Development of optical ZCT and its application to fault section detection for 66-kV underground branch transmission lines

The optical ZCT (Zero-phase Current Transformer) which combines an optical magnetic field sensor with a magnetic ring core of silicon steel plates has been developed. Bi-doped YIG [Yttrium Iron Garnet, (BiYbGd)₃Fe₅o₁₂] having a large Verdet constant is used as a Faraday element. The optical ZCT detects the conductor current of 0 to 2000 A at high resolution and has been applied to the fault section detection system for 66-kV underground branch transmission lines which monitors a multiterminal line having Y-branch joint box in on-line state. Optical ZCTs and a section detector/indicator are connected with optical fibers which are capable of nonrepeatedly transmitting signals over 6 km, and allow monitoring long-distance underground power transmission lines. A developed system is now operating on the JR Kasai line (Shinkawa pump line) of Tokyo Electric Power Company.     

Fault section detection system for 275-kV XLPE-insulated cableswith optical sensing technique

An on-line fault section detection system, which continuously monitors a 275-kV cross-linked polyethylene-insulated underground transmission line and instantaneously determines the section of fault at a ground fault, was developed. In the case of a ground fault, the system detects the fault current which flows from the power source to the point of ground fault and determines the fault section from the magnitude and phase information of the fault current. Optical magnetic field sensors based on the Faraday effect are used for detection of fault current, and optical fibers are used for signal transmission eliminating effects of electromagnetic induction due to a large ground fault current (5000-50000 A) or switching surges on signal transmission lines. The distance between an optical magnetic field sensor and the fault section detector/indicator can be as long as 10 km without the use of any repeaters     

Development of fault detector for 33-kV ungrounded power line

A fault section detection system is being developed for 33-kV ungrounded power line. The fault section is obtained from the relation of two point zero-phase currents on power line. This fault detector is composed of optical current sensors and the processing unit and solar battery system. The optical current sensor consists of a Faraday cell and a porcelain bushing. Zero phase current on the processing unit is obtained through a three-phase composer with auto gain control and residual current eliminator. This fault detector has the ability of 0.15 A zero-phase current detection fault factory test; in field tests, this fault detector detects ground fault.     

Development of Fault Section Detecting System for Gas Insulated Transmission Lines

A fault section detecting system using optical magnetic field sensors developed for gas insulated transmission lines (GIL) is reported. A bismuth silicon oxide (Bi12SiO20, or BSO) single crystal was adopted for the optical nagnetic field sensor. A method of mounting the sensors to GIL which enables the sensors to detect the conductor current from outside the enclosure was developed. With the developed fault detector, faults occurring inside a section of GIL between sensors are detected by discriminating the phases of conductor currents detected by the sensors. The system was confirmed to have sufficient performance for application to commercial GILS.     

Application of magneto-optical sensors for fault location in an air-insulated substation bus

A new fault location system using optical current transducers (CTs) to detect faulted sections in the bus bars of directly grounded 275-kV substations has been developed. This system detects fault current by combining optical CTs with wound-type CTs. The new type of optical CT applies a bulk-type Faraday sensor to the combination of windings around a magnetic iron core and a solenoid coil. The optical CT was capable of current measuring over 50 kA. A current differential discriminator combining an optical CT and a wound-type CT verified the operational performance with 40-kA currents. The intended level of fault detection performance was obtained. Based on these results, a system is being made for actual application in 275-kV substations. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(2): 10–17, 1997     

Preventive maintenance system with a different gas injectingfacility for GIS

A preventive maintenance system for gas insulated switchgear (GIS) is developed. It detects signs of trouble and prevents breakdowns in service. The system constantly monitors UHF signals, which are generated by partial discharges (PDs), and propagate in the GIS, by using couplers built into the apparatus. The PDs are detected at high sensitivity (5 pC) and located according to the attenuation of the signals. Then the system injects a different gas into the section where PDs are occurring and improves the dielectric strength. This prevents faults in service and allows remedial actions to be taken with less accuracy. By injecting a small quantity (5-10%) of c-C₄F₈ into the GIS, dielectric strength is raised more than 20%. A preventive maintenance system with a facility to inject a different gas is constructed for a full-scale GIS model. The system detects and locates PDs, and automatically injects the different gas to improve the dielectric strength     

海底高压动力电缆在线监测技术与实验研究

海底动力电缆经常出现故障,为探索寻找电缆监测技术方法,分析了胜利油田埕岛海域海底动力电缆多次出现短路故障的可能原因和产生故障的机理,并由此提出了采用基于BOTDR技术的分布式光纤传感系统监测电缆所受外力变化和监测电缆内部温度变化的技术,以及应用局部放电检测技术监测电缆绝缘破损后放电现象。电缆截面温度场和电缆外表受力的数值模拟分布式光纤传感监测电缆内部不同温度和外部受力变形的实验,以及电缆绝缘破损后的局部放电监测证明,所研究的方法可较好地在线监测动力电缆的工作状态,能有效监测和预测海底高压动力电缆运行中的主要故障,该研究可对海洋动力电缆的健康运行与维护提供一种技术方法。     

Development of Fiber-Optic Voltage Sensors and Magnetic-Field Sensors

The principle, temperature characteristics, and frequency characteristics of fiber-optic voltage sensors and magnetic field sensors are reported, along with the results of an aging test on these sensors. The fiber-optic voltage sensor utilizes the "Pockels" effect of Bi12SiO20 single crystal and the fiber-optic magnetic-field sensor utilizes the "Faraday" effect of ZnSe polycrystal and Bi12SiO20 single crystal. The basic performance of these sensors has been investigated from the perspective of their use as parts in electrical apparatuses. In addition, in this paper some practical applications in electrical substations and transmission lines are presented. These include a fault section detecting system for gas insulated transmission line (GIL), an optical voltage transformer and optical current transformer which are embedded in gas insulated switchgear (GIS), and a surge voltage receiving system.     

Compensation for light intensity variation by superposing AC magnetic field in optical measurement of DC current

Optical voltage and current measurement generally necessitates the compensation of light intensity variation which occurs in the optical measuring system, because it is possible the light intensity variation may give rise to a measuring error. Therefore, such compensation methods as dividing the ac component by the dc component of the light intensity are usefully introduced in optical ac voltage and current measurement, but those methods are not useful exactly for the optical measurement of the quantities including dc components. This paper deals with a new useful compensation method for light intensity variation in the optical dc current measurement. Linearly polarized light passes through two kinds of Faraday sensors, in which one detects dc magnetic field caused by dc current and the other detects externally applied constant ac magnetic field. Then, the compensation of the light intensity variation is carried out by measuring the dc and ac components of the beam. The principle of the compensation method using the ac component is described in the paper. Experimental results of this method using flint glass as the Faraday effect cells are reported and it is clarified that this method can decrease the measuring error of the modulation depth for dc current and compensate light intensity variation validity.     

Fiber-Optics-Based Fault Detection in Power Systems

A fiber-optics-based sensing network applicable for fault detection in power system is presented. The proposed scheme is secure and immune from interferences. At each monitoring location, passive rugged fiber-Bragg-grating-based sensors are deployed. They use fast and compact magnetostrictive transducers instead of current or potential transformers to translate current-induced magnetic field into optical signal. These sensors can be compensated for temperature drift and easily be integrated into an optical sensing network. A broadband light source at a substation scans the change in reflected optical power at a unique frequency band that corresponds to the surge in magnetic field associated with an increased fault current at a certain location. A unique feature of this real-time scheme is that it only requires current information for fault detections in both radial and networked systems with various pole structures and line configurations. It can easily coordinate with other protective devices and is free from any time-current coordination curves. The proposed scheme has been extensively tested by simulations. They confirm that the proposed scheme is able to detect the faults irrespective of the type and location. It also performs well in presence of harmonics, high impedance, and sensors malfunctions, as well as sensor noise.     

采用动态技术测试静态场的光纤测磁传感仪

在根据Mach－Zehnder干涉仅原理制作的各种光纤测磁传感仪中，由于传感臂一般都由磁致伸缩材料与光纤粘合在一起而构成，所以磁性材料所特有的磁致现象将导致重复测量的结果出现不确定的模糊。为了消除这种磁致误差，本文所设计的系统采用磁场扫描技术，除了在传感臂上施加一个频率为ω0的载波场以提高其灵敏度之外，同时还施加了一个频率为ω0的慢速扫描场以使各次重复测量保持相对的动态平衡，这样当被测场与交变的们置场共同作用于传感头时，利用相位检测装置即可得出被测场的大小。本系统可探测的最小静态场为10E－7（Oe／m）。     

基于磁场检测与多判据融合的架空线路接地故障定位方法

针对当前配电网故障区段定位难的问题,提出了一种基于故障点前后磁场差异的故障定位新方法。首先,分析了杆塔处x轴与y轴磁场的分布及其与相电流的关系,同时考虑了三相导线排列差异与数据窗长短对磁场的影响。其次,通过故障点上下游x轴与y轴的磁场差异作为定位依据,分别从不同角度对双轴磁场进行相似度分析,由此构建5种定位新判据。最后,将5种定位判据通过D-S证据理论进行融合,将概率最大的区段判定为故障区段。所提方法综合了各判据的优势,克服了单一判据的适应性问题。通过对高阻故障、噪声干扰等多种工况进行仿真测试,验证了所提方法的有效性。     

Adaptive non-communication protection for power lines BO scheme.II. The instant operation approach

This paper presents an instant operation scheme of a adaptive noncommunication protection technique for power lines. In the technique, protection relays make tripping or reclosure decisions adapting to system and fault conditions without the need for communication links. The noncommunication is achieved by the detection of whether or not the system is in a balanced operation, in order to identify the breaker operation at the remote end of the protected section. In the scheme, the distance relay will trip instantly when a fault is detected outside its zone 1, but within its zone 2 reach. Subsequently, it detects whether the fault is on the protected section or not, and recloses when a fault is cleared from the protected line section. Simulation studies with responses to various system and fault condition have shown that the technique is able to give fast and correct response without the need for a communication link     

SF6电气设备的SO2在线监测装置研究

在线监测SO₂的含量及其趋势变化,对SF₆电气设备的故障预警和故障分析具有极其重要的意义。基于紫外荧光法的SO₂在线监测装置,设计了SO₂紫外荧光检测光路系统、检测电路及软件、在线无损气体采样系统。其中,在线无损气体采样系统不仅能自动采样,还能回收气体,避免待测气体的损耗、泄漏和污染,并支持多种分解气体的同时在线检测。实验测试及现场运行结果表明,该装置完全满足电力设备中SO₂的在线监测需求。     

柔性直流换流站短路工况下直流场磁场计算建模及预测分析

对于安装有混合式直流断路器的柔性直流换流站,直流断路器分断故障电流速度快、内部换流时间短,由故障电流引发的磁场对直流场内二次设备的电磁影响尚不清楚。建立了混合式直流断路器分时段多路径的磁场计算模型,以及平波电抗器、直流母线的磁场计算模型,预测了直流侧发生双极短路故障时定海换流站和张北换流站直流场内二次设备处的磁场,获得了直流场磁场分布规律。计算结果表明：定海换流站和张北换流站直流场现有的二次设备处磁场强度峰值可能达到883 A/m和362 A/m;磁场强度峰值出现在故障电流达到峰值或直流断路器第二次换流阶段;直流场平波电抗器附近和母线布置较多的地方磁场较大。计算结果可为二次设备抗扰度考核和电气设备布置提供参考。     

Decentralised fault detection,identification, and mitigation in excitation control systems

A new intelligent, decentralised, fault detection, location identification and mitigation approach for the excitation control systems of multi-generator power grids is presented in this paper. The proposed approach detects and locates faults in basic components of the excitation systems with a high accuracy and in almost real-time using interval type 2 fuzzy set theory. Once a fault is detected and the location of the fault is identified, a mitigation action follows, where the signal out of the faulty component is automatically replaced by a stabilising signal generated by the fault mitigation system. The mitigation action ensures that the field excitation voltage (thus the terminal voltage of the affected generator) is controlled such that the affected generator and the whole system maintain their pre-fault operating condition. The high accuracy and fast response time aspects of the proposed approach are verified through case studies performed on the IEEE 30 bus test system.     

基于暂态信息的小电流接地故障区段定位

提出一种适用于配电系统架空线路的小电流接地故障区段定位新方法。该方法利用故障暂态电压、电流特征频段内分量计算无功功率,根据故障点前后暂态无功功率方向的不同确定故障区段。在故障信息不易获取的检测节点处,提出利用电磁场感应获取故障暂态信息的方法,通过测量架空线路下方垂直地面方向电场获取小电流接地故障暂态电压信息,测量水平方向磁场获取故障暂态电流信息,详细阐述了最佳检测点的计算思路,并以一典型10kV架空线路为例验证了该方法的可行性。最后阐述了利用该方法实现故障区段定位需要解决的若干关键问题。     

直流SMC铁心高温超导故障限流器的研究

分析了直流电力系统保护的发展现状,设计了一种铁心型高温超导故障限流器。为了尽量延长限流的时间,限流器的铁心采用软磁复合材料(SMC)。限流器在系统正常工作时对电力系统影响很小,当短路故障发生时,它会很快表现为大阻抗以限制短路电流。基于磁场有限元与电路耦合的计算方法,首先对限流线圈在短路过程中的非线性电感进行精确计算,然后结合计算结果,在电路仿真程序中计算短路电流。通过对比SMC与硅钢铁心材料限流器的限流情况,可以看出SMC铁心限流器对于直流电力系统短路故障的限流效果更好。在短路故障发生后8 ms时,该限流器能将短路电流限制到最大值的12%。     

考虑漏磁效应的永磁饱和型故障限流器磁路建模与实验研究

漏磁效应对永磁饱和型故障限流器(permanent-magnet-biased saturation based fault current limiter,PMFCL)的动态特性具有重要影响。针对一种直线式PMFCL的磁拓扑,以铁心磁通的工作零点作为分界阐明了其2个阶段的限流机理,指出铁心磁通自过零反向后将发生畸变,永磁体不再参与限流过程。基于磁场分割原理实现2类等效磁路模型中总漏磁导和漏磁系数的计算,针对拟圆环截面磁通管的漏磁导,提出基于曲线拟合而改变积分变量的求解方法。在Matlab/Simulink环境下建立了考虑漏磁效应的PMFCL仿真模型,分别与小电流和大电流工况的实验结果进行对比,验证了建模方法的有效性。     

Development of a high-speed switching system for distributionnetworks

This paper describes a high-speed switching system for distribution networks which has been developed with the aim of improving power supply reliability (reducing the number of supply interruptions) of distribution systems. When a fault occurs in conventional distribution systems, the fault section is isolated using a sequential time-out control scheme which requires the reclosing and re-reclosing of the entire system. A major drawback of such systems is that normal sections are also subjected to unnecessary power supply interruptions. In order to resolve this problem, the authors have developed a high-speed switching system which isolates only the fault section without interrupting the power supply to normal sections. This new system can fully restore power to the normal sections and completely isolate the fault section within 500 ms in the case of a ground fault