基于故障分量的有功功率极性比较式纵联保护

根据故障附加网络中有功功率的极性特征,提出了基于故障分量的有功功率极性比较式纵联保护原理。其主要思想是:发生内部故障时,附加网络中线路两端有功功率的极性相同;外部故障时两端有功功率的极性相反;正、反向出口处故障时不存在死区问题。借助PSCAD/EMTDC电磁暂态仿真软件,搭建500 k V输电线路模型,对所提方案的动作性能进行了仿真和验证。在此基础上,进一步对比分析了分相保护方案和三相保护方案,并提出了基于故障分量有功功率幅值特征的选相方法。理论分析和仿真结果表明,所提方案能够正确判别区内、外不同类型的故障,抗过渡电阻能力较强,出口故障无死区,两端数据无需严格同步,且不受无功因素影响。     

输电线路虚拟有功功率差动保护

有功功率差动保护在消除线路分布电容影响、应对高阻故障等方面独具优势,但近处金属性故障时的性能缺陷限制了其实际应用。为解决此问题,文中依据叠加原理,提出了虚拟有功功率的概念,并对内、外部故障时线路两端虚拟有功功率的特征进行了分析。以此为基础,提出了分相虚拟有功功率差动保护动作判据,并对其动作特性进行了定性分析。借助PSCAD搭建500kV输电线路模型,全面仿真和评估了不同故障位置、故障类型、过渡电阻、无功元件调整、非同步数据等多种因素对保护方案的影响。理论分析及仿真结果表明,该保护方案可准确辨别故障区间且近处金属性故障无死区,耐过渡电阻能力较强,数据交换量少,同步要求低,无需电容补偿措施。     

Ground distance relay Compensation based on fault resistance calculation

The fault resistance introduces an error in the fault distance estimate, and hence may create an unreliable operation of a distance relay. A new compensation method based on fault resistance calculation is presented. The fault resistance calculation is based on monitoring the active power at the relay point. The compensated fault impedance measures accurately the impedance between the relay location and the fault point. The relay has shown satisfactory performances under various fault conditions especially for the ground faults with high fault resistance. This new compensation method avoids the under-reach problem in ground distance relays.     

A novel power swing blocking scheme using adaptive neuro-fuzzy inference system

A power swing may be caused by any sudden change in the configuration or the loading of an electrical network. During a power swing, the impedance locus moves along an impedance circle with possible encroachment into the distance relay zone, which may cause an unnecessary tripping. In order to prevent the distance relay from tripping under such condition, a novel power swing blocking (PSB) scheme is proposed in this paper. The proposed scheme uses an adaptive neuro-fuzzy inference systems (ANFIS) for preventing distance relay from tripping during power swings. The input signals to ANFIS, include the change of positive sequence impedance, positive and negative sequence currents, and power swing center voltage. Extensive tests show that the proposed PSB has two distinct features that are advantageous over existing schemes. The first is that the proposed scheme is able to detect various kinds of power swings thus block distance relays during power swings, even if the power swings are fast or the power swings occur during single pole open conditions. The second distinct feature is that the proposed scheme is able to clear the blocking if faults occur within the relay trip zone during power swings, even if the faults are high resistance faults, or the faults occur at the power swing center, or the faults occur when the power angle is close to 180°.     

Fast orthogonal search approach for distance protection of transmission lines

A distance protection scheme for transmission lines based on analyzing the measured voltage and current signals at the relay location using fast orthogonal search (FOS) is presented in this paper. FOS has the ability to accurately provide fast estimate of the voltage and current fundamental frequency phasors that are required for a digital distance relay. Compared to the conventional FFT, FOS can estimate the fundamental phasors with higher accuracy and less number of samples. The proposed scheme has been tested on a transmission line model to verify the merit of this approach. The tests presented include solid ground faults, phase faults, and high impedance faults at different fault locations and loading conditions. The proposed scheme can classify all fault cases in less than one cycle after the inception of the faults.     

Data-mining model based adaptive protection scheme to enhance distance relay performance during power swing

The paper presents a data-mining model based adaptive protection scheme enhancing distance relay performance during power swing for both compensated and uncompensated power transmission networks. In the power transmission network, the distance relays are sensitive to certain system event such as power swings, which drive the apparent impedance trajectories into the protection zones of the distance relay (zone-3) causing mal-operation of the distance relay, leading to subsequent blackouts. Further, three-phase balanced symmetrical fault detection during power swing is one of the serious concerns for the distance relay operation. This paper proposed a new adaptive protection scheme method based on data-mining models such as DT (decision tree) and RF (random forests) for providing supervisory control to the operation of the conventional distance relays. The proposed scheme is able to distinguish power swings and faults during power swing including fault zone identification for series compensated power transmission network during stress condition like power swing. The proposed scheme has been validated on a 39-bus New England system which is developed on Dig-Silent power factory commercial software (PF4C) platform and the performance indicate that the proposed scheme can reliably enhance the distance relay operation during power swing.     

基于阻抗比较的同杆并架选相新方法

首先对综合比相阻抗继电器在同杆并架双回线故障下的动作行为进行了研究,在此基础上提出一种结合综合比相继电器的选相新方法。这种选相元件根据改进后的综合比相继电器的选相结果,参考测量阻抗值对已选出的动作相再次进行筛选。同杆并架的后备距离保护应用此选相元件,通过适当的整定配合,能可靠地区分靠近线路末端跨线故障和区内相间故障,提高距离保护I段的正确动作率。数字仿真结果表明,基于阻抗比较的同杆并架选相新方法受同杆并架线路拓扑结构和对称性等因素影响小,能保证后备距离保护I段在各种线路运行方式下正确选相跳闸。     

A novel protection scheme for synchronous generator stator windings based on SVM

This paper proposes a novel scheme for detecting and classifying faults in stator windings of a synchronous generator (SG). The proposed scheme employs a new method for fault detection and classification based on Support Vector Machine (SVM). Two SVM classifiers are proposed. SVM1 is used to identify the fault occurrence in the system and SVM2 is used to determine whether the fault, if any, is internal or external. In this method, the detection and classification of faults are not affected by the fault type and location, pre-fault power, fault resistance or fault inception time. The proposed method increases the ability of detecting the ground faults near the neutral terminal of the stator windings for generators with high impedance grounding neutral point. The proposed scheme is compared with ANN-based method and gives faster response and better reliability for fault classification.     

Wavelet based transformer protection using high frequency power directional signals

This paper proposes a novel wavelet transform based relaying scheme for power transformer protection. The relay logic consists of two parts: disturbance detection based on first level high frequency details of the voltage signals only and fault discrimination using a power based directional signal derived from the first level high frequency details of both voltage and current signals. The logic is deterministic, computationally efficient, fast, secure and highly reliable. The operating time is 6 ms, about 1/3rd of power frequency cycle (20 ms). The scheme uses only the sign of the directional signals, rather than the difference in their magnitudes, hence it can work reliably in the presence of transformer tap variation, fault resistance and CT saturation. The validity of the proposed logic was exhaustively tested by simulating various types of internal and external faults, energization conditions and load variations on a 132 kV system modeled in ATP/EMTP with a 31.5 MVA, 132/33 kV, Y–Δ transformer. The proposed logic was able to correctly discriminate between internal faults, external faults and non-fault disturbances for all the 880 test cases.     

A New Weak Fault Component Reactance Distance Relay Based on Voltage Amplitude Comparison

A new weak fault component reactance distance relay is proposed in this paper. By adaptive setting of the compensated voltage, the scheme synthesizes the performance of the impedance distance relay and the reactance distance relay. The distance protection relay on the receiving end will misoperate when the fault resistance is larger than the critical resistance. So a new switching criterion is applied to eliminate this disadvantage. Based on that, the proposed scheme can detect the fault with the high fault resistance in the setting coverage, regardless of whether the relay is located at the receiving end or the sending end. Test results from the simulation and experimental conditions show that the new scheme is successful in detecting the internal fault. It has higher sensitivity and selectivity during different conditions than the traditional fault component protection schemes.     

A novel protection scheme for synchronousgenerator stator windings based on SVM

Integration of electric vehicles (EVs), demand response and renewable energy will bring multiple opportunities for low carbon power system. A promising integration will be EV battery swapping station (BSS) bundled with PV (photovoltaic) power. Optimizing the configuration and operation of BSS is the key problem to maximize benefit of this integration. The main objective of this paper is to solve infrastructure configuration of BSS. The principle challenge of such an objective is to enhance the swapping ability and save corresponding investment and operation cost under uncertainties of PV generation and swapping demand. Consequently this paper mainly concentrates on combining operation optimization with optimal investment strategies for BSS considering multiscenarios PV power generation and swapping demand. A stochastic programming model is developed by using state flow method to express different states of batteries and its objective is to maximize the station’s net profit. The model is formulated as a mixed-integer linear program to guarantee the efficiency and stability of the optimization. Case studies validate the effectiveness of the proposed approach and demonstrate that ignoring the uncertainties of PV generation and swapping demand may lead to an inappropriate batteries, chargers and swapping robots configuration for BSS.     

超导磁储能装置对输电线路多边形特性距离保护的影响分析

超导磁储能(SMES)装置响应速度快,能够对有功、无功进行独立控制,在电力系统中将得到越来越广泛的应用。SMES并入系统后的充放电过程会与电网双向交换功率,可能会对输电线路的继电保护产生影响,造成保护装置的不正确动作。在建立SMES电磁暂态仿真模型的基础上,在PSCAD环境下研究了含SMES的单机无穷大系统(SMIB)输电线路多边形距离保护的动作特性,针对不同短路故障类型和SMES的不同安装位置分析了多边形距离保护的动作结果。仿真结果表明,SMES并入电网后多边形距离保护的测量阻抗发生了变化,在某些情况下会对保护的动作结果产生影响。最后提出了一个保护动作特性曲线的改进方案,并通过仿真试验验证了其可行性。     

A New Pilot Protection Scheme Based on Virtual Sequence Transition Impedance

A new pilot protection scheme for transmission line based on virtual sequence transition impedance is proposed in this paper. When the out-zone fault occurs, the value of the imaginary part of the virtual sequence transition impedance is greater than the relay setting value of fault location. For internal faults, the current calculated is high as the protection startup threshold and the value range of the imaginary part of each virtual sequence transition impedance is much less than the setting value, which distinguish the fault types at the same time. Compared with the traditional methods, the proposed method is not affected by the fault location, fault types, transition resistance, line capacitance current, and weak feed line fault. Furthermore, the setting value does not need to be settled and the setting rule is clear.     

Discriminating transformer large inrush currents from fault currents

One of the most widely used approaches for transformer protection is the low impedance differential relay, which can be adversely affected by inrush currents. Although the conventional inrush current detectors, i.e. the gap detection and second harmonic criteria, can block the differential relay in most of such cases, they are severely prone to maloperation in the case of large inrush currents. This paper presents a new strategy to enhance the security of the differential relay. The suggested approach exploits an intrinsic feature of large inrush currents in three-limb three-phase transformers with the widely used star-delta connection. Based on the feature, some novel criteria are proposed to improve the inrush current detection scheme. To evaluate the performance of the proposed approach for both inrush current and internal fault phenomena, a real 230/63-kV power transformer is modeled based on the time-based transient simulation. Extensive simulation studies and also evaluation using real data reveal that the proposed approach results in a more secure inrush current discrimination method.     

A new adaptive PMU based protection scheme fortransposed/untransposed parallel transmission lines

This paper proposes a brand-new adaptive phasor measurement unit (PMU) based protection scheme for both transposed and untransposed parallel transmission lines. The development of the scheme is based on the distributed line model and the synchronized phasor measurements at both ends of lines. By means of eigenvalue/eigenvector theory to decouple the mutual coupling effects between parallel lines, the fault detection and location indices are derived. The two proposed indices are used in coordination such that the internal and external fault events can be distinguished completely. By on-line estimation of the line parameters under the actual power system conditions, the proposed scheme will respond more accurately to power system faults. Extensive simulation results using EMTP have verified that the accuracy of the fault location achieved is up to 99.9%. The proposed protection system responds well and fast with regard to dependability and security. All the results show that the performance of the proposed detection/location indices is independent of fault types, locations, resistance, source impedance, fault inception angles, and load flows     

A novel adaptive PMU-based transmission-line relay-design and EMTP simulation results

This paper proposes a novel adaptive relaying scheme based on phasor-measurement units (PMUs) for transmission lines. The proposed adaptive relaying scheme can provide an extremely accurate discrimination between in-zone and out-of-zone faults. Two novel and composite fault discrimination indices in terms of Clarke components of synchronized voltage and current phasors at two ends of a line are derived. A line parameter estimation algorithm is developed and built in the newly designed relay to solve the uncertainty problem of line parameters. The proposed relaying scheme is independent of fault types, fault locations, fault path resistance, fault inception angles, and the variations of source impedance. The tripping decision time of the designed relay is very fast and almost held well within 6 ms for most fault events. All of the EMTP simulation results show that the proposed adaptive relaying scheme provides a high level of dependability and security.     

基于数学形态学的电力系统振荡中故障识别和改进的选相方法

为了使振荡闭锁装置能在振荡中再故障时开放保护,就必须能区分振荡与故障,且故障相的单相阻抗继电器在振荡时也应能正确测量阻抗。但如何在振荡中快速正确地选出一个故障相进行阻抗测量是距离保护能否有选择性地切除振荡中故障的关键问题。在动模实验中发现:对于振荡中发生的故障,在一定情况下序分量选相元件会误选相。文中利用级联多分辨形态梯度变换(SMMG)提出了一种电力系统振荡中的故障检测和改进的故障选相方案:先利用一个SMMG滤波器对相电流进行处理,构成一个自适应的振荡中故障起动元件;检测到故障或扰动后,对接地故障,如果由现有的序分量选相方法判断出其为落在包含单相和相间2种故障类型的区域,则可利用故障后3个模电流分量的SMMG系数局部模极大值确定其故障相别。用EMTP在一个系统模型上进行了大量的仿真研究,其结果验证了该方案的有效性和易用性,该方法判别灵敏,结果可靠,所提出的算法易于实现,在现有的微机保护装置中可以直接采用。     

A new PMU based power swing detector to prevent mal-operation of distance relay

In conventional transmission line protection, a distance relay is used to provide the primary as well as remote backup protection. The voltage and current phasors measurement needed by the distance relay for determining the impedance may be affected by the power disturbances such as power swing. Consequently, this power swing may cause mal-operation of Zone three distance relays which in turn may affect on the reliability of the whole protective scheme. To mitigate these effects and hence improve the relay reliability, this work proposes a new real-time power swing detector using phasor measurement units for blinding the distance relay only during this transient disturbance. However, this developed detector will not block relay when the power swing accompanied with faults. To validate the present work, the performance of developed enhanced distance relay is tested by signals generated by Simulink/MATLAB simulator under different conditions. The test results show that this proposed scheme provides good discrimination between the transient currents and the fault current which in turn it may contribute in enhancing the reliability of Distance relay.     

Novel transient-energy-based directionalpilot protection method for HVDC line

In long transmission lines, the charging current caused by the shunt capacitance decreases the accuracy in impedance based fault location. To improve the accuracy of fault location, this paper presents a novel scheme, where two Digital Fault Recorders (DFRs) are installed in a line. They can send the transient data of the faults to the both ends of a line. To estimate the distance of a fault, impedance based fault location methods are applied with transient fault data of both ends protection relays and both DFRs installed in a line. To evaluate the proposed scheme, a laboratory setup has been developed. In the lab, several faults have been simulated and associated voltages and currents are injected to a relay IED to compare experimental results.     

Laboratory investigation of a distance-protection technique for double circuit lines

A novel digital distance scheme has been implemented on a 32-bit digital signal processor board. The scheme is tested on a physical model of double circuit lines of equal impedance with a source at each end. Two relays instead of four are proposed for the two lines. Each relay is fed by three voltage and six current signals. The technique is based on the comparison of the measured impedance of the corresponding phases. Tests conducted on the physical model for various faults show that high fault resistance, current in-feed, balance-point location, out-of-step operation, and far-end faults are solved. Moreover, 100% of the line is protected.