分析直流母线接地的危害及成因

在内外部运行环境的影响下,变电站直流母线接地故障频频发生,给直流系统可靠稳定运行造成了严重的威胁,同时对电网的运行也造成了十分恶劣的影响。基于此,本文对变电站直流母线接地的成因及其危害展开了一系列详细的分析。     

变电站三维立体接地网设计

为保证系统短路电流快速散失,保证人身和电气设备的安全运行,变电站接地网有着重要的作用。随着电网容量的急剧增加,系统短路故障电流越来越大,同时变电站布置日益紧凑、占地面积较小,按照常规接地网设计,接地电阻值将难于满足规程要求。本文结合渭南110千伏开发区变电站接地网实例,介绍了三维立体接地网设计的基本原理,能够保证接地系统的可靠、长效。     

Electromagnetic Field Emission From Gas-to-Air Bushing in a GIS During Switching Operations

Very fast transient overvoltages (VFTO) and the associated very fast transient currents (VFTC) generated during switching operations in a gas-insulated substation (GIS) radiate electromagnetic (EM) fields, which in turn can leak into the external environment through apertures like SF₆ gas-to-air bushing. Therefore, it becomes necessary to characterize and quantify the EM fields when sensitive control devices are used for the operation of such substations. Keeping this in view, a numerical model using a finite-difference time-domain (FDTD) technique was developed to compute the transient field emission from a 245-kV-rated gas- to-air bushing. Shielding effectiveness (SE) of the bushing for these transient fields was evaluated using a derivative Gaussian current excitation of the high-tension (HT) conductor. The variation in EM field levels along the axis of bushing at various radial distances for different frequencies of the transient current were analyzed. The enhancement of the field levels due to the presence of a metallic structure on the ground plane, which simulates the control cubicle or the grounded enclosures of the GIS, were studied. Finally, the emission levels from different bushing models were calculated for the VFTC generated during a switching event, and the dominant frequencies were identified.     

变电所携带型高压接地线改造设计分析

随着电力事业快速发展,变电站及电网数量、规模都在不断增大,运维人员日常倒闸工作任务量也在增加.对接地线科学装拆,不仅可提高变电所携带型高压接地线的改造设计效率,还可保证操作人员安全,减少安全隐患.本文针对变电所携带型高压接地线改造设计内容进行分析,以期提高供电可靠性和操作安全性.     

Modeling of Transformer Windings Under Very Fast Transient Overvoltages

To calculate the overvoltages in transformer windings under very fast transient overvoltages (VFTOs) generated by switching operations in gas-insulated substation (GIS), a single-input and multiple-output circuit model, which is based on a multiconductor transmission line (MTL) model, is presented in this paper. The procedure to determine the transfer function is deduced. Vector fitting and recursive convolution are used to calculate the time domain response. The resonant frequencies and the location of the resonance are determined by an analysis of the amplitude-frequency response characteristics. For validation, the calculated results are compared with the measurements on a transformer winding model, and the results are found to be satisfactory     

机动雷达地网接地电阻的预估算法

系统接地问题是制约机动雷达机动性能的关键因素之一。通过对垂直地网、水平地网、复合地网三种机动地网技术的理论研究与测试验证,提出了不同地网技术接地电阻的近似计算方法,并在理论推导的基础上,提出了机动地网接地电阻的预估算法。经实际测试证明本文所提算法简单可行,并且已经在某型号机动雷达上开展了实际应用,能够为后续机动雷达应急接地提供重要的技术保障。     

对于变电站直流接地故障的一些看法

变电站作为电力系统运行的重要枢纽,直接关系着电网的正常运行.而直流系统作为变电站继电保护、事故照明、信号、控制系统的电源供给系统,直流接地故障对于变电站运行也有着密切的关联.本文首先对变电站直流接地故障所可能引发的后果进行了简要概述,并对直流系统接地故障的查找与处理进行深入探析,希望能够为相关工作的开展提供一定的参考.     

配网自动化系统小电流接地故障定位方法

在配网自动化系统中,小电流接地故障较为常见,会给电网的运行带来不良影响.基于这种情况,本文对小电流接地故障的定位方法展开了研究,以期通过实现故障快速定位及时排除配网自动化系统故障,继而使电网运行过程中的风险得到有效降低.     

关于变电站直流接地故障的查找及处理方法

本文在介绍直流接地产生的原因及危害基础上,利用直流接地检测仪与万用表分段电压测量法,结合某变电站一起直流接地典型缺陷的处理案例,重点分析变电站直流接地故障的查找步骤和处理方法.实践表明,该方法能够有效解决站内直流系统间歇性出现的直流接地现象,提高系统运行的可靠性.     

浅析消弧线圈在10kV配电网中的应用

随着经济水平的提高,配电网中电缆的使用量日趋提高,由此而产生的电网中容性电流随之增大。传统的接地方式中,中性点不接地运行已经不能保证配电网供电的稳定性。而在中性点经过消弧线圈接地方式运行时,可以很好地补偿电网中发生短路接地时的容性电流。该文通过分析中性点经消弧线圈接地的基本原理及中性点经消弧线圈并电阻、串电阻接地的优缺点,提出一种中性点经可控消弧线圈并电阻接地运行的方式并论证此方式的可行性。     

接地网故障诊断中的拓扑分解算法

为了对接地网进行故障诊断,通过对接地网支路拓扑结构进行分析,提出了一种以可及节点为裂点的分层拓扑分解方法,将接地网分解为元版块网、可及接地网和本征接地网.实现了接地网网络拓扑自动分解,明确了由拓扑结构决定的各层支路的关联性,为采用可测性进行接地网故障诊断奠定基础.对一个60支路的实验接地网采用所提出的算法进行分解,结果验证了提出的方法的正确性和实用性.     

Equations for some transient overvoltage test waveforms

Simple equations are provided that satisfy the definitions of five of the most common transient overvoltage test waveforms: the ringwave specified in ANSI C62.41-1980, the fast transient specified in IEC 801, and the 8/20-μs 1.2/50-μs, and 10/1000-μs waveforms. These equations are useful for performing computer simulations of the response of electronic circuits to transient overvoltages     

Analysis Results of Output Power Loss Due to the Grid Voltage Rise in Grid-Connected Photovoltaic Power Generation Systems

This paper describes the connected photovoltaic (PV) power generation system's grid overvoltage protection function and summarizes the occurrence of the output power loss due to the grid voltage rise. Power injection from the PV system will raise the voltage at the power distribution line. A power conditioning subsystem (PCS) needs to regulate its output if the voltage becomes higher than the upper limit in order to avoid the overvoltage at the power grid. Thus, a PV system cannot generate electricity under the high grid voltage. There are 553 residential PV systems installed in Ota, Japan, for the demonstration research project of clustered PV systems. Measurement data of these 2.1-MW grid-connected PV systems are used for the analysis. Only the limited number of PV systems experienced a significant amount of output energy loss due to the high grid voltage in a particular day, whereas the other system's outputs also raise the grid voltage. The causes of this maldistribution of the output energy loss are the difference of the line impedance, the difference of the starting voltage of the PCS's grid overvoltage protection function, and the imbalance of the load in single-phase three-wire power distribution systems. The present control of the PCS successfully avoids the overvoltage on the grid but cannot share the loss.     

接地网故障诊断的线性最小二乘优化模型及算法

变电站接地网对变电站的安全运行具有重要的意义,是电力运行部门十分关注的问题,近年来也成为学术界研究的一个热点。运用电路基本理论,提出了基于灵敏度分析的线性最小二乘优化模型及算法。首先建立了可测节点电压变化量与接地网导体电阻变化量之间的灵敏度关系线性模型,给出了灵敏度的求解步骤,最后提出了基于线性最小二乘优化模型及算法。通过对一个实际接地网的故障仿真说明,提出的诊断模型和算法具有较高的诊断精度。     

研究变电设备在线监测技术在智能变电站中的运用

智能变电设备是智能电网的重要组成部分,与传统电网相比,智能化是其一大优势,其智能化水平对电网的运行效率有重要的影响,智能化水平越高,其在数据采集和分析时就越快、越准确,这些都可以由设备监测技术实现,因此,在线监测技术在智能变电站中的作用非常重要.本文对变电设备在线监测技术在智能变电站中的应用进行系统阐述和研究,为变电设备在线监测技术在智能变电站中的应用提供参考.     

智能变电站二次系统接地网优化研究

常规变电站对保护小室提出了敷设专用100mm2专用接地铜排环网的要求,但随着智能变电站技术日益成熟,保护下放至继电器小室与保护仓使用增多,使得二次等电位接地网的优化设计成为可能.     

真空断路器投切电抗器过电压分析

对于变压器低压侧负荷较小的运行状况,使用真空断路器投切电抗器可能由于过电压造成设备损坏.本文分析了在投切电抗器过程中产生过电压的原因,提出了过电压抑制方案,并进行了试验验证,试验证明过电压抑制方案切实可行.     

An improved transmission-line model of grounding system

This paper presents a time-domain transmission line model of grounding system, which includes the mutual electromagnetic coupling between the parts of the grounding structure and the influence of air-earth interface. The model can be used to simulate the transient behavior of the grounding system under lightning strike. The simulation results are in good agreement with that of the model based on the solution of full Maxwell's equations. The influence of different parameters, such as the soil relative permittivity ε_τ, the soil resistivity ρ, and the conductivity and diameter of the conductor, on the transient voltage distribution of the grounding system is investigated. It shows that, among the parameters investigated here, the soil resistivity is the most important parameter that affects the transient response of bare buried conductors. The soil permittivity has very little influence on the transient response of the grounding system when the grounding system is buried in the soil with low resistivity, but have moderate influence in the soil with extremely high resistivity. The conductivity of the conductor and skin effect have practically no influence on the peak transient voltage of the grounding system. Increase in conductor diameter tends to decrease the peak transient voltage. The model presented in this paper is simple, but sufficiently accurate and can be used easily in engineering practice. Since the model is in the time domain, it could be easily coupled to the other time-domain models of nonlinear surge-protection components     

Impact of Switching-Induced Electromagnetic Interference on Low-Voltage Cables in Substations

The electromagnetic environment within a substation is very complex. Substations represent an intricate interconnected collection of devices that serve as electromagnetic wave emitters and receptors. Transient electromagnetic emissions—electromagnetic interference (EMI)—are generated during the switching of disconnector and circuit breakers (CBs) that may cause malfunction or damage to electronic equipment positioned nearby if appropriate immunity measures are not taken. The interference may couple significant energy through common-mode currents to cable protection. Electromagnetic compatibility is mostly achieved by addressing the EMI victim through techniques in the secondary environment, such as shielding and filtering. This paper presents the finite-element method analysis of three methods: metallic channel, braided cable, and additional cable, used for EMI mitigation on low-voltage cables of 20 kV side in a 63-kV/20-kV substation due to switching effects of disconnector and CBs. In each method, overvoltage is considered and the results are compared with each other. A simple circuit analysis was also carried out on the causes of switching based on EMI to provide some insight into the interference mechanism during switching process, using common-mode and differential-mode equivalent circuits. The overvoltage reductions are attained through differential-mode current and shielding methods.      

变电站接地网状态检测用虚拟扫频信号发生器

研究一种基于LabVIEW的变电站接地网状态检测的扫频信号发生器,该扫频信号发生器能产生频率随时间作均匀变化且等幅的正弦信号作为被测网络的测试信号。当等幅扫频信号加于被测网络时,网络的输出幅度将按自身的幅频特性变化。通过系统实时、快捷地测试变电站接地网的参数,根据频率特性实现变电站接地网的状态检测,本文所提出的基于虚拟仪器的腐蚀检测方法具有独创性,目前未见有文献介绍,与虚拟仪器结合的变电站接地网状态检测技术具有很好的应用前景。