高压直流输电单极运行对土壤电阻率的影响(英文)

UHVDC transmission system is characterized by transferring large amount of electrical power over long distance , which plays an important role in the west-to-east power transmission project. Since the underground current can reach several kA under UHVDC monopole operation, the safe and stable operations of grounding electrode are highly relative with nearby soil resistivity. This paper introduces porous media model and analyzes the influence of rising temperature around grounding electrode on soil resistivity. Based on researching soil conduction mechanism under DC, calculation formula for soil resistivity and the rule of DC density on soil resistivity are presented. Furthermore, the relationship between DC density and soil resistivity is obtained, which was demonstrated by current characteristics experiment of soil resistivity.     

特高压直流与双回超高压交流同塔架设输电线路导线布置方式及换位方式分析(英文)

For AC and DC hybrid transmission lines,the arrangement and transposition modes of AC conductors not only affect the unbalance factor of AC lines,but also influence the bias current of DC converter transformers by AC and DC coupling.Excessive bias current will influence the normal operation of converter transformers,thus the optimal AC phase arrangement and transposition mode of hybrid lines was studied to minimize the coupling effect between AC and DC lines to fit the requirements on both aspects.Based on the parameters of the Ximeng-Shanghai project in China,a detailed simulation model of the DC converter station and the hybrid transmission line with double-circuit AC 500 kV transmission lines and DC ±800 kV transmission lines were presented in the software PSCAD-EMTDC,and the coupling effects of the hybrid transmission lines were elucidated.The fundamental frequency components of DC poles with different operation conditions,arrangements of conductors and operation modes were analyzed,and the effective arrangement and transposition limiting the fundamental frequency current component of the DC line were compared.Simulation results show that AC operating conditions can affect DC induced components while the DC system operation mode has no apparent effect.With compact arrangement and inconsistent transposition of AC lines,the fundamental frequency component on DC lines can be reduced effectively;the three-transposed mode within the hybrid line is the optimal layout scheme,considering both the requirements of DC bias current and AC unbalance degree.     

基于ATP-EMTP的±500kV直流线路雷击事故仿真分析(英文)

This paper calculates and researches on lightning accident of ±500 kV Xing-An DC transmission line in Guangdong based on ATP-EMTP and the simulation calculation model of the HVDC has been constructed. The results show that: when a lightning current strikes to the positive polar conductor of double circuit transmission line and the flashover of insulator strings occurs, as the over-voltage wave propagating along the lines due to the coupling effect between the conductors, the grounding electrode lines would produce the coupling voltage wave, which makes the flashover of the insulator strings occur at the different place along the grounding electrode lines, the unbalanced current of the grounding polar line is produced due to the insulator strings flashover and the unbalanced current exists for a long time, when the unbalanced current is up to the locking condition, the negative polar conductor is locked and the double-pole block fault occurs. In the paper, some effective measures are given to prevent this accident.     

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.     

海上风电直流传输网络的成本效益分析

Due to low load factors of wind power generation,it is possible to reduce transmission capacity to minimize the cost of transmission system construction.Two VSC-HVDC schemes for offshore wind farm,called the point to point(PTP) and DC mesh connections are compared in terms of the utilization of transmission system and its cost.A Weibull distribution is used for estimating offshore wind power generation,besides,the cross correlation between wind farms is considered.The wind energy curtailment is analyzed using the capacity output possibility table(COPT).The system power losses,costs of transmission investment and wind energy curtailment are also computed.A statistic model for the wind generation and transmission is built and simulated in MATLAB to validate the study.It is concluded that a DC mesh transmission can reduce the energy curtailment and power losses.Further benefit is achievable as the wind cross correlation between wind farms decreases.     

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.     

云南—广东±800KV特高压直流输电工程系统设计和研究(英文)

The ±800 kV ultra high voltage direct current(UHVDC) transmission system is an extraordinary challenge to system design and equipment manufacture.China Southern Power Grid Company(CSG) organized research and design for the construction of Yunnan-Guangdong ±800 kV UHVDC project(YG UHVDC project),and got large technical breakthroughs and advanced technologies for ±800 kV UHVDC transmission systems.These advanced technologies include power system stability,main electrical wiring,overvoltage and insulation coordination,external insulation,electromagnetic environment,control and protection,and arrangement of the main equipments.Meanwhile,CSG led the researches on specification of main equipments,such as converter valve,converter transformer,dry-type smooth reactor and others involved in the whole process management of equipment supervisions.The YG UHVDC project was put into commercial operation in 2010 as the first pilot ±800 kV UHVDC project in the world.The whole system operated in a stable and smooth manner,and the UHVDC equipment and control systems passed the test under the practical operation in CSG bulk power system,which shows that the design and research objectives were achieved.     

±800kV特高压直流输电系统换流站换流阀过电压机理和计算条件(英文)

The thyristor converter valve is the key equipment of commutation in ultra high voltage direct current(UHVDC) transmission systems.Owing to the limited voltage and current overload capacity,any transient overvoltage may cause permanent damage to the thyristor converter valve.In order to specify the converter valves’ overvoltage levels of the ±800 kV UHVDC transmission system,the mechanisms of its generation and development are discussed in detail,from which the calculation conditions for the highest stresses of the converter valves are given.Finally,the converter valve’s overvoltage of Xiluodu UHV converter station is simulated.The research results show that the overvoltages of the converter valves in the upper 3-pulse group of the high voltage(HV) and low voltage(LV) 12-pulse converter are generated jointly by the DC line voltage and the converter transformer’s voltage at its valve side.Calculation conditions for this overvoltage are: DC system in bipolar operation mode,converter station operating as rectifier,maximum DC system operating voltage,minimum DC current,minimum AC system voltage of the converter station.Furthermore,the other converter valves’ overvoltage is caused by the phase-to-phase switching surge generated at the converter station’s AC side,penetrating into the valve hall.Overall,the maximum overvoltages of Xiluodu converter station in the upper 3-pulse group of the HV and LV 12-pulse converter are 379.1 kV and 384.9 kV,for other converter valves the maximum overvoltage is 375.3 kV.     

influence of Qinghai-Tibet HVDC Transmission System on AC Transmission Line Protections in Qinghai Power System

To analyze the influence of _＋400 kV Q~nghai-Tibet HVDC transmission system on transmission- line protections in Qjnghai AG power system, a closed-loop simulation system was constructed by combing HyperSim system with HVDG control protection devices. Various faults on double-circuit 750 kV and multi- circuit 330 kV AC transmission lines in Qjnghai power system were simulated. The impedance characteristics and harmonic components at Qjnghai side of Qjng-Tibet DG transmission line were analyzed. The harmonic proportion in voltages and currents were studied for faults that took place at different locations near the DG system. The inflence of Qing-Tibet DG system on the directional components of protections, differential protections and distance protections of AC transmission lines was discussed and drew the conclusions that the DC sytem had little influence on differential protections, while had great inflence on directional components and distance protection. The conclusions can provide reference for studying the interaction between AC and DG systems.     

超高压交流线路对平行架设特高压直流线路的电磁感应

交流输电线路与特高压直流输电线路平行架设时,通过电磁耦合交流线路会在特高压直流线路上感应出工频交流分量。感应产生的工频电流,经过换流器后会产生直流分量。此直流分量流经换流变压器,会导致换流变压器偏磁。采用EMTDC程序建立了交／直流输电系统仿真模型,对交流输电线路对平行架设的特高压直流输电线路产生的电磁感应影响进行仿真研究,分析了交／直流线路平行架设长度、接近距离、土壤电阻率、杆塔接地电阻等因素对特高压直流线路的工频电磁感应影响。另外,对比分析了超高压紧凑型线路、常规型线路分别与特高压直流线路平行架设时特高压直流线路上的工频感应电压、电流和直流偏磁电流。     

特高压交流线路对平行架设特高压直流线路的工频电磁感应影响

特高压交流/直流输电线路平行架设可以提高走廊利用率。同时,特高压交流线路通过电磁耦合会在特高压直流线路上感应出工频交流分量。在直流线路上感应产生的工频电流分量,经过换流器后会产生直流分量。此直流分量流经换流变压器,导致换流变压器偏磁。采用EMTDC程序建立了特高压交/直流输电系统仿真模型,对交流输电线路对平行架设直流输电线路产生的电磁感应影响进行仿真研究,分析了特高压交/直流线路平行架设长度、接近距离、线路换位以及单相接地故障等因素对工频电磁感应的影响。另外,对比分析了特高压单、双回线路与特高压直流线路平行架设,特、超高压交流线路与特高压直流线路平行架设下特高压直流线路上的工频感应电压、电流和直流偏磁电流。     

交直流线路同塔输电对换流变直流偏磁的影响

华东地区输电线路走廊资源紧缺,为了充分利用架空线路走廊,将出现特高压直流线路与交流线路同塔架设的情况.根据规划的宁东-绍兴±800kV特高压直流主回路参数和华东地区交直流同塔线路数据,采用EMTDC建立了交直流输电系统的仿真模型.计算了交流线路输送功率、直流系统运行工况以及同塔段位置对直流线路工频感应分量的影响,给出了工频感应分量沿直流线路的分布规律.研究结果表明,由于直流线路上的工频感应分量与直流额定电压和电流相比很小,故对直流滤波器、平波电抗器和换流阀的参数选择影响不大,而工频感应分量所引起的换流变压器(简称换流变)阀侧直流偏磁电流则会对换流变正常运行产生一定程度的不利影响.最后,根据换流变可承受直流偏磁电流的能力,给出了可能的同塔架设的长度,并提出了限制直流偏磁电流的措施.     

交流线路对平行架设特高压直流线路的影响及限制措施

随着电力需求的不断增长以及输电线路走廊资源的紧缺,在一些地区可能出现特高压直流线路与交流线路平行架设或同走廊的情况。根据向家坝—上海南汇±800kV特高压直流主回路参数和规划的1 000 kV交流线路数据,采用EMTDC程序建立了特高压交/直流输电系统的仿真模型。计算了交/直流线路不同平行架设长度、不同接近距离下特高压直流线路上感应的工频电压、电流。研究了换流变阀侧直流偏磁电流与直流线路工频感应电流的关系,给出了换流变阀侧直流偏磁电流的计算结果。最后对交/直流线路的平行长度,它们之间的接近距离以及抑制换流变压器阀侧直流偏磁电流的措施提出了建议。     

特高压直流输电的地中电流对变压器的影响及其计算

特高压直流输电具有大容量、远距离输电等优点,在我国"西电东送"工程中起着重要的作用。针对特高压直流输电中对变压器的影响、对交流系统稳定性的影响和对地下金属的腐蚀等问题,笔者介绍了特高压直流输电系统单极运行产生的地中电流对变压器励磁电流的影响,建立了等效电路计算流过变压器的直流电流,讨论了几种缓解直流偏磁影响的方法。     

高压直流输电接地电极及相关问题综述

文中介绍了接地的基本概念,分析了入地电流、跨步电压、最大允许温升以及直流接地极寿命;指出在设计直流接地极时,应考虑土壤电阻率、接地极型式以及接地参数的计算等方面的问题;阐述了直流接地电流对变压器直流偏磁的影响,并提出了抑制措施,如采用深层接地技术,变压器交流出线串联电容器,在变压器中性点装设抑制直流电流的装置等;最后分析了高压直流输电系统的共用接地极模式.     

牛从直流翁源接地极入地电流对周边变压器直流偏磁的影响

根据牛从直流受端翁源接地极周边变电站情况,对牛从直流入地电流进行了实测和分析,并对牛从直流入地电流对周边交流变压器直流偏磁的影响进行了详细的仿真计算。结果表明,翁江站变压器220 k V侧中性点均不接地或装设隔直装置可减小流入交流系统的直流偏磁电流;翁江站110 k V供电片区优化接地方式,选择官渡、回龙站中性点接地,对交流系统直流偏磁的影响最小。     

±1100 kV古泉换流站接地极对变压器直流偏磁的影响

文中对±1100 kV古泉换流站接地极周边变压器及变电站地网进行了直流偏磁影响研究,根据周边交流电网中变压器的直流偏磁电流分布进行分析,建立相应的直流电阻网络耦合模型,并结合变压器直流偏磁的耐受电流限值,提出相应的变压器直流偏磁治理范围及直流偏磁治理方案,为华东地区的接地极选址提供参考。     

直流电位补偿法抑制变压器直流偏磁的研究

根据直流系统单极大地回线方式运行时变压器的直流偏磁原理,分析比较了现有几种抑制变压器直流偏磁的措施,运用直流电位补偿法原理进行了正、负电位补偿的模拟试验。试验表明直流电位补偿法能在一定程度上抵消系统单极运行流过变压器中性点的直流电流,抑制直流偏磁。且同等条件下正电位补偿电流的利用率大于负电位,但负电位补偿能对地网起到阴极保护作用。此外,还分析了补偿装置的布置及其对周边设施的影响,分析表明直流电位补偿法在现场实施中具有可操作性。     

土壤结构对直流入地电流分流特性的影响研究

高压直流输电系统单极大地回路运行时,从大地返回的直流电流通过接地网流入变压器中性点,从而引起变压器噪声增大、发热加剧等一系列不良后果。利用CDEGS软件对交直流互联系统进行建模仿真,直流输电系统以单极大地回线方式运行时,依据3种土壤分层结构分别计算了流经变压器中性点的直流电流量,得出了交流电网直流电流分布图。仿真结果表明:流经变压器中性点的直流电流因距离接地极的远近而变化,距离接地极越近,流经变压器中性点的直流电流量绝对值越大,近似呈对数函数形式分布;流经交流架空线路的直流电流值与土壤的分层结构、交流电网的拓扑结构以及距离直流接地极的远近相关。