics of IGBTs for low-voltage and high-voltage devices

By a vertical shrink of the nonpunchthrough insulated gate bipolar transistor (NPT IGBT) to a structure with a thin n-base and a low-doped field stop layer a new IGBT can be realized with drastically reduced overall losses. In particular, the combination of the field stop concept with the trench transistor cell results in an almost ideal carrier concentration for a device with minimum on-state voltage and lowest switching losses. This concept has been developed for IGBTs and diodes from 600 V up to 6.5 kV. While the tradeoff behavior (on-state voltage V/sub CEsat/ or V/sub F/ to tail charge) and the overall ruggedness (short circuit, positive temperature coefficient in V/sub CEsat/, temperature independence in tail charge, etc.) is independent of voltage and current ratings the switching characteristics of the lower voltage parts (blocking voltage V/sub Br/<2 kV) is different in handling to the high-voltage transistors (V/sub Br/>2kV). With the HE-EMCON diode and the new field stop NPT IGBT up to 1700 V there is almost no limitation in the switching behavior, however, there are some considerations-a certain value in the external gate resistor has to be taken. High-voltage parts usually have lower current density compared to low-voltage transistors so that the "dynamic" electrical field strength is more critical in high-voltage diodes and IGBTs.     

触头盒内最大电场强度的计算

建立了舌形触头盒内最大电场强度的计算公式。公式表明触头盒的介电常数愈大,盒内触头最大电场强度愈小,公式计算结果与实测相当接近,可供舌形触头盒绝缘结构设计参考。