Analysis on the Transfer Characteristics of Rogowski-coil Current Transformer and Its Influence on Protective Relaying

This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency characteristics and transient characteristics of Rogowski transducer and Rogowski-coil Current Transformer are deeply analyzed based on the physical structure of the transformer.?It is revealed that broad bandwidth of the transformer can improve the performance of protective relaying, and the bandwidth is determined mainly by the parameters of the Rogowski transducer and signal processing circuits. It is also discovered that the measurement errors of transient current mainly depend on the abilities for the current transformer to reproduce an accurate replica of the decaying dc components, which is mainly decided by the decay time constant of the aperiodic component of transient current and the parameters of the integral unit. Finally, some measures are proposed for the performance improvement of Rogowski-coil Current Transformer to meet the requirements of protective relaying system in terms of structural design and testing standards.

Parametric effect of large impulse current excited coil on electromagnetic force in coil-sheet system

Based on the method of controlling welding stress with trailing, the electromagnetic force in coil-sheet system was simulated with finite element software ANSYS. The effect of parameters of coil on the electromagnetic force density fy was analyzed. The results show that the maximum electromagnetic force density fy, max in sheet appears in the position near the inner radius of single-turn coil. The position is independent of section shape of coil. fy, max for flat coil is larger than that for long coil and the coil with wedge shape section, while section areas of all coils are equal to each other. The effect of turn number of multiple-turn coil on fy is dependent on the loop resistance in circuit. The kind of coil with more turns and larger inductance is commended while there is larger loop resistance in circuit. fy increases in a certain magnitude while a magnetic core is located in coil. However, the magnitude of fy is limited by saturating magnetic flux of the core.

Design of a Rogowski Coil with a Magnetic Core Used for Measurements of Nanosecond Current Pulses

A Rogowski coil is developed to detect the nanosecond pulse signals of the discharge current with a wide bandwidth of 800 kHz to 106 MHz and high sensitivity of 2.22 V/A. Performance tests show that the Rogowski coil has both excellent dynamic and static characteristics. Calibrating results and the comparison between the standard current shunt and the developed Rogowski coil for the measurement of nanosecond discharge pulses demonstrate that the developed Rogowski coil can reproduce the actual waveform of the discharge current accurately.

Analytic calculation of magnetic force between two current-carrying coils

Current-carrying coils are basic elements in electromagnetic equipments, for example, in high field magnets from high temperature superconducting wires or tapes. In the assembly of these systems and their current-carrying operation, unavoidable mis- alignment and shift from the original position can be induced by disturbances such as the imbalance of magnetic force due to safety problems. For two current-carrying coils with non-coplanar axes, the analytic expression of the magnetic force between the two coils is presented according to the rule of Ampere circulation and the Biot-Savart law. Based on the expression, the dependence of the magnetic force on the size and the relative position of each other is further investigated, and the variation of the magnetic force is obtained with the above parameters.

Current-Bounded Commutation of a Long-Stroke Magnetically Levitated Stage with Moving Coils

Magnetically levitated stages（MLS） have potentials to obtain good motion performances in high vacuum environment. Yet the electromagnetic forces/torques corresponding to six degrees of freedom（DOF） motions have coupling relationship with each current of coil array, and this coupling is still associated with the relative positions between the mover and the stator of the stage. So it is quite difficult to control the 6-DOF motions of the stage. By reasonable commutation of coil array, this complicated coupling relationship can be decoupled. The analytical force/torque-decomposing model of the stage is established first. Then the initial currents of coil array are commutated based on the pseudo inverse of the analytical force/torque-decomposing model matrix. And then the coil array currents are commutated again with different current bounds given to the initial currents as well as in the sense of minimum 2-norm of currents vector. Using the long stroke magnetically levitated stage with moving coils under investigation as examples, the currents of coil array are commutated with different current bounds adopting the proposed commutation method, the determination of current bound and the current bounds＇ influences on the heat-losses in coil array are analyzed, and the effectiveness of implementation algorithm of proposed commutation method is discussed. Simulation, analysis and discussion results indicate that the currents of coil array within the given current bound can be solved analytically by proposed commutation method, and the implementation algorithm does not need any searching or iteration. By the current-bounded commutation method proposed, the amplitude of coil array currents can be limited within an appropriate current bound（This is very beneficial to the improvement of the reliability and motion performance of the stage）, as well as these currents can also generate the desired forces and torques.

Analytical solutions of transient pulsed eddy current problem due to elliptical electromagnetic concentrative coils

The electromagnetic concentrative coils are indispensable in the functional magnetic stimulation and have potential applications in nondestructive testing. In this paper, we propose a figure-8-shaped coil being composed of two arbitrary oblique elliptical coils, which can change the electromagnetic concentrative region and the magnitude of eddy current density by changing the elliptical shape and/or spread angle between two elliptical coils. Pulsed current is usually the excitation source in the functional magnetic stimulation, so in this paper we derive the analytical solutions of transient pulsed eddy current field in the time domain due to the elliptical concentrative coil placed in an arbitrary position over a half-infinite plane conductor by making use of the scale-transformation, the Laplace transform and the Fourier transform are used in our derivation. Calculation results of field distributions produced by the figure-8-shaped elliptical coil show some behaviours as follows： 1） the eddy currents are focused on the conductor under the geometric symmetric centre of figure-8-shaped coil; 2） the greater the scale factor of ellipse is, the higher the eddy current density is and the wider the concentrative area of eddy current along y axis is; 3） the maximum magnitude of eddy current density increases with the increase of spread angle. When spread angle is 180°, there are two additional reverse concentrative areas on both sides of x axis.

MAGNETOELASTIC BENDING AND STABILITY OF CURRENT-CARRYING COIL STRUCTURES

As a results of magnetoelastic interaction, the mechanical behavior of current-carrying coil structures, such as deformation and instability, is a key problem in the design of strong held magnets. In this paper, a nonlinear mathematical model is presented to describe the deformation and buckling of D-type current-carrying coils, based on the Biot-Savart law and the bending theory of curved beams. The bending deformation, the critical value of current for the magnetoelastic buckling of the current-carrying coil, and the effects of the type and number of supports at middle part of the bending coil on the critical value are quantitatively investigated by a semi-analytical and semi-numerical method. The numerical results are shown to be in good agreement with the experimental data.

Experimental Analysis on Shielding Effect of the Grounding Electrodes Under Impulse-current

Generally,the flow of a lightning impulse current from a grounding electrode into ground is a very complicated process determined by many factors.In order to analyze the mechanism of the impulse current dissipating in the earth from grounding electrode,the experiments that had been carried out by other authors almost used a single horizontal grounding wire or vertical grounding rod for sake of simplicity.However,in practical conditions,most of the grounding systems are constructed of grounding electrodes with branches in different directions.In this study,basing on the principle of dimensional similarity,impulse simulation experiments are performed on the common ground electrodes with conductor branches.This paper focuses on analyzing the impulse current dispersal regularity of different branches when injecting at one point.Comparing with the leakage current distribution of a single ground electrode,it is found that the leakage currents along the branches increase with the distance to the current feed point,and the more conductors near the injection point,the more uneven the leakage current distribution is.This work indicates that shielding effect should be taken into account when analyzing the impulse characteristics of grounding electrodes.

Fabrication of HTS dc Bias Coil for 35 kV/90 MVA SFCL

---For a saturated iron core fault current limiter, superconductor is the only suitable material to make the dc bias coil, especially when the device is used in a high voltage power grid. Commonly, superconducting wires are used to wind the dc bias coil Since the performance of the wires changes greatly under magnetic fields, the calculation of the field spatial distraction is essential to the optimization of the superconducting magnet. A superconducting coil with 141000 ampere-turns magnetizing capacity made of 17600 meters of BSCCO 2223 HTS tapes was fabricated. This coil was built for a 35 kV/90 MVA saturated iron-core fault current limiter. Computer simulations on magnetic field distribution were carried out to optimize the structural design, and experiments were done to verify the performance of the coil The configuration and the key parameters of the coil will be reported in this paper.

用于小电流测量的柔性罗氏线圈设计

保障电力系统的安全运行对国家和人民至关重要。因此,须及时监测设备的性能与可靠性。其中,对设备电流的测量是相当必要的。基于罗氏线圈具有出色的线性度并且精度高,选择采用罗氏线圈作为电流传感器。但以往的线圈在测量小电流时,灵敏度低,精度低,适合对大电流的测量。针对以上问题,进行用于小电流测量的柔性线圈设计,相比刚性线圈,其轻便且安装快捷。该线圈使用硅橡胶电缆作为骨架,双层绕线增大线圈互感,有效提高了线圈的灵敏度。通过对工频电流的测量,最终灵敏度约为40mV/A,满足电力系统中的小电流测量要求,可应用于实际工程中。

高压SF_(6)断路器电流零区测量研究综述

电流零区测量对标定评价断路器开断性能、改进断路器结构设计至关重要,设计一套高精度、便携、可靠、安全的零区测量系统一直是行业的追求,国内外研究者在测量方法和测量装置研制方面做了很多创新性工作。从高压断路器灭弧原理出发,梳理提出了零区测量的难点和关键点,综述了国内外研究者提出的测量方案及效果。综合考虑多维度产业需求,研制了一套便携性和动态特性好的零区测量系统,并在实际断路器产品试验中进行了验证。结果表明:该系统抗干扰性和重复性好,能够满足产品研发需求。结合零区测量系统研究及使用经验,提出了零区测量系统的未来展望,为后续交直流开关的研发提供参考。

同轴多层筒式空心线圈自感和互感解析计算方法

在电磁耦合的无线电能传输系统中,准确获取线圈电感参数是设计和优化无线电能传输系统的重要理论依据。现有的无线电能传输系统研究大多针对平面板结构线圈,同轴多层筒式空心线圈相比于平面板线圈具有更高的传输功率和传输效率。因此,该文针对同轴多层筒式空心线圈,提出了一种考虑高频涡流效应的自感和互感解析计算方法。首先,将单匝线圈截面离散等效为数量众多、形状相同的网格带电圆环单元,采用离散等效求和法推导出单匝线圈的自感和线圈间互感的解析式;然后,基于筒式空心线圈的整体结构以及考虑高频涡流效应,推导出基于第一类、第二类完全椭圆积分和开尔文函数的一、二次线圈自感和总互感计算的理论解析式;最后,以两种不同排布方式的筒式空心线圈为例,对比解析计算、有限元计算和实验测量结果,验证了所提解析法的可行性,同时也为筒式空心线圈的设计提供参考依据。

基于功率恒定的防饱和在线取电方法

基于厄流线圈取电装置提出了一种防止铁磁磁心饱和的方法,该方法使用旁路泄流电路将流入电流互感器过多的电流引入到旁路电路中消耗掉,将输出功率作为反馈值来调节旁路电路中开关管的关断,通过控制输出的功率大小,输电线路在宽范围电流内实现恒功率输出和防止电流互感器磁心到达饱和。根据电流互感器各方面的要求,建立电流互感器3D模型,将3D模型导入到Maxwell中对电流互感器本身进行有限元仿真分析,得到电流互感器内部各项参数,再将经过有限元分析的电流互感器模型导入到ANSYS中与外部电路组成取电电路进行联合仿真,通过仿真结果验证电流互感器的取电能力。再加入本次对电流互感器取电优化部分,通过电流互感器二次侧谐振的方式增加一次侧输电线路的等效阻抗,考虑到电流互感器磁心饱和的问题,采用旁路泄流电路将过多的电流通过旁路绕过电流互感器一次侧回到输电线路当中的方法解决。

Combined Digital Electronic Current and Voltage Transducer

A high performance current and voltage measurement system has been developed in power system. The system is composed of two parts: one current measurement element and one voltage measurement element. A Rogowski coil and a capacitive voltage divider are used respectively for the line current and voltage measurements. Active electronic components are used to modulate signal, and power supply for these components is drawn from power line via an auxiliary current transformer. Measurement signal is transmitted by optical fibers, which is resistant to electromagnetic induction and noise. With careful design and the use of digital signal processing technology, the whole system can meet 0.5% accuracy for metering and provides large dynamic range coupled with good accuracy for protective relaying use.

变阻抗高温超导限流器的限流特性研究

超导限流器在系统短路限流中具有良好的应用前景,但是电阻型超导限流器在深度限流后难以快速恢复,针对此问题本文提出了交流系统中的一种基于组合超导线圈的变阻抗超导限流器,能在增大限流率的同时显著缩短主通流支路超导带材的通流时间。基于单根超导带材的实验结果在Simulink中依次建立了单根超导带材和变阻抗超导限流器的R-Q仿真模型,仿真分析了变阻抗超导限流器的限流性能和恢复性能,并通过实验验证了仿真结果的准确性,最后在10 kV交流电力系统中分析了变阻抗超导限流器的限流效果。结果显示,本方案超导限流器的主通流和主限流线圈带材根数之比为2∶1时,限流阻抗能增大到常规超导限流器的3倍以上,能有效提高电力系统的稳定性。

PCB罗氏线圈电流传感器积分误差的数字补偿策略

准确可靠的开关电流信息是电力电子变换器实现闭环控制、谐波抑制和短路保护的关键要素,有利于进一步提升功率器件的可靠性。PCB罗氏线圈电流传感器因其高带宽、小体积、低成本和低侵扰的特点,具有重要的研究价值和应用前景。然而,传统积分处理电路存在漂移误差与下垂误差,严重限制了PCB罗氏线圈电流传感器的测量精度。首先,本文采用复位型积分电路以避免漂移误差的持续累积,并消除下垂误差带来的影响。同时,针对复位型积分电路存在的漂移误差与偏置误差提出一种数字补偿策略,该方案采用数字信号处理器控制数模转化模块产生模拟补偿信号,并通过高速减法器消除误差,具有补偿精度高、调整方式简单的优点,可以大幅减小积分误差造成的影响;最后,基于双脉冲测试平台分别进行双脉冲、多脉冲和短路保护实验,验证了所提PCB罗氏线圈电流传感器的性能。

双线圈并联ICPT系统的分布式补偿电流均衡方法

针对双线圈并联的高功率感应耦合电能传输(ICPT)系统存在线圈间补偿电流不均衡问题,提出一种分布式补偿电流均衡方法。首先提出了双线圈并联ICPT系统的分布式补偿网络,然后依据等效思想和迭代思想提出补偿电流均衡方法,根据该方法求解得到补偿参数和各线圈补偿电流表达式,再将该方法拓展到n线圈并联结构。在北京超算云计算中心的COMSOL云平台验证了所提出的方法不仅有效均衡了各线圈的补偿电流,而且谐振状态受参数漂移的影响程度并未因补偿网络的复杂程度增加而增加。最后搭建了实验平台,验证了所提方法的有效性。

基于桥式驱动电路的磁阻型电磁发射器仿真与实验

在磁阻型线圈电磁发射器中,驱动线圈的剩余电流会影响抛体的发射效率。将磁阻型线圈电磁发射器驱动电路中的电容器用桥式电容电路替代,通过桥式电容电路能够快速降低发射器中驱动线圈的剩余电流,避免抛体在运动时受到反向的回吸力。该文介绍了桥式驱动电路在磁阻型线圈电磁发射器中的工作原理,通过仿真与实验对比分析磁阻型线圈电磁发射器在传统驱动电路与桥式驱动电路中的发射性能。实验和仿真的结果表明:采用桥式驱动电路后,磁阻型线圈电磁发射器的效率得到了提高,剩余电流的能量回收到电容器降低了系统能量的损耗。仿真和实验结果的规律具有一致性,验证桥式驱动电路在磁阻型线圈电磁发射器的可行性,为解决驱动线圈剩余电流及反向力的抑制提供了参考。

海洋平台结构损伤涡流热成像检测激励线圈设计

海上平台作为海上石油开发的重要设施,处在海水浸泡、冲击等恶劣环境中,很容易出现损伤,影响其安全性。管节点作为高应力集中的部位是海上平台结构中更易产生损伤的地方,因此对管节点进行检测十分重要,为适应海上平台管节点这种特殊结构的损伤检测,利用涡流热成像技术,考虑管节点结构、在管节点表面感应出的涡流分布情况等因素,设计出了圆台形线圈、三角形线圈、扁平双线圈三种形式的线圈,并通过COMSOL、SolidWorks完成了相应的仿真模拟,为了符合实验室需求,又构建出了等比例待测工件及线圈的实际模型,通过实验模拟、MATLAB数据处理验证了仿真模拟的准确性及所设计线圈的有效性。结果表明,扁平双线圈对海上平台管节点的加热效果更佳,能够用于对其损伤缺陷的检测。

基于分流器法和罗氏线圈法的静电放电电流测量一致性研究

本文旨在研究不同测量接入方式对静电放电电流测量的一致性,在分析静电放电电流的测量方法的基础上,着重阐述了分流器法和罗氏线圈法的测量原理,对其静电放电电流的测量进行了比对分析。试验表明:两种方法的静电放电电流测量一致性较好,对提高静电放电的防护性能,研究静电放电电流的精确测量具有重要的实际意义。