基于脉冲电压法的10kVXLPE电缆绝缘诊断非线性分析(英文)

The diagnosis of water trees of cable insulation is of great importance as the water-treeing is a primary cause of aging breakdown for the middle voltage cables. In this paper, it is described how the water-tree-aged 10 kV XLPE cables were diagnosed. The cables were subjected to electrical stress of 5.9 kV/mm and a thermal load cycle in a curved water-filled tube for 3, 6 and 12 months of aging in accor- dance with the accelerated water-tree test method. The aged cables were used as the samples for water-tree diagnosis. First, the water-tree degraded cable, was charged by a DC voltage, and then the cable was grounded while a pulse voltage was applied to it for releasing the space charge trapped in the water trees. The amount of the space charge, which corresponds to the deterioration degree of the water trees, was calculated. The effects of DC voltage amplitude, pulse voltage repetition rate and aging conditions on the amount of the space charge were studied. Obtained results show that the amount of the space charge has a positive correlation with the applied DC voltage and the ag- ing time of the cables, and that a peak value of space charge appears with the increase of the pulse voltage repetition rate. An optimum pulse voltage repetition rate under which the space charge can be released rapidly is obtained. Furthermore, the releasing mechanism of space charge by the pulse voltage is discussed. Accumulated results show that the presented method has a high resolution for the diagnosis of water tree degradation degree and is expected to be applied in practice in future.     

计算高压直流输电线路等效干扰电流的一般性方法(英文)

As a critical part in the DC filter design,it is very important to quickly and correctly calculate the equivalent disturbing current.A general method for calculating the equivalent disturbing current of high voltage direct current(HVDC) transmission lines is proposed.In this approach,one 12-pulse converter was represented by four 3-pulse harmonic voltage sources in series,the DC network was described by a multi-phase coupled transmission line model,and the harmonic currents of certain frequency were solved based on the basic nodal analysis method.The multi-phase coupled transmission line model was described briefly,which could treat DC transmission lines of any structure,e.g.one or two DC circuits in a tower.The harmonic voltage source calculation steps were outlined,the steps to form the nodal admittance matrix were discussed,and the equations to calculate the equivalent disturbing current of the DC line were given.To verify the general applicability of the suggested approach,two different HVDC projects were studied:a traditional single circuit HVDC project,and a newly constructed HVDC project with double circuits on a same tower.The results show that the proposed method can calculate the equivalent disturbing current of the above two projects effectively,and has obvious advantages such as easy implementation,fast calculation and wide applicability.According to the two cases,the distributions of the equivalent disturbing currents along the line have the same trend,i.e.,the maximum value of the equivalent disturbing currents appears at the line inlet of both sides.Plus there is no fixed relationship between the equivalent disturbing currents and the HVDC line structures,because the equivalent disturbing current depends on many factors,such as background harmonics and converter transformer parameters.     

A NOVEL CONTROL STRATEGY FOR HIGH POWER HIGH-PERFORMANCE AC POWER SUPPLIES

摘要:The performances of the conventional currentregulated voltagecontrolled system with bipolar PWM are first analyzed in detail, then a novel control scheme suitable for highpower highperformance AC power supplies is present in this paper, which incorporates dual synchronous PWM technique of singlephase fullbridge inverter and multiple feedback loop. With this scheme, the output voltage of AC power supply can maintain highquality sine wave at low switching frequency and small output LC filter parameters. Moreover, it has excellent voltage regulation performance, fast dynamic response, good disturbance rejection, high nonlinear load compatibility, and small voltage modulation value. The validity of the proposed control scheme has been verified on a singlephase 30 kVA experimental prototype.     

电晕放电脉冲电流波形和相位分布的测量、分析与仿真(英文)

Partial discharge(PD) is one of the most important phenomenon in high voltage insulations.In most cases, the appearance of partial discharges is related to insulation defects.Understanding partial discharges is important for diagnosis on insulation condition.Corona discharges appear when extremely high electric field appears on the conductor surface exceeding the electric field strength of the gas.The high electric field may occur at around protrusion with very sharp tip.This paper reported a holistic approach of corona discharge investigation.The needle-plane electrode system was used.The medium between the electrodes was air.The needle was made from steel with radius of curvature of 3μm(Ogura needle).Sinusoidal as well as triangular applied voltages were used.The waveform of the corona discharges was measured using a digital oscilloscope.The corona discharge pulses were measured using a phase-resolved PD measurement system.The system was able to measure the magnitude(q) and phase angle position(φ) of each PD pulses,as well as the number of discharge pulses(n).The role of applied voltage was investigated using phase-resolved analysis of corona discharge pulses through pulse sequence,pulse magnitude and pulse number analysis. Experimental results indicated that corona discharge current waveform was an impulse with rise time of about several ns and the impulse width of about 100 ns.The Fast Fourier Transform analysis indicated that the corona discharge current waveform had several spectrum peaks at frequency of 7.8 MHz,85.9 MHz,109.4 MHz and 195.3 MHz.The experimental results also showed that discharge pulses were concentrated around the peak of applied voltage for both sinusoidal and triangular voltages.The discharge magnitude,as well as its probability of occurrence,was strongly dependent on the instantaneous applied voltage.The shape ofφ-n,as well asφ-q-n PD patterns,were strongly reflected by the shape of applied voltage.In order to get deep understanding of the corona discharge,by utilizing results of the phase-resolved analysis,electrical equivalent circuits of corona discharges were proposed.The electrical equivalent circuit contained capacitances and a spark gap.For deeply understanding of PD phenomenon,computer simulation was done by using the proposed electrical equivalent circuits.The similarity of the measured and simulated PD patterns was assessed by comparing measured and simulated theφ-q-n andφ-n PD patterns.The results indicated that simulated PD patterns similar to those obtained from experiment.     

电压响应方法在电力变压器状态评估中的应用(英文)

Power transformer is one of the most important equipment in the power system.Its operating condition affects the reliability of power supply directly.Therefore,in order to guarantee transformer operation safely and reliably,it is necessary to assess condition of power transformer accurately.Return voltage method based on voltage response measurements is still a new non-intrusive diagnosis method for internal insulation aging of transformer.In this paper the technique and application of return voltage measurement and some results of voltage response measurements of several transformers was introduced.Voltage response measurements were performed on various transformers with different voltage grades,various operating periods,different moisture contents and aging degrees on site.Derived moisture contents from return voltage measurement were compared with the corresponding moisture contents obtained from the analysis of oil samples.Based on on-site experiments and theoretical analysis,the criteria for insulation state of transformer are proposed.Moisture condition of transformer insulation can be determined by using return dominant time constant,and a good correlation between aging degree and the return voltage initial slopes of the aged transformers.Field test performed on several transformers,its interpretation of results are also presented,which proves that return voltage measurements can be used as a reliable tool for evaluating moisture content in transformer insulation.     

基于支持向量机的配电网过电压模式识别(英文)

The internal and external overvoltage in distribution networks is the main reason of accidents. Based on overvoltage data in distribution network recorded by overvoltage on-line monitoring system, this paper analyzes the characteristics of zero sequence voltage waveform. The maximum amplitude and RMS value of zero sequence voltage, the minimum RMS of low frequency component of three phase voltage in stable range and other five parameters are selected as characteristic parameters to identify internal and external overvoltage. According to the operation data and record, all overvoltage data recorded by on-line monitoring system were labeled as internal or external overvoltage and the discrimination function is constructed by support vector machine method. The test results of field acquired overvoltage data indicate that the identification parameters and method based on the zero sequence voltage and support vector machine (SVM) are correct and effective.     

高海拔地区±800kV特高压直流线路复合绝缘子悬挂方式对污闪电压的影响(英文)

To solve the contamination flashover problem for transmission lines in high-altitudes area,an analysis of the flashover performance of contaminated ±800 kV ultra high voltage(UHV) DC composite insulators of various suspension modes at a high altitude(2 100 m) is presented.The 50% withstand voltage(U50%) was determined by the up-and-down method.Experimental results show that suspension modes play an important role in the flashover performance since DC arcs detach from the insulator surfaces more easily at high altitudes than at sea level.Flashover voltages of the long string composite insulators gradually decreased with salt deposit density(SDD).The flashover voltage of type II string is by 4.6% lower than that of type I string.For type V string,the ionized air could more easily diffuse away from the insulator surface,while producing a higher utilization ratio of the leakage distance.Therefore the flashover voltage of type V string is by 8.7%～14.4% higher than that of type I string.Type Y string configuration appears to lead to much lower flashover voltages than type I and V string configurations.     

锦屏—苏南±800kV特高压直流输电工程换流站过电压及绝缘配合(英文)

Regarding to the problems of equipments manufacturing and layout in Jinping-Sunan ±800 kV UHVDC transmission system,overvoltage protection and insulation coordination in converter stations were studied.Configuration of arresters was studied at first,and scheme of MH arresters and V arresters connected in series was used to protect the high voltage Yy transformer’s valve side of dual 12-pulse converters.Overvoltage caused by DC faults and the withstand level of equipment in converter stations were studied using electromagnetic transient simulation.Based on operation parameters and characteristics of AC and DC system,equivalent models of both systems were set,together with most of the equipment in converter stations which would influence simulation results.The AC arresters’ transient response to AC faults was also simulated.For the most severe case,the peak voltage on AC bus arresters is up to 752 kV,along with stresses about 12.0 MJ in energy and 12.4 kA in current.Simulation results of transient overvoltage in converter stations were used to verify insulation coordination by comparing with the design value.The maximum insulation level would be less than 1 600 kV,which is no more than that in former UHVDC projects.     

Study on the Online Mode ol Micro-Grid

Smooth switchover of micro-grid from parallel operation mode to island operation mode is a significant method to guarantee the continuous power supply to important loads. This paper puts forward an online work mode on the basis of analyzing the features of parallel operation mode and island operation mode. According to the features of online work mode, the paper gives a fixed and unfixed DC bus voltage control strategy and builds the simulation model of unfixed DC bus voltage control strategy based on Matlab/ Simulink. The simulation results show that online work mode based on the unfixed DC bus voltage control strategy can avoid the unstable problem caused by handoff process between parallel mode and island mode, ensure uninterrupted power supply for important loads, and achieve maximum power tracking of photovoltaic power generation, in addition to reducing the complexity and cost of the system.     

25kV高精度直流负高压源设计

介绍了一种用于工业分析的高精度直流负高压电源,电源输出电压25 kV,最大输出电流100 mA。电源通过BOOST电路校正功率因数和调节电压,用移相全桥把直流电逆变成高频方波,然后经高频变压器升压后倍压整流得到直流高压。用特殊材料和工艺设计制作的高频高压变压器解决了分布参数影响和绝缘耐压等难题,满足了高频高压和大功率输出的需要。实验运行表明:该装置输入功率因数高、输出电压稳定、纹波系数小。     

一种适用于直流配电网的双向稳压型电压平衡器

直流配电网是一种新型供电系统,面对三线制直流配电网中负荷不平衡问题及其需为用户端提供稳定可靠供电的要求,提出一种适用于新型直流配电网的双向稳压型电压平衡器。将双向稳压Buck/Boost电压转换电路运用于电压平衡器之中,这样不仅能解决三线制网络中正负极电压平衡的问题,而且可以实现平衡输出端电压波动,维持输出端的电压稳定。首先针对该双向稳压型电压平衡器进行数学建模分析,利用状态平均法建立小信号状态模型;之后基于所提出的平衡器特性与其建模分析,在双向互补脉冲宽度调制（pulse width modulation,PWM）控制技术的基础上提出并分析控制策略;最后利用PSCAD仿真软件进行存在电压波动与不平衡负荷情况下的2种负荷类型的稳压平衡器仿真验证,仿真结果验证了其稳压及平衡电压能力,说明了理论分析的正确性。     

适用于MMC多端高压直流系统的精确电压裕度控制

当多端高压直流输电系统用于远距离输电时,直流线路的电压降落以及线路功率损耗会对电压裕度控制的精度带来较大影响,使直流电压不能稳定控制于一点,为此提出一种适用于多端柔性直流输电系统的精确电压裕度控制方法。推导了多端柔性直流输电系统的dq坐标数学模型,基于直流系统潮流计算的思想,充分考虑线路压降和损耗对控制参考值的影响,对电压裕度的取值进行计算,并在控制器中实现裕度修正。在PSCAD/EMTDC环境中建立了基于模块化多电平换流器的三端直流系统仿真模型,仿真结果验证了所提出的控制方法的正确性和有效性,该方法能够有效避免因电压裕度取值不当造成的控制特性偏移,并在系统受到较大功率扰动时可以有效、迅速地转换控制方式,提升系统稳定性。     

关于低压馈电开关漏电保护的探讨

介绍一种新型低压馈电开关保护器装置,通过对零序电压及零序电流的相位关系来定性确定是本回路或是其他回路发生漏电,利用附加直流原理来定量确定绝缘电阻值是否降低到动作规定值,具有功率方向型选择性判断、其精确度高,可靠性好,适宜煤矿井下供电。     

微功耗直流稳压器

微功耗直流稳压器采用电压切割和电压补偿的方法,实现了对直流电压的稳定或调整,该直流稳压器最大特点是,主电路不采用PWM脉宽调制,不产生EMI干扰,因此功耗极小而寿命极长,输出直流电压调整率高,效率高达99.5%,安全可靠,节能环保,电路简单,制作安装容易,其成本、体积、重量、功耗都是传统直流稳压器的十分之一。     

双输出罗氏变换器--先进的电压举升技术

通常在计算机外围电路及工业应用中需要镜象对称双输出电压。双输出ＤＣ－ＤＣ变换器能将正输入电源电压变换成正和负输出电压,由两个通道构成。由于寄生因素的影响。ＤＣ－ＤＣ变换器的输出电压及传输效率被限制。电压举升技术是电子电路设计中的一种常用方法,经长期研究它已成功地用于ＤＣ－ＤＣ变换器,像单输出（正或负输出）罗氏变换器一样,只用一个主开关的双输出罗氏变换器是一种新的基于先进电压举升技术的ＤＣ－ＤＣ升压     

高压交联电缆现场交流耐压试验

分析了直流耐压试验对交联聚乙烯电缆存在的缺点和问题 ,通过比较 ,选择了变频谐振装置在山东电网开展高压交联电缆的现场交流耐压试验 ,并介绍了交流耐压实例     

航空高压无刷直流电动机控制系统研究

针对今后飞机将会采用高压直流供电的趋势,研制了一种新型航空270V无刷直流电动机控制系统。文中提出了一种高稳定性的脉冲串转速给定方法,研究了基于专用单片开关电源控制芯片的DC/DC转换技术,系统采用单片机为控制核心,通过软、硬件相结合的方式,实现了无刷直流电动机的软起动、闭环稳速和转速连续调控。     

380kV／10mA直流高压电源的研制

介绍了一种用于离子注入机的380kV直流高压电源的电路原理及实现方法。基于高压电源在电压变得越来越高时会由于电场分布不均匀等问题容易导致电源自身的放电打火等问题,提出了一种更为优化的高压倍压方案。     

便携式智能直流高压发生器的研制

介绍了一台便携式智能直流高压发生器,其功率部分采用开关电源技术和倍压整流技术,控制部分采用单片机(MCU)和CPLD结合的结构,测量部分采用AD采样单片机处理的方法。整个装置实现了便携化、数字化和智能化。目前,该装置运行可靠。