NEW PRINCIPLE FOR DIRECTIONAL COMPARISON CARRIER PROTECTION OF EHV TRANSMISSION LINES

The increasing scale and complexity of power systems require high performance and high reliability of power system protection.Protective relaying based on directional comparison with power line carrier or microwave channels is the most suitable protection scheme for long distance EHV transmission lines and is widely used in power systems.The key element of such protection is a directional relay used to discriminate the fault direction.In order to overcome the disadvantages of conventional directional relays,the authors of this paper put forward the directional comparison carrier protection based on the artificial neural network(ANN).The protection is extensively tested using electromagnetic transient program (EMTP) under various electric power system operating and fault conditions.It is proved that the directional comparison carrier protection based on ANN,which can recognize various fault patterns of the protected transmission line(such as fault direction,fault phases etc.)correctly in any kind of operating and fault conditions and the whole process,is satisfactory for EHV transmission line protection.

Overvoltage Suppression for UHV Transmission Lines

The overvoltage phenomena of ultra high voltage (UHV) transmission lines are analyzed and verified by EMTDC/PSCAD simulation. Referring to the theoretical analyses and operating experiences of extra high voltage (EHV) transmission lines in China and UHV transmission lines in Russia and Japan, the methods to suppress the internal overvoltage in UHV transmission lines by protection and control strategies are discussed. Through the cooperation among the recloser, shunt reactor, tripping and closing resistance, and metal oxide varistor(MOV), the overvoltage can be restrained within an acceptable level.

Measurement and Simulation of Induced Voltage and Current on 110 KV Crossing Transmission Lines under UHV AC Transmission Lines

The induced electricity of 110 kV transmission lines which cross the UHV AC transmission lines may threaten personal safety of the maintenance staff. In this paper, field measurement of the induced voltage and induced current on a 110 kV crossing line inside Jinhua in Zhejiang province is performed. The electrostatic induced voltage on the measured line is 12.24 kV. The power frequency electromagnetic field simulation model is established, and the calculation results are consistent with the measured. Influence factors analysis shows that the electrostatic induced voltage on the 110 kV line is 12.78 kV, the electromagnetic induced voltage is 12.3 V, the induced current through ground wire is less than 1A when the UHV lines operate at full load. The induced voltage and current decrease while the crossing distance increases. Parallel lines induction is much higher than crossing lines. The electromagnetic induced voltage after ground knife-switch shut down would exceed the human safety voltage 36 V while the crossing angle is less than 30?, so the temporary ground wire must be hanged to ensure safety of the maintenance staff.

Effects of Un-transposed UHV Transmission Line on Fault Analysis of Power Systems

The conventional fault analysis method based on symmetrical components supposes that the three-phase parameters of un-transposed transmission line are symmetrical in case of fault. The errors caused by the method with the symmetrical distributed parameter circuit model as the equivalent circuit of the un-transposed ultra high voltage(UHV) transmission line were studied under both normal operation and fault,and the corresponding problems arising were pointed out. By contrast with electromagnetic transient and power electronics(EMTPE) simulation results with the asymmetrical distributed parameter circuit model of un-transposed line, it is shown that the conventional method cannot show the existence of negative and zero sequences before fault happening and there are many errors on voltage and current after fault happening which are different with fault types. The error ranges of voltage and current are 2.13%-81.13% and -7.82%- -86.15%, respectively.

Modeling of Lightning Shielding Failure in UHV Transmission Line Based on Randomness Theory

The operation data obtained abroad indicates that shielding failure in UHV transmission lines mostly accounts for the tripping-out accidents introduced by lightning striking the transmission line.Based on the discharge theories of long air gap and randomness theory,a leader progression model of lightning shielding failure is presented in this paper.The random characteristics of the downward and upward leader are simulated in this model.The ground slope angel is also considered in this model by using coordinate transformation.Moreover,the system voltage is also taken into consideration in this model.The simulation results show that the good agreement between this model and the field data.And the results suggest that return striking exist obviously in UHV transmission line.

Digital simulation studies on long transmission line protection based on balance of energy

The protection based balance of energy is a new technique specially proposed for long transmission lines. This technique depends upon the calculation of net energy into the transmission line by two independent methods and comparing them to indicate healthy and faulty conditions. In order to study the performance and feasibility of the protection based on balance of energy, the new protection has been extensively tested by using EMTP on a long transmission line with various configurations and operating conditions (including single pole line, double circuit lines and two phase operation). The results calculated by EMTP show that under any condition of a power system, the proposed technique has excellent performance,the viability even for high resistance ground faults and a short operation time.

Research on the Anti-corona Coating of the Power Transmission Line Conductor

An anti-corona method for the power transmission lines is proposed in this paper. The RTV coating is used as the anti-corona coating, which is spaying onto the surface of the wearing conductor. The corona characteristic of the conductor test was done, and the corona onset voltage increase after the spraying of the anti-corona layer, the corona loss in the same voltage decrease, which could prove the excellent effect of improving the corona characteristic of the conductor. This anti-corona method will have great prospect, based on the background of the construction of UHV power transmission lines.

基于序电流相位差的EHV/UHV输电线路高阻抗故障选相研究

为了实现超高压和特高压输电线路的故障快速诊断,将序电流相位差技术应用到输电线路高阻抗故障选相中。开展了三相网络单相接地故障和相间接地故障分析,通过零序和负序电流分量相位差对故障相区间进行了划分,建立了序电流相位差、相阻抗、相间阻抗、3段距离继电器保护范围与故障类型、故障相别的关系;提出了一种以序电流相位差为判断依据的超高压和特高压输电线路高阻抗故障选相新方法;在500 kV,400 km的输电线路上对该故障选相方案的精确性及可靠性进行了评价,并进行了RTDS仿真测试。研究结果表明:该故障选相方案能够实现精确可靠的识别,并有足够的边际应对意外因素或计算误差,即使在电网振荡时,也可以实现可靠的系统故障相识别。

A review of single phase adaptive auto-reclosing schemes for EHV transmission lines

Statistics shows that transients produced by lightning or momentary links with external objects, have produced more than 80% of faults in overhead lines. Reclosing of circuit breaker (CB) after a pre-defined dead time is very common however reclosing onto permanent faults may damage the power system stability and aggravate severe damage to the system. Thus, adaptive single-phase auto-reclosing (ASPAR) based on investigating existing electrical signals has fascinated engineers and researchers. An ASPAR blocks CB reclosing onto permanent faults and allows reclosing permission once secondary arc is quenched. To address the subject, there have been many ASPARs techniques proposed based on the features trapped in a faulty phase. This paper presents a critical survey of adaptive auto-reclosing schemes that have hitherto been applied to EHV transmission lines.

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.

Fault component integrated impedance-based pilot protection scheme for EHV/UHV transmission line with thyristor controlled series capacitor(TCSC) and controllable shunt reactor(CSR)

This paper analyzes the fundamental frequency impedance presents a novel transmission line pilot protection scheme characteristic of a thyristor controlled series capacitor （TCSC） and based on fault component integrated impedance （FCII） calculated for a transmission line with TCSC and controllable shunt reactor （CSR）. The FCII is defined as the ratio of the sum of the fault component voltage phasors of a transmission line with TCSC and CSR to the sum of the fault component current phasors where all the phasors are determined at both line＇s terminals. It can be used to distinguish internal faults occurring on the line from external ones. If the fault is an external one the FCII reflects the line＇s capacitive impedance and has large value. If the fault is an internal one on the line the FCII reflects the impedance of the equivalent system and the line and is relatively small. The new pilot protection scheme can be easily set and has the fault phase selection ability and also it is not affected by the capacitive current and the fault transition resistance. It is not sensitive to compensation level and dynamics of TCSC and CSR. The effectiveness of the new scheme is validated against data obtained in ATP simulations and Northwest China 750 kV Project.

Effect of Different Arresters on Switching Overvoltages in UHV Transmission Lines

The amplitude of switching overvoltages is a key factor for designing the insulation of UHV equipment. The effect of different arresters needs to be studied, since installing arresters is an important way to suppress switching overvoltages in UHV transmission lines. Switching overvoltages on the 1000 kV Huainan-Huxi double-circuit transmission line were simulated for different operating modes and different arrester designs using the electromagnetic transient program PSCAD/EMTDC. With parallel resistors, the switching overvoltages are less than 1.70 p.u. （1.0 p.u.=1100×√ 2 /√3 kV）. If the arrestors are better, the switching overvoltages can be reduced even lower to 1.55 p.u. Without parallel resistors, the arresters can reduce three-phase energizing overvoltages to 1.70 p.u, while the single-phase reclosing overvoltages still exceed the limit. The results show that the parallel resistors cannot be eliminated if the arresters are only installed at each end of the transmission line. Also, better quality arresters significantly lower the switching overvoltages.

UHV交流输电线路对调幅广播收音台防护间距

为研究特高压交流输电线路对调幅广播收音台的防护间距,通过特高压交流试验基地的实测数据,得到了特高压交流输电线路的无线电干扰水平,为有源干扰的计算提供了强有力的数据支持。利用NEC电磁计算软件,建立了特高压输电线路的实体模型,计算了无源干扰随频率、入射角度以及防护间距的变化规律,得到了特高压交流线路3种典型塔型的无源干扰水平。最后通过比较有源干扰和无源干扰影响,给出了特高压交流架空输电线路对调幅广播收音台的防护间距计算值。

UHVAC输电线路大跨越段的防雷保护

为确保特高压输电线路的耐雷可靠性,对晋东南-南阳-荆门UHV输电线路的黄河大跨越段和汉江大跨越段的雷电性能进行了研究并介绍了UHV输电线路大跨越段雷电性能评估的计算方法,同时根据我国输电线路大跨越段的运行情况,参考俄罗斯标准,以大跨越段在雷电过电压下的雷击无故障时间(耐雷指标)来确定防雷保护方案,还计算了UHV输电线路大跨越段的年绕击跳闸次数和年反击跳闸次数及雷击避雷线跨越档距中央的反击跳闸次数,提出了按雷电过电压要求的跨越塔塔头间隙。研究表明,我国特高压输电线路大跨越段的耐雷指标不宜<50 a。

对AC UHV输电线附近可听噪声预测公式的评估

特高压输电中,导线的选择是由输电线下的可听噪声大小决定的,所以可听噪声的预测十分重要。为了从不同机构总结出的多种半经验公式中选择最适合用来预测我国特高压交流输电线下可听噪声大小的公式,结合我国对特高压交流输电线的要求,将相导线水平和正三角排列方式下可听噪声大小的不同预测结果与测量结果进行对比和分析。结果表明:相导线水平排列大雨时可用ENEL公式或IREQ公式计算,小雨时可用ENEL或GE公式计算;相导线正三角排列大雨时可用ENEL公式或BPA公式计算,小雨时只有BPA公式最适合。所以,我国特高压交流输电线下可听噪声的计算在相导线水平排列时选用ENEL公式,相导线正三角方式排列时选用BPA公式。

UHV输电线路对中波导航台无线电信号的干扰

为分析1000kV特高压输电线路对中波航空导航台的无线电干扰情况,在国家电网特高压交流试验基地进行了飞行试验。利用机载全球卫星定位导航系统(global positioning system,GPS)和地面GPS连续采集直升机穿越特高压线路的飞行数据,采用精密单点定位技术确定飞机航迹,并与理论航迹进行比较。试验结果表明:1000kV特高压线路对中波航空导航台无线电的干扰与飞机距离特高压线路的远近和飞机飞行高度没有明显关系。

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。

直流UHV线路杆塔规划及经济档距的确定

为降低直流特高压(UHV)输电线路的工程投资,结合±500 kV和国外已建UHV的经验,分析了现有杆塔荷载和经济档距。根据工程实际情况,计算了塔型方案中各塔的摇摆角系数、水平档距、垂直档距、摇摆角角度及塔头间隙等。计算确定,在理想平地情况下的经济塔高为51 m、经济档距为510 m。研究结果已被应用于云广±800kV线路。

超/特高压直流输电工作环境中纯铜部件点蚀行为

超/特高压输电是实现全球能源互联的核心技术。作为应用最广泛的输电系统导体材料,铜及铜合金的耐蚀性被重点关注。在超/特高压直流输电过程中,周围环境存在较大磁场,导致铜部件的服役环境与普通输电环境不同。采用动电位极化、电化学阻抗谱和元素分析等方法对纯铜在超/特高压环境下的电化学腐蚀行为进行了研究。结果表明:在超/特高压环境下,纯铜在3.5%NaCl溶液(质量分数)中的极限扩散电流高于无磁场条件下的极限扩散电流,并且无磁场条件下的反应电阻比施加了0.1 T磁场条件下的反应电阻明显提高。结合电化学阻抗谱、X射线衍射及元素分析可知,0.1 T磁场会使纯铜的耐蚀性降低,主要腐蚀产物为氧化亚铜。

特高压输电线路磁场对电力金具材料摩擦磨损的影响

目的通过分析特高压直流线路工频磁场环境对电力金具材料磨损行为的影响,探究其磨损机理,为联接金具的磨损失效预测提供理论依据。方法分析线路实际运行参数,计算工频磁场强度,采用自制电磁线圈与M-2000型磨损试验机相结合,通过分组控制变量法研究额定工况下金具材料的磨损过程,以及不同磁场强度下材料的磨损行为。结果在磁场环境中材料的磨损程度远小于无磁场情况下。在0~800 A/m范围内,随着磁场强度的增加,摩擦因数稍降低,质量损失量和磨损率呈下降趋势。在不同磁场强度下磨损试样均呈现越贴近摩擦接触表面区域其显微硬度越高,且随着纵深向后呈递减趋势。在无磁场情况下,磨损接触表面的犁沟较深,遍布锯齿型边缘的凹坑和山脊型微凸峰。在磁场环境中试样的接触表面和磨屑表面更加光滑平整,且氧含量明显升高。结论在无磁场情况下,接触表面为严重的磨粒磨损和黏着磨损。在磁场环境中,磨损试样在短时间内经历了初期磨合阶段和磨损加剧阶段,从而加速过渡到稳定磨损阶段,由严重的磨粒磨损和黏着磨损加速向轻微磨损转变。稳定阶段的主要磨损机制为氧化磨损,并伴随着轻微的磨粒磨损、黏着磨损,以及两摩擦副与磨屑“阻隔层”之间的三体磨损。工频磁场环境对试样磨损起到了一定的减摩作用,磨损程度减轻。