Adaptive distance protection of a double-circuit line

Due to changes in the power system, such as generator and line outages and changes in load and generation, the performance of distance relays can vary. In the case of a distance relay protecting a phase of a double-circuit line, the state of the parallel circuit is of major importance. Simulations show that, depending on the power system state, a distance relay can cover from less than 50% up to far more than 100% of the total line length. This is demonstrated with a double-circuit line under the single-line-to-ground fault (SLG) fault condition, since this is the most common type of fault. In this paper the distance protection of a double-circuit line under the SLG fault condition is formulated. To achieve correct operation, the relay does not only use the measured quantities of the circuit-to-be-protected, but also the zero sequence current of the parallel circuit. Such a relay requires extra measuring equipment, and, moreover, the zero sequence current of the parallel circuit cannot always be measured. Therefore, another approach is chosen. A correction factor is introduced, set adaptively according to the actual power system state. In this way, the appropriate setting of the relay is provided, in relation with the actual power system state. A side-effect of the adaptive setting of the relay is that the safety margin in the relay settings is decreased, due to the uncertainty in the power system state. By adapting the relay to the actual power system state, maximum selectivity is achieved, and the protection system as such will be more reliable     

同杆输电线路零序参数对基于感受阻抗法接地距离保护Ⅰ段的影响

基于感受阻抗的接地距离保护整定计算方法在电力系统中得到了广泛应用。该方法的正确性与实际测量参数的正确性密切相关。实际工程中,由于同杆输电线路的零序参数可能存在误差,使得该方法所得的整定值可能产生误差,严重时将造成保护Ⅰ段误动,威胁系统的安全稳定运行。分析了同杆输电线路零序参数的误差对基于感受阻抗的接地距离保护Ⅰ段的影响,提出了计及零序参数误差在接地距离保护I段中的整定方案。     

基于波形系数的自适应距离保护

为了描述非全波波形畸变程度,提出了波形系数的概念。仿真显示,波形系数与电气量幅值误差有明确的关系。针对目前快速距离保护采用的保护范围反时限特性具有保护范围的开放很保守、不能保证远端故障的快速切除等缺陷,提出了基于波形系数的自适应距离保护方案。故障发生后,实时计算波形系数,并根据波形系数自适应地调整保护的整定值,使保护更好地适应系统的故障状况,而不再采用按时限逐步开放保护范围的做法。     

继电保护振荡闭锁的改进措施

振荡闭锁是保障电力系统安全的重要技术环节,是继电保护的理论难点之一。对现有的振荡闭锁方案进行改进,主要包括:改进启动继电器;实时计算短时开放时间;提出振荡闭锁中的对称开放和不对称开放新判据。通过设计故障检测器和启动加速器来提高突变量启动继电器和零序启动继电器的动作性能;用正序电压余弦分量替代静态稳定电流,实时计算暂态稳定破坏短时开放时间代替固定延时;通过加速软开关提高距离保护I段对称开放速度,利用距离保护延时计算U1cos 1来开放保护;在m|U1cos 1|的2维平面上分析振荡和不对称故障的不同特征,改进现有的不对称开放判据。利用实时数字仿真系统进行仿真验证,仿真结果验证了改进方案的正确性和有效性。     

220~750 kV电网线路后备保护整定配合探讨

随着220~750 kV电网线路主保护的加强,业界关于后备保护整定配合的争议越来越多。为了解决后备保护整定配合问题,介绍了高压电网线路后备保护配合整定在现场的几种常用整定方法,分析了不同整定配合方案考虑的原因。针对接地距离测量阻抗受零序补偿系数的影响,分析了接地距离保护整定中需要特殊考虑的问题。通过对高压电网线路后备保护作用分析以及实际案例验证,推荐了一种高压系统后备保护的整定计算方法。     

Fault impedance estimation algorithm for digital distance relaying

Fault impedance is one of the major parameters that must be estimated accurately in digital distance relaying application. In this paper, a new algorithm is proposed based on symmetrical components theory. The proposed algorithm has computational advantage over previously suggested symmetrical components based algorithms. A procedure for applying shunt fault conditions to the sequence equations to estimate fault impedance of the protected transmission line is discussed. The Alternative Transient Program (ATP) that is available on personal computers was used in evaluating the proposed algorithm. ATP models a power system and simulates many fault conditions on a selected transmission line. Fault data obtained were used in calculating fault impedance using the proposed algorithm. Fault impedance estimates were inserted in relay characteristics to determine suitability of the proposed algorithm for first zone distance protection. Sample results of these studies which show stable fault distance estimates are presented and discussed in the paper     

智能技术在距离保护中的应用

针对传统的距离保护方法存在许多不足,提出了一种将BP网络与径向基函数网络相结合的距离保护模型。分别采用BP网络构建振荡识别子网络,采用RBFN构成的故障检测定位子网络,并采用附加动量项和自适应学习率等措施增加BP算法学习过程的稳定性和收敛速度;为增加网络训练的确定性,文中进行了大量的仿真计算,结果表明,该方法能够对电力系统的各种故障情况进行正确的识别并且比目前常用的神经网络式距离保护有更高的工作效率。文章最后也分析了神经网络技术在距离保护中存在的不确定性,指出了消除不确定性的措施。     

An adaptive approach in distance protection using an artificial neural network

All relay settings are a compromise. Adaptive relaying accepts that relays that protect a power system may need to change their characteristics to suit the prevailing power system conditions. This philosophy has a wide range of applications covering many protective schemes. Here we consider a two-terminal transmission line, confirm that fault resistance and the location of faults can produce erroneous relay function and finally suggest ways to ensure the generation of the correct signal for relay operation. Retaining the microprocessor based framework, we show how artificial neural networks (ANNs) can be used effectively to achieve adaptive relaying for the above-mentioned problem. Adaptive relaying covers a large number of applications and the characteristics of relays vary widely, so the philosophy of adaptive relaying must vary accordingly. A modified multilayered perceptron model employs an additional node in the input layer. This additional input facilitates changes in the relay characteristic. The desired change in the quadrilateral relay characteristic is achieved by making appropriate changes in the thresholds and weights of the hidden layer neurons. A multiparameter adaptive scheme assumes that the additional input of the phase angle is available. Simulation results using ANNs for the different applications of adaptive relaying mentioned above are presented and discussed.     

Artificial neural network approach to distance protection oftransmission lines

A distance relay for the protection of transmission lines is usually designed on the basis of fixed settings. The reach of such relays is therefore affected by the changing network conditions. The implementation of a pattern recognizer for power system diagnosis can provide great advances in the protection field. This paper demonstrates the use of an artificial neural network as a pattern classifier for a distance relay operation. The scheme utilizes the magnitudes of three phase voltage and current phasors as inputs. An improved performance with the use of an artificial neural network approach is experienced once the relay can operate correctly, keeping the reach when faced with different fault conditions as well as network configuration changes     

Low cost microcontroller based fault detector,classifier, zone identifier and locator for transmission lines using wavelet transform and artificial neural network: A hardware co-simulation approach

A low cost, fast and reliable microcontroller based protection scheme using wavelet transform and artificial neural network has been proposed and its effectiveness evaluated in real time. The proposed scheme, based on the hardware co-simulation approach performs all the functions of transmission line protection i.e. fault detection/classification, fault zone/section identification and location estimation. The fault detection/classification and zone identification algorithms use fundamental frequency current component to estimate a fault index. The fault location estimation module uses wavelet transform coefficients in hybridization with a parallel artificial neural network structure. For hardware implementation, a 8-bit ATmega microcontroller is used and interfaced with the simulated power system model using Integrated Development Environment (IDE). The scheme is tested on a power system model of 400 kV, 50 Hz three phase double circuit line with source at both the ends. Laboratory tests have been performed in real time for 20,000 fault cases including evolving faults with varying fault resistance, fault inception angle, fault distance, direction of power flow angle and its magnitude. The tests confirm the suitability and reliability of proposed scheme even with Current Transformer (CT) saturation. The implementation of the proposed approach on a low cost microcontroller with the lesser execution time, makes the prototype ideal for implementation on a digital platform (digital relay), thus leading to financial viability and sustainability of the protection scheme.     

Development of a numerical comparator for protective relaying: PartII

This paper describes the testing of a new power system numerical relaying concept. The new technique is applied to distance relaying to offer improved reliability and security of the relay, and improve the speed of relay operation. To validate the algorithm's performance, the scheme was analyzed under a variety of test conditions and compared with conventional relay concepts. This paper presents the results of the testing and shows that the new relaying scheme operated with a high level of security and dependability for all of the test cases. The tests show improvements that the new scheme can offer in comparison to the conventional schemes     

利用二次函数修正微分方程不平衡量的距离保护算法

暂态超越现象的存在,使得距离保护Ⅰ段的作用受到很大限制,保护范围大大缩小,在高压电网甚至超高压电网中,暂态超越现象尤其严重。文中利用二次函数对微分方程中由于互感器特性不一致引起的不平衡量进行修正,能够防止距离保护的暂态超越现象,使得距离保护的动作速度显著提高,保护动作特性明显改善。通过动模数据和实际现场保护录波数据对算法进行仿真验证,结果表明所提出的算法能够明显改善距离保护Ⅰ段的保护性能,有效防止暂态超越。     

Adaptive load blinder for distance protection

This paper proposes a novel adaptive load blinder for distance protection. A distance relay can provide remote backup protection by zones 2 and 3, but it may mal-operate under heavy loading conditions and cause cascading trips in the network, which could further lead to a widespread blackout. To prevent cascading outages, load blinders or load encroachment elements are generally used to block the distance relay when there is heavy load in the system. However, these elements are not always able to discriminate heavy loading conditions from fault conditions, especially for heavy loads with low power factors or faults with fault resistance. This paper presents a novel load blinder scheme for distance protection by using artificial neural network (ANN). Test results show that the proposed ANN-based load blinder scheme is able to discriminate between different heavy loads with a wide range of power factors and different faults with fault resistance.     

Application of a distance relaying scheme to compensate fault location errors due to fault resistance

This paper proposes a distance relaying scheme based on the current phase jump behavior during fault conditions to improve the apparent impedance estimated by the distance relay. For a nonpilot protection scheme, the measured impedance is affected by error due to the combined effects of fault resistance and prefault load. An experimental relation between the current phase jump introduced with fault inception and the X/R ratio seen by the distance protection is deduced. The phase jump correction factor obtained is an exponential function of the X/R ratio of the line. This factor is applied to the apparent impedance measured by the relay and it allows mitigating the adverse effect of prefault power. The relaying scheme improves significantly the accuracy in estimation of the resistive fault location. The application of this scheme does not require communication links from the remote end of line and is applicable to all types of fault.     

基于人工神经网络模型的继电保护的探讨

对神经网络模型的继电保护的发展历史进行了评述,较详细地分析了神经网络在电力系统的母线保护、电流保护和距离保护的应用。回顾并展望了神经网络在继电保护中的应用。     

基于人工神经网络模型的继电保护探讨

对神经网络模型的继电保护的发展历史进行了评述,较详细地分析了神经网络在电力系统的母线保护、电流保护和距离保护的应用。回顾并展望了神经网络在继电保护中的应用。     

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.     

自适应控制在电力系统继电保护中的应用

继电保护需要适应频繁变化的电力系统运行方式,正确切除发生各种故障的设备,而自适应控制能在参数变化时保持系统的标准特性因此,可形成以自适应方式控制的继电保护－自适应保护。为此,介绍了自适应控制系统的模型,并以距离保护为例,说明运用自适应控制解决继电保护整定值设置和调整等问题的方法,给出自适应距离保护模型。     

固定串补电容对工频故障分量继电保护的影响

固定串补电容对工频故障分量继电保护有一定的影响。按Ｋ（Ｚｚｄ－Ｘｃ）整定保护范围时,故障分量距离元件可用于快速切除近端故障,对于远区故障,拒动、误动均有可能。当串补电容的容抗小于系统电源的正序阻抗（含短路点至电源的正序线路阻抗）时,故障分量方向继电器可用于串补线路。     

短线路两相短路时距离保护误差分析

距离保护在高压及超高压输电线路得到广泛应用,随着国内电网建设的加强,高压输电线路的长度越来越短,特别是城市电网中,短线路不断增多,但是短线路在两相短路时,由于测量电压的误差会放大,可能引起距离保护的超越。推导了短线路两相短路时电压测量误差的计算公式,分析了该误差对距离保护的影响。