Research on Total Electric Field Prediction Method of Ultra-High Voltage Direct Current Transmission Line Based on Stacking Algorithm

Ultra-high voltage(UHV)transmission lines are an important part of China’s power grid and are often surrounded by a complex electromagnetic environment.The ground total electric field is considered a main electromagnetic environment indicator of UHV transmission lines and is currently employed for reliable long-term operation of the power grid.Yet,the accurate prediction of the ground total electric field remains a technical challenge.In this work,we collected the total electric field data from the Ningdong-Zhejiang±800 kV UHVDC transmission project,as of the Ling Shao line,and perform an outlier analysis of the total electric field data.We show that the Local Outlier Factor(LOF)elimination algorithm has a small average difference and overcomes the performance of Density-Based Spatial Clustering of Applications with Noise(DBSCAN)and Isolated Forest elimination algorithms.Moreover,the Stacking algorithm has been found to have superior prediction accuracy than a variety of similar prediction algorithms,including the traditional finite element.The low prediction error of the Stacking algorithm highlights the superior ability to accurately forecast the ground total electric field of UHVDC transmission lines.

A Novel Pilot Protection for VSC-HVDC Transmission Lines Based on Correlation Analysis

The control system of voltage source converter HVDC (VSC-HVDC) is complex and its fault tolerance ability is not sufficient, and correct rate of line protection device is not high. A novel pilot protection for VSC-HVDC transmission lines based on correlation analysis is proposed in this paper. In the principle, external fault is equivalent to a positive capacitance model, so the correlation coefficient of the current and voltage derivative is 1;while the internal fault is equivalent to a negative capacitance model, so the correlation coefficient of the current and voltage derivative is -1. Internal faults and external faults can be distinguished by judging the correlation coefficient. Theoretical analysis and PSCAD simulation experiments show that the new principle, which is simple, not affected by transition resistance, control type and line distributed capacitance current, can identify internal faults and external faults reliably and rapidly, having certain practical value.

DC steady-states analysis of lossy uniform transmission lines

A method for computing DC steady-state solutions in complex frequency-domain is put forward. It starts with complex frequency-domain transmission line equations, obtains the complex expressions of voltage and current at zero initial states, and find the DC steady-state solutions of voltage and current by using the fina value theorem of Laplace transform thory. The solutions are discussed with special internal resistances of DC voltage source and loads. A case study demonstrated that the proposed method is applicable to acquiring the DC steady-state voltage waveform and current waveform without first obtaining the analytic solutions.

Upgrading of Ge-Hu DC transmission line completed

On March 10, being the fir st in the world, the 500-kV double-circuit DC transmission line—GE—Hu upgrading project formally passed completion-acceptance, and

Traveling Wave Characteristics Based Pilot Protection Scheme for Hybrid Cascaded HVDC Transmission Line

The hybrid cascaded high-voltage direct current(HVDC)transmission system has various operation modes,and some operation modes have sharply increasing requirements for protection rapidity,while the traditional pilot differential protection(PDP)has poor rapidity,and even refuses to operate when faults occur on the DC line.Therefore,a novel pilot protection scheme based on traveling wave characteristics is proposed.First,the adaptability of the traditional PDP applied in engineering is analyzed for different operation modes.Then,the expressions of the forward traveling wave(FTW)and backward traveling wave(BTW)on the rectifier side and the inverter side are derived for different fault locations.From the theoretical derivation,the difference between the BTW and FTW on the rectifier side is less than zero,and the same is true on the inverter side.However,in the event of an external fault of DC line,the difference between the BTW and FTW at nearfault terminal protection installation point is greater than zero.Therefore,by summing over the product of the difference between BTW and FTW of the rectifier side and that of the inverter side,the fault identification criterion is constructed.The simulation results show that the proposed pilot protection scheme can quickly and reliably identify the short-circuit faults of DC line in different operation modes.

Scheme for realizing quantum computation and quantum information transfer with superconducting qubits coupling to a 1D transmission line resonator

This paper proposes a simple scheme for realizing one-qubit and two-qubit quantum gates as well as multiqubit entanglement based on de-SQUID charge qubits through the control of their coupling to a 1D transmission line resonator （TLR）. The TLR behaves effectively as a quantum data-bus mode of a harmonic oscillator, which has several practical advantages including strong coupling strength, reproducibility, immunity to 1/f noise, and suppressed spontaneous emission. In this protocol, the data-bus does not need to stay adiabatically in its ground state, which results in not only fast quantum operation, hut also high-fidelity quantum information processing. Also, it elaborates the transfer process with the 1D transmission line.

Fault location of untransposed double-circuit transmission lines based on an improved Karrenbauer matrix and the QPSO algorithm

Some double-circuit transmission lines are untransposed,which results in complex coupling relations between the parameters of the transmission lines.If the traditional modal transformation matrix is directly used to decouple the parameters,it can lead to large errors in the decoupled modal parameter,errors which will be amplified in the fault location equation.Consequently,it makes the fault location results of the untransposed double-circuit transmission lines less accurate.Therefore,a new modal transformation method is needed to decou-ple the parameter matrix of untransposed double-circuit transmission lines and realize the fault location according to the decoupled modal parameter.By improving the basis of the Karrenbauer matrix,a modal transformation matrix suitable for decoupling parameters of untransposed double-circuit transmission lines is obtained.To address the dif-ficulties in solving the fault location equation of untransposed double-circuit transmission lines,a new fault location method based on an improved Karrenbauer matrix and the quantum-behaved particle swarm optimization(QPSO)algorithm is proposed.Firstly,the line parameter matrix is decomposed into identical and inverse sequence compo-nents using the identical-inverse sequence component transformation.The Karrenbauer matrix is then transformed to obtain the improved Karrenbauer matrix for untransposed double-circuit transmission lines and applied to identi-cal and inverse sequence components to solve the decoupled modal parameter.Secondly,based on the principle that voltage magnitudes at both ends are equal,the fault location equation is expressed using sequence compo-nents at each end,and the QPSO algorithm is introduced to solve the equation.Finally,the feasibility and accuracy of the proposed method are verified by PSCAD simulation.The simulation results fully demonstrate that the innova-tive improvement on the basis of the traditional modal transformation matrix in this paper can realize the modal transformation of the complex coupling parameters of the untransposed double-circuit transmission lines.It causes almost no errors in the decoupling process.The QPSO algorithm can also solve the fault location equation more accu-rately.The new fault location method can realize the accurate fault location of untransposed double-circuit transmis-sion lines.

基于FSC和TCSC混合复用的交直流混联线路潜供电弧特性

为提高系统运行稳定性,高补偿度串补装置广泛投入使用,但线路故障后潜供电流存在高幅值的低频分量,潜供电弧难以自熄。针对此问题,基于交直流混联输电线路,研究了不同布置方式下串补度对潜供电流与恢复电压幅值影响,提出了一种固定串补(fixed series compensation,FSC)和可控串补(thyristor controlled series compensation,TCSC)混合复用抑制潜供电弧的方法。此外,为满足线路对高补偿度的需求,设计FSC和TCSC混合复用串补度最佳配置方案。结果表明,交直流混联线路采用串补度40%的双平台分散布置方式,潜供电流与恢复电压幅值达到最小,燃弧时间最短。高补偿度串补线路TCSC采用串补度10%、20%的配置方案更利于熄弧,提高重合闸成功率。

基于初始电流行波相位的多端混合直流线路单端保护方案

为了解决LCC-MMC型多端混合直流系统线路保护存在的问题,提出一种基于初始电流行波相位的多端混合直流线路单端保护方案。首先基于多端混合直流输电线路发生不同位置和类型的故障工况,推导直流线路入射电压行波的解析式并计算其高频段相位。其次结合线路边界行波折反射原理和测量波阻抗特性,提出利用初始电压行波相位的区内外识别判据,并根据雷击和短路故障的入射行波低频相位特性构建雷击干扰判据。在PSCAD/EMTDC中搭建昆柳龙多端混合直流系统模型进行验证,证明所提方案仅利用单端量信息即可满足故障判断和选线要求,满足速度性的同时具备一定的抗过渡电阻能力(500Ω)。

Statistical Analysis of Radio Interference of 1000 kV UHV AC Double-circuit Transmission Lines in Foul Weather

Analyzing the impact of radio interference(RI)variation during foul weather conditions is an area that has received limited study.This paper provides a statistical analysis of RI measurements obtained from a long-term observation station close to the world’s first commercially operating 1000 kV UHV AC double-circuit transmission line in China.During six months of observations,the impact of RI was studied on the line during fog,drizzle,and light snow and rain.It was found that RI increases linearly with the natural logarithm of the precipitation intensity.The Levenberg-Marquardt algorithm(LMA)is employed to fit the RI value with the precipitation intensity.The reasonable distribution of RI in different foul weather is verified by one-sample K-S test.This test is seen as beneficial for further RI prediction based on statistical weather mode.

CSC-HVDC输电线路单端行波自动故障定位方法

传统行波故障定位方法有行波波头难以识别,无法实现自动化的固有缺点,为此,基于直流线路发生故障时,线路两侧的直流滤波器和平波电抗器组成的物理边界会对电压行波中的高频信号产生全反射,而且高频电压行波在故障点折射强于反射的特点,采用线路的分布参数模型,提出了一种高压直流输电线路单端行波自动故障定位方法。该方法用线路高频电压分量和高频电流分量计算沿线电压分布,识别出前行波和反行波的最强叠加点即可实现故障定位。此方法避免了传统行波测距中需要人工识别行波波头的缺点,所需数据窗短,测距特征明显易于实现自动化,仿真验证表明该方法定位精度高,1 000 km线路最大测距误差仅为800 m,且不受过渡电阻的影响。

考虑直流控制系统影响的HVDC输电线路后备保护研究

在考虑直流控制系统影响的情况下,详细分析了HVDC输电线路区内、区外的故障特征以及直流控制系统的动作特性和控制状态。引入并分析了基于开关函数的交直流系统二次谐波计算等值模型。通过分析故障期间换流器触发角和直流侧二次谐波量的变化特征,提出了一种新的以换流器触发角为保护动作量,利用二次谐波分量闭锁的直流线路后备保护方案,给出了保护整定的理论计算方法。与直流线路纵联差动保护相比,该保护不因直流电流波动影响而被闭锁,保护动作时间较快;与微分欠压保护相比,具有更高的抗过渡电阻能力。通过PSCAD/EMTDC大量仿真计算,验证了该保护能可靠区分直流线路区内、区外故障,与直流线路纵联差动保护和微分欠压保护相比具有明显的优越性。

输电线路单导线覆冰形状对直流大电流融冰时间的影响

直流大电流融冰是输电线路冰灾防御的有效手段。根据实际运行条件下输电线路单导线覆冰形状在导线各处不一的情况,计算分析单导线圆形覆冰和翼形覆冰的直流大电流融冰时间。计算结果表明,翼形冰融冰时间仅为圆形冰融冰时间的10%左右。在重庆大学雪峰山能源装备安全国家野外观测研究站对LGJ—300/50和LGJ—400/35两种型号单导线进行直流大电流融冰实验。实验结果表明:LGJ—300/50导线翼形冰融冰时间为圆形冰融冰时间的10.6%,LGJ—400/35导线翼形冰融冰时间为圆形冰融冰时间的8.3%。基于此,该文提出抑制导线形成圆形冰促使其生长为翼形冰可降低直流大电流融冰时间,减少融冰能量消耗。

基于行波解析分析的柔性直流输电线路故障智能检测方法

故障数据匮乏是制约数据驱动故障检测方法应用的重要原因,为解决这一问题,提出一种基于行波解析分析的柔直输电线路故障智能检测方法。根据行波表达式生成训练样本,有效表达区内、外故障行波具有的主要特征。通过构造多层感知器(multi-layer perception,MLP)模型建立该行波特征与故障位置之间的映射关系,进而输出故障检测结果。最后,在PSCAD/EMTDC中搭建双端柔直系统模型,生成仿真样本,对训练后的智能检测模型进行测试。结果表明:该方法不依赖于大量历史故障数据,基于行波解析表达式这一继电保护领域知识提取行波特征,即可准确识别直流线路的区内外故障,并且具有较强的耐受过渡电阻能力,为解决传统模型受制于历史故障数据问题提供了一种可行思路。

利用模量模型识别的VSC-HVDC输电线路纵联保护新原理

电压源换流器型高压直流(VSC-HVDC)输电控制系统复杂,故障承受能力差,线路保护装置动作正确率不高。文中提出了一种利用模量模型识别的VSC-HVDC输电线路纵联保护新原理。该原理将区外故障等效为正的电容模型,差动电流和差动电压导数相关系数为1;将区内故障等效为负的电容模型,差动电流和差动电压导数相关系数为-1。通过判别相关系数的正负,即可区分区内、区外故障。在实际运行中,VSC-HVDC输电系统多为双极运行,为降低极间电磁耦合的影响,采用了1模和0模量构成判据。理论分析和PSCAD仿真实验表明,新原理无需补偿输电线路电容电流,原理简单、易于整定,不受过渡电阻和控制特性的影响,在各种工况下均能快速可靠地区分区内、区外故障。

基于MMC的两端TWBS-HVDC直流侧短路故障电流计算方法

基于三线双极结构的高压直流(TWBS-HVDC)输电系统能够较大程度地发挥直流线路的输电能力,是一种实现交改直和线路增容改造的有效方式。针对TWBS-HVDC系统与双极直流系统在接线形式上的差异,文中提出了一种适用于两端TWBS-HVDC的直流侧短路故障电流计算方法。首先基于模块化多电平换流器(MMC)暂态等效电路建立两端TWBS-HVDC在不同直流侧故障发生至线路直流断路器动作阶段的暂态等效模型。以暂态等效电路中独立回路数和动态元件阶数为标准,将所有直流故障归纳为3类,分析推导各类故障下的状态方程,通过求解状态方程中系数矩阵的特征值和特征向量得到故障电流解析表达式。最后在MATLAB/Simulink数字仿真平台中,搭建两端TWBS-HVDC模型进行仿真验证,结果验证了所提TWBS-HVDC直流侧短路故障状态方程求解法的准确性和有效性,为直流断路器选型和限流电抗器参数整定提供了可靠依据。

基于T区中低频衰减特性构成方向元件的特高压三端混合直流输电线路单端方向保护研究

将保护装置安装在T区两侧,基于T区中低频衰减特性构成方向元件,提出一种特高压三端混合直流输电线路单端方向保护方法。分析特高压三端混合直流输电系统整流侧、T区以及线路末端逆变侧三端边界频率特性,发现T区边界对故障电流暂态信号中低频分量有一定的衰减作用、整流侧边界和线路末端逆变侧边界对故障电流暂态信号高频分量有明显衰减作用。利用小波分解,根据T区两侧线路暂态电流中低频能量差判断故障方向,并提出故障方向判据。当T区左侧发生故障时,利用线路L1末端所检测到的高频暂态电流能量与低频暂态电流能量的比值来判别整流侧区内、外故障;当T区右侧发生故障时,利用线路L2首端所检测到的高频暂态电流能量与低频暂态电流能量的比值来判别线路末端逆变侧区内、外故障;T区发生故障时,判定为线路区外故障。给出基于T区中低频衰减特性构成方向元件的特高压三端混合直流输电线路单端方向保护方案,最后在PSCAD/EMTDC仿真平台搭建昆柳龙特高压三端混合直流输电系统模型并对所提保护方法进行验证,仿真表明该文所提保护方法能实现特高压三端混合直流输电线路全线速动保护。