Research on the Long-distance Transmission

In view of the imbalanced distribution of power load and resources, including the status of “electric shortage” in some cities in our country, the article discusses the long-distance transmission technology. It mainly analyzed two ways of the long-distance transmission: UHV AC transmission and UHV DC transmission. The fractional frequency transmission technology and half wavelength AC transmission technology of AC transmission are introduced. Some key technologies of long-distance transmission are described. It has a guess for long-distance transmission future direction.

基于对称分量法的调相机定子故障特征分析

传统同步调相机定子绕组匝间短路故障机理分析方法通常认为电机定子电流接近三相对称,并以此为基础建立同步调相机故障电流的数学表征。但是,一旦发生定子绕组匝间短路故障,同步调相机三相定子电流的对称性将遭到破坏,使得传统故障机理分析方法所建立的数学表征无法准确反映电机内部电气量的变化。文中通过引入对称分量法,建立故障后同步调相机瞬时有功/无功功率的数学模型,提出利用瞬时有功/无功功率中的2次谐波进行定子绕组匝间短路故障诊断。仿真和实验的结果表明:相较于利用定子电流3次谐波与基波幅值之比诊断故障的传统方法,文中方法在轻微故障状态下能提高至少7倍的诊断灵敏度,更易完成早期故障诊断。同时,所提方法中的故障特征量不受同步调相机工况和故障位置的影响,具有强鲁棒性。

基于合成场强仪的输电工程地面合成电场研究

高压直流(DC)输电线路交叉跨越是我国特高压(UHV)技术发展中出现的问题。由于两回DC线路相互影响,交叉跨越区域内合成电场呈复杂的三维分布,UHV DC输电工程地面合成电场计算较为困难。选取典型±800 kV UHV DC输电工程进行地面合成电场的实测研究。参照GB 39220—2020,采用HDEM-01合成场强仪进行野外现场实测。测量参数为有效期内的场磨传感器上积聚的电荷量。测量结果与运行初期实测数据的对比结果表明:±800 kV换流站周边运行初期合成电场强度略低于后期,且整体水平较低;沿线电磁环境敏感目标运行初期、后期的实测数据中,74%的数值小于5 kV/m。通过此次研究,明确了UHV DC输电工程合成电场不同时期的特性。该研究有助于推进UHV DC输电工程的快速建成,并提高其运行安全性,从而推动电力工程建设的发展。

混合三端直流输电系统受端交流故障穿越协调控制策略

以乌东德电站送电广东广西特高压多端柔性直流示范工程为研究对象,考虑混合三端柔性直流输电系统因受端不同位置交流故障所致的直流过电压,提出相应的故障穿越协调控制策略。在受端主站发生网侧交流瞬时故障的情形下,通过设计混合型模块化多电平电压源换流器全桥子模块自适应负投入策略,实现了利用子模块电容短时过电压储能的能力来快速补偿站间直流电压的上升;短暂时延后,送端电网换相换流器通过定量调整电流指令值策略来减小子模块的不平衡充电功率。在受端主站发生阀侧交流故障的情形下,优先利用输电健全极的功率转代裕度来消纳故障极的部分不平衡功率;同时,故障极从站跟随主站半压运行,相应的高低压阀组切换至定电流及定电压模式,最终实现抑制站间过电流及减小盈余功率。仿真结果表明,2种故障条件下,所提的协调控制策略均可较快实现故障期间的功率平衡,有效抑制仅配备稳态基本协调控制策略下系统所出现的直流过电压现象,同时也基本维持了送端的总体有功传输容量。

Damping Characteristic Analysis and Optimization of Wind-thermal-bundled Power Transmission by LCC-HVDC Systems

With the rapid development of renewable energy,wind-thermal-bundled power transmission by line-commutated converter based high-voltage direct current(LCC-HVDC)systems has been widely developed.The dynamic interaction mechanisms among permanent magnet synchronous generators(PMSGs),synchronous generators(SGs),and LCC-HVDC system become complex.To deal with this issue,a path analysis method(PAM)is proposed to study the dynamic interaction mechanism,and the damping reconstruction is used to analyze the damping characteristic of the system.First,based on the modular modeling,linearized models for the PMSG subsystem,the LCC-HVDC subsystem,and the SG subsystem are established.Second,based on the closed-loop transfer function diagram of the system,the disturbance transfer path and coupling relationship among subsystems are analyzed by the PAM,and the damping characteristic analysis of the SG-dominated oscillation mode is studied based on the damping reconstruction.Compared with the PAM,the small-signal model of the system is obtained and eigenvalue analysis results are presented.Then,the effect of the control parameters on the damping characteristic is analyzed and the conclusions are verified by time-domain simulations.Finally,the penalty functions of the oscillation modes and decay modes are taken as the objective function,and an optimization strategy based on the Monte Carlo method is proposed to solve the parameter optimization problem.Numerical simulation results are presented to validate the effectiveness of the proposed strategy.

基于PMU的特高压直流输电系统孤岛运行控制方法

受特高压(Ultra-High Voltage,UHV)直流输电系统自身运行特点的影响,孤岛运行阶段的环流难以实现快速维稳,提出基于电源管理单元(Power Management Unit,PMU)的特高压直流输电系统孤岛运行控制方法。考虑输出电压的角度会受电压源换流器(Voltage Sourced Converters,VSC)的影响发生瞬时改变,提出有功-相角下垂控制方法,逆变器通过微型PMU的同步信号,确定派克变换的参考坐标系,将特高压直流输电系统孤岛运行阶段的目标维持频率作为控制基准。以调整特高压直流输电系统中所有分布式发电装置(Distributed Generation,DG)的相角参考值处于一致状态为导向,结合微型PMU测得的公共母线电压相角参数,控制有功补偿量。在测试结果中,环流达到0值后出现的偏离情况程度稳定在10.0 VA以内,并在测试后的0.8 s内达到0稳态。

±800 kV直流线路工程邻近带电体架线施工防护研究

考虑直流输电线路邻近带电体架线施工风险,利用表面电荷法得到导线表面电场强度数学模型,应用有限元计算了邻近±800 kV直流输电线路和T型塔的空间电场分布情况,给出了架线施工时邻近线路和T型塔的最小关注距离。研制了直流电场安全监控报警装置并用于验证有限元仿真结果;依托昌吉–古泉±1000 kV特高压直流工程甘3标段完成了装置功能验证,结合验证结果给出了邻近带电体施工管控措施。研究结果可为邻近带电体架线安全施工提供技术参考。

A DC Chopper Topology to Mitigate Commutation Failure of Line Commutated Converter Based High Voltage Direct Current Transmission

To reduce the probability of commutation failure(CF)of a line commutated converter based high-voltage direct current(LCC-HVDC)transmission,a DC chopper topology composed of power consumption sub-modules based on thyristor full-bridge module(TFB-PCSM)is proposed.Firstly,the mechanism of the proposed topology to mitigate CF is analyzed,and the working modes of TFB-PCSM in different operation states are introduced.Secondly,the coordinated control strategy between the proposed DC chopper and LCC-HVDC is designed,and the voltage-current stresses of the TFB-PCSMs are investigated.Finally,the ability to mitigate the CF issues and the fault recovery performance of LCC-HVDC system are studied in PSCAD/EMTDC.The results show that the probability of CF of LCC-HVDC is significantly reduced,and the performances of fault recovery are effectively improved by the proposed DC chopper.

特高压直流输电系统中送端LCC换流站的电压平衡控制策略

与高压直流输电相比,特高压直流输电拥有更高的电压等级,能够以更低的经济成本实现稳定、高效的大规模电力输送。该文针对特高压直流输电系统中送端换流站的高低压阀组所存在的电压不平衡问题,分析电压不平衡现象产生的机理,并提出一种基于电压变化量对换流阀组电流参考值进行动态修正的电压平衡控制策略。然后,基于PSCAD/EMTDC搭建特高压直流输电系统的电磁暂态仿真模型,通过在稳态时切除/投入电压平衡控制策略及送端功率阶跃和送端交流系统故障3种不同工况,观测系统的动态响应特性。结果表明,所提电压平衡控制策略简单有效,且在不同工况和不同交流系统强度下都具备较好的控制效果。

基于混合LSTM深度学习的特高压直流线路模量幅值比故障测距研究

对特高压直流(Ultra high voltage direct current,UHVDC)输电系统而言,准确可靠的测距方案可确保故障线路快速恢复、提高供电可靠性。提出一种基于线模分量和零模分量幅值比的特高压直流线路单端故障测距方法。首先推导出故障距离与初始电压行波模量幅值比之间的近似公式。公式表明,两者之间存在非线性关系,且与过渡电阻无关。然后选用混合长短期记忆(Long short-time memory,LSTM)深度学习网络进行训练和学习,提取各模量初始电压行波首波头的幅值比作为深度学习网络的输入量,以故障距离作为输出量,构建深度学习故障测距模型。搭建云广±800 kV特高压直流输电系统仿真模型。仿真实验表明,所提出的测距方法不受故障类型和过渡电阻的影响,且测距结果具有较高的准确性,相对误差不超过0.34%。

Single-end Protection Scheme Based on Transient Power Waveshape for Hybrid HVDC Transmission Lines

The recent in-depth development of hybrid highvoltage direct current(HVDC) transmission systems poses looming adaptability challenges to protection. The various and disparate direct current(DC) transmission topologies can profoundly affect the operating characteristics of DC transmission networks, which result in the lack of performance of conventional DC protection schemes in such topologies. This significantly limits the application of hybrid HVDC technologies. This paper proposes a single-end protection scheme based on the transient power waveshape for fast and sensitive detection and classification of different types of DC faults in hybrid HVDC transmission lines. The fault characteristics and their causes under different fault conditions are analyzed in detail with a pre-introduced linearized transient model of a hybrid HVDC transmission system, demonstrating that the formation of the fluctuation characteristics of local measurements is mainly determined by the buffering and absorption effects of lumped-parameter reactors on transient traveling-wave(TW) energy. Simulation results verify the sensitivity, rapidity, reliability, and anti-interference ability of the proposed scheme when applied to hybrid HVDC transmission lines. Furthermore, it is confirmed that the proposed scheme is adaptable to symmetric voltage-sourced converter(VSC) and conventional line-commutated converter(LCC) based HVDC transmission lines.

Phasor Analytical Model of Non-isolated DC/DC Converter Based on Modular Multilevel Converter for DC Transmission Grids

Non-isolated DC/DC converter based on modular multilevel converter(MMC)technology is expected to play an important role in future DC transmission grids.This paper presents a phasor analytical model for this new family of converters which is suitable for a range of studies like DC grid power flow or DC/DC parametric design.The 30th-order phasor model is derived in 3 coordinate frames:zero sequence(DC),fundamental frequency(dq),and double frequency(d2q2).The second-harmonic current suppression control is included as an option.Additionally,an estimation of the required control signals is presented,and a closed-loop model is developed which facilitates direct calculation of all variables and fast parametric studies.The accuracy of the proposed models is verified against a detailed PSCAD model for a wide range of parameters.The studies illustrate the importance of the second-harmonic components on the model accuracy.Finally,the impact of the converter parameters on the performance is studied,and a basic eigenvalue stability analysis is given.

特高压直流输电接地极中预制舱方案的应用设计

在特高压直流输电工程中,接地极作为一个重要的组成部分,直接影响特高压直流输电工程的可靠性。为了节约占地面积,减少施工周期,特高压直流输电接地极逐渐采用预制舱方案。根据接地极站址所处环境条件,为保证舱内元器件运行环境可靠稳定,提出了常规环境和重风沙环境下2种接地极预制舱典型布置方案,并从结构设计和辅助系统设计2个方面对接地极预制舱的主要设计要点进行了详细介绍。

面向特高压直流输电线路带电作业的直升机吊索法研究

为解决特高压直流输电线路导线数量多带电作业难的问题,文章提出了一种面向特高压直流输电线路带电作业的直升机吊索法。该方法可满足特高压线路带电作业要求,具有效率高、技术强和速度快的明显优势。结合湖北某特高压直流输电线路带电作业需求和设备缺陷,详细介绍了直升机吊索法技术应用的作业流程,通过现场带电作业实践,验证了直升机吊索法能够在保证作业人员安全的前提下,提高作业效率,具有适用性,对未来特高压直流输电线路带电作业的开展具有一定的参考价值。

特高压直流输电工程控制保护装置通信故障及处理研究

特高压直流输电工程是目前电力输电系统中的一项重要技术,其具有传输能量大、损耗小、占地面积少等优点。然而,在特高压直流输电过程中,控制保护装置通信故障是常见的问题,对于这些故障的及时处理是保证输电工程正常运行的关键。通过研究特高压直流输电工程控制保护装置通信故障产生的原因和处理方式,探讨如何增强特高压直流输电工程的稳定性和可靠性。

±800kV特高压直流输电线路的电位转移电流特性

为了确保±800kV特高压直流(UHVDC)输电线路带电作业过程中线路和作业人员的安全,对带电作业进入等电位过程中的电位转移电流特性进行研究有助于采取适当的防护措施。为此,采用光纤脉冲电流测量系统对进入±800kV特高压直流输电线路过程中的电位转移电流进行了测量,进入直流等电位过程中的电位转移电流脉冲最大幅值为149.98A,脉冲宽度为几十μs,正极性和负极性脉冲都存在。根据进入交直流线路等电位的特点,采用电磁分析软件研究了进入等电位过程中作业人员与极导线间的电位分布,计算了作业人员与极导线和杆塔等接地构件间的电容,根据这些参数建立了交直流线路进入等电位过程中的电位转移电流的分析模型,对特高压交流(UHVAC)与特高压直流线路的电位转移电流进行了计算。计算与测量结果表明特高压直流线路的电位转移电流远小于特高压交流线路,可以为特高压输电线路带电作业方法的选取提供参考。

基于经验小波变换的电晕电流降噪方法

随着电压等级升高和输电距离增加,在特高压直流输电线路上因电晕电流引起的电能损失和环境问题更加严重。深入分析电晕电流特性,对抑制电晕效应、实现长距离高效输电具有重要意义。电晕电流的复杂性导致时域和频域特性分析面临诸多困难,因此提出了基于经验小波变换的电晕电流降噪方法。首先,针对超长实测电晕电流数据,提出分段经验小波变换;其次,根据电晕电流的复杂频谱特性,提出了改进的频谱极大值搜索方法;最后,结合分段经验小波变换的分解结果,重构出了降噪后的电晕电流。实验结果表明,提出方法可以有效地抑制不同电压等级下实测电晕电流中的多种噪声成分,实现超长电晕数据的高效降噪处理,为电晕电流特性研究提供了崭新方法,为准确计算电能损失、探索电晕放电规律提供理论和技术支撑。

±800kV特高压直流输电线路单端电气量暂态保护

高压直流(high voltage direct current,HVDC)输电线路两端的平波电抗器和直流滤波器构成现实的边界元件,对暂态电压高频分量呈带阻传变特性,来自直流线路区外的高频电压信号通过平波电抗器和直流滤波器后被衰减,其能量显著减小,不同频带的高频电压信号小波能量可应用小波变换求得。利用区内、外故障时于保护安装处获得的暂态电压小波能量的显著差异来构造直流输电线路区内、外故障判据;利用故障暂态电压小波变换模极大值,构造启动判据;利用正极和负极暂态电压分别与+800和-800kV的相关系数,构造雷击干扰识别判据;利用两极线极波,构造故障选极判据。给出了特高压直流(ultra high voltage direct current,UHVDC)输电线路单端电气量暂态保护方案。对该保护进行了大量仿真分析,计及了雷击干扰、边界上避雷器动作、不同过渡电阻、换相失败故障等因素的影响。仿真结果表明,该保护具有绝对选择性,能可靠有效地保护直流线路全长。

基于先导发展法的特高压直流输电线路绕击特性分析

雷电绕击是影响高压输电线路安全稳定运行的关键因素之一,特高压直流线路对雷电防护的需求与常规线路相比更加迫切。为此介绍了基于先导发展法的特高压直流线路雷电绕击跳闸率分析方法;利用该方法针对±800 kV特高压直流线路绕击特性开展仿真研究,分析了绕击跳闸率随绝缘水平、保护角的变化规律,研究了典型地形条件下雷电绕击路径和绕击电流的分布特性,分析了山坡、山脊和跨谷地形条件下线路的绕击跳闸率,研究了线路极性对跳闸率的影响。研究表明,减小保护角可明显降低绕击跳闸率,在山坡地形条件下,外侧导线由于受屏蔽减弱更易受到雷击,雷电先导可从近似水平的方向击中导线;跨谷深度增加时,由于地面屏蔽作用减小,雷击跳闸率明显提高;理论分析和运行经验都表明,直流线路正极导线遭受雷击的概率远高于负极,线路位于山脊时雷电绕击基本发生在正极导线侧。