Active power based distance protection scheme in the presence of series compensators

Flexible ac transmission system (FACTS) controllers, especially the series-FACTS controllers, affect the operation of distance relays and can lead to the relays under/over-reaching. This paper aims to demonstrate the effects of static synchronous series compensator (SSSC) and series capacitive compensation (SCC), as two important series compensators, on the distance protection using theoretical and computational methods. The results of the investigation are used to develop a feasible and adequate method for eliminating the negative effects of these devices on the distance relays. The developed method measures the voltages at terminals of the SSSC and SCC by phasor measurement units (PMUs) which are then transmitted to the relay location by communication channels. The transmitted signals are used to modify the voltage measured by the relay. Different operation types and conditions of SSSC and SCC, and different faults such as phase-to-phase and phase-to-ground faults are investigated in simulations. Since the modeled distance relay can measure the fault resistance, trip boundaries are used to show the performance of the presented method. Results show that the presented method properly eliminates the negative effects on the distance relays and prevents them from mal-operation under all fault resistance conditions.     

Adaptive algorithm for transmission line protection in the presence of UPFC

The presence of flexible ac transmission system (FACTS) controllers in transmission lines causes mal-operation of distance relays. The series-shunt FACTS devices have larger influence on the performance of the relays compare to the other FACTS controllers. Furthermore, high-resistance fault is another factor that relay become under-reach and cannot correctly identify the fault. In this paper, a method is provided based on synchrophasors to eliminate the effects of unified power-flow controller (UPFC) and fault resistance on the distance relay. In the presented method, the data of voltage and current signals of buses will be sent to system protection center (SPC). In SPC, an algorithm is provided based on active power calculation in buses which is able to eliminate the effects of both mentioned factors. The main advantage of the proposed method, in addition to the simplicity of the algorithm, is the ability to operate in all types of faults and in high-resistance faults. Furthermore, a technique is presented in this paper to calculate UPFC data. A comparison has been performed between this technique and another method where UPFC data is directly transmitted to SPC by communication channel. In modeling of UPFC, detail model is used based on 48-pulses voltage source converters.     

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.     

方向高频保护的动作行为分析：第一部分：复杂系统的复故障计算

方向高频保护高压和超高压输出电线路的主要保护方式,其动作性能对电力系统的安全运行影响甚大。     

微机变压器的相间后备保护

提出对变压器内部故障应以两套差动保护互为后备,距离继电器主要作为低压母线及馈线故障的后备保护,并建议采用负序距离继电器和椭圆形继电器为宜     

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.     

Distance-differential protection of transmission lines connected to wind farms

Distance relays are often used in the protection of the transmission lines connected to the wind farms. The distance relay using the transmission line impedance measurement identifies the type and location of the fault. However any other factors that cause the failure of the measured impedance, makes the relay detect the fault in incorrect location or do not detect the fault at all. One of these factors is the fault resistance which directly increases the measured impedance by the relay. One of the methods to eliminate relay under-reach effect is using of the trip boundaries. Trip boundaries are changing with wind variation and following with output power of the wind farms. Therefore, trip boundaries should continuously change proportional by the wind speed. In this paper, a method is provided based on the combination of distance and differential protection. In this method, using active power calculation in both ends of the transmission line, fault resistance is calculated and its effects are directly deducted from the calculated impedance by the relay. Therefore, variable trip boundaries are not needed anymore. Also in this method, unlike the technique that the trip boundaries are used, the exact location of fault and its distance from the relay also is calculated. Detailed model of a doubly-fed induction generator (DFIG) driven by a wind turbine is used in the modelling. Results of studies show that the presented method eliminates properly the mal-operation of relays under all different fault resistance conditions.     

Digital distance protection of transmission lines in the presence of SSSC

In this paper the impact of Static Synchronous Series Compensator (SSSC) on the impedance calculated by distance relay is investigated. Analytical results are presented and verified by detailed simulations. Six different phase to phase and phase to ground measuring units of the distance relay are simulated to resemble the behavior of the relay. It is shown in this paper that zero sequence of the injected voltage by 48 pulse SSSC converter has the most impact on the apparent impedance seen by the phase to ground fault measuring unit and cause under reaching of distance relay. It can be concluded from the results that SSSC located in the middle of the transmission line cause to divide trip characteristics of distance relay into two separate parts. It is also shown that the over-reaching operation of distance relay might happen in some cases in the presence of SSSC. All the detailed simulations are carried out in MATLAB/Simulink environment.     

Effects of VSC based HVDC system on distance protection of transmission lines

The priority to reactive power contribution from the Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) connection to support the grid during faults as suggested by the modern Network Code (NC) for HVDC affects the distance protection of transmission lines. Moreover, suppressing the negative sequence current during an unbalanced condition also interferes with the proper operation of the distance relays. This is because the current contribution from the converter is limited in magnitude and modified in the waveform in order to protect the power electronic devices during the fault in comparison to the synchronous generator fault current characteristics. This paper discusses the cause as well as the severity of the problems faced by the distance protection of transmission lines connected to the VSC based HVDC system by analyzing the apparent impedance analytically and in the simulation. The response of the relay to balanced and unbalanced faults lying on transmission lines is investigated. It is shown that the VSC limited reactive support and suppressed negative sequence current affect fault detection, forcing the relay to malfunction. The results of this paper can be used as a reference for understanding the effects of VSC-HVDC system on the operation of the distance protection during faults.     

A digital distance relay using negative sequence current

The configuration and performance of a recently developed digital distance relay using negative sequence current for remote backup protection are described. Since relays for remote backup protection are designed for remote faults, the fault current that is input to the relay is small due to the influence of current distribution factors. This in turn makes the relay sensitive to the effects of load current. In order to resolve this problem, a distance relay using negative-sequence current has been developed and put into use. The characteristics of this relay are: (1) the effects of load current are reduced, so the relay rarely maloperated due to load current during a fault; and (2) the hardware configuration of a digital relay that performs calculation on a negative component is simple and thus relatively error-free     

一起串联补偿线路跳闸故障的分析

针对某超高压500 kV串补输电线路因选区偏转而引起的三相跳闸事故,探讨了故障时串补保护和线路保护的动作行为。搭建与实际一致的仿真模型,代入现状运行方式下的具体参数,通过RTDS对模型进行数字模拟实验,分析发现,其保护动作行为符合设计原理和录波数据,当系统仅发生单相经过渡电阻故障,且串补仅B相MOV暂态导通时,选区确实会发生偏转,造成2套线路保护选相不一致,扩大事故范围。结合实例,深入研究串补是否投入情况下单、双回运行线路的单相接地故障,得出零、负序电流选区出现误选的条件,并给出可行的解决方案。     

Detection of Symmetrical Faults by Distance Relays During Power Swings

For maintaining security of distance relays, power swing blocking is necessary to prevent unintended operation under power swings. To be dependable, distance relays must operate whenever a fault occurs. Therefore, detecting faults during power swings is an important issue since the relay should be able to differentiate the fault condition and not be blocked during that time. This paper presents a new method for detecting a symmetrical fault during a power swing, based on extracting components of the current waveform using the Prony method. The merit of the method is demonstrated by simulating different faults during power swing conditions using the Alternate Transients Program version of the Electromagnetic Transients Program.     

高压输电线路距离保护克服过渡电阻能力研究

高压输电线路中存在较大的过渡电阻,很容易引起距离保护拒动或误动.分析特高压单侧电源经长线路出口故障和双侧电源长线路出口故障时过渡电阻对距离保护工作的影响,探讨单侧电源助增电流网络、外汲电流网络中过渡电阻对测量阻抗的影响,并给出2种网络结构在不同地点处保护测量阻抗的计算公式.研究能较好躲过渡电阻特性的零序电抗继电器、自适应接地距离继电器、神经网络距离继电器,分析比较不同方法的优缺点及适用场合.     

大型风电场对工频故障分量距离保护影响的研究

随着风力发电技术日趋成熟,越来越多的大型风电场开始投入运行。由于风电场运行方式的变化及其弱电源特性,会对输电线路的保护造成一定的影响。研究了工频故障量距离保护的基本原理及风电场运行方式的多变性,并在此基础上进一步分析了风电场的运行方式的变化和弱电源特性对保护的影响,通过利用电压相量图分析保护判据的比相表达式提出了对传统距离保护的改进。通过分析可知,在发生金属性故障时,工频变化量距离继电器几乎不受风电场运行方式的影响,但由于风电场正、负序等值阻抗较系统阻抗大,使得相间保护耐受过渡电阻的能力很小,而受风电场零序阻抗较大的影响,接地保护耐受过渡电阻的能力较强。以Matlab/Simulink为平台建立了风电场并网的仿真模型,研究了风电场对保护的影响及对比保护改进前后在故障时的动作行为,仿真结果与理论分析相吻合。     

Realistic insights into impedance seen by distance relays of a SSSC-compensated transmission line incorporating shunt capacitance of line

In practice, the series compensation is applied to medium-/long-length transmission lines. Such lines include significant shunt capacitance, neglecting of which is expected to noticeably influence the impedance seen by distance relays. Taking the shunt capacitance of a transmission line compensated by the static synchronous series compensator (SSSC) as well as other affecting factors into account, this paper derives precise mathematical expressions governing the apparent impedance seen by the distance relay of the line. Through the acquired expressions, the research conducts sensitivity studies considering different compensation scenarios and locations for the SSSC. The studies make an attempt to produce realistic insights into ideal tripping characteristics of the distance protection of the under studied line, and also into the susceptibility of the impedance seen to output parameters of the SSSC. In addition, the research’s findings well demonstrate the extent to which neglecting the shunt capacitance of the line would contribute to mis-operation of the distance relay.     

SSSC对阻抗继电器动作特性的影响分析

将SSSC安装于线路中点,根据SSSC在故障范围之内和之外2种情况,对阻抗继电器的测量阻抗进行了分析,且通过SSSC的不同注入电压和补偿方式,以及过渡电阻的变化,仿真了阻抗继电器的动作特性。结果表明,SSSC在故障范围之内时对阻抗继电器的测量阻抗产生了很大的影响,应该采取措施减小SSSC对阻抗继电器的影响;另外,过渡电阻的影响同样不可忽略。     

A novel digital distance relaying technique for transmission lineprotection

Parallel transmission lines often pose more difficult protection problems than single lines. In the case of parallel lines, a number of problems arise when using the distance protection. The paper discusses problems associated with parallel line distance relaying schemes and presents a novel technique to overcome these problems. Two relays instead of four are proposed for the double lines, One relay is located at the beginning and another one at the end. Each relay is fed by three voltage and six current signals from the two lines. The suggested technique is based on the comparison of the measured impedance of corresponding phases. So, the complexity of the possible types of faults, high path fault resistance, mutual effects, current in-feed, inter-system faults are solved. Moreover, 100% of line is protected and the problem of balance-point locations is avoided. Alternative Transient Program models the power system and simulates different fault conditions     

变压器相间后备保护的改进

目前变压器相间后备保护对变压器匝间故障的灵敏度不高。低压过流保护的灵敏度不高是由于少匝数匝间短路时变压器电压下降很少。负序电流继电器的动作与电压的降落无关，因而可以获得较镐的灵敏度，距离继电器应用于变压器时其性能受Y，d接线变压器两侧电位移的影响。负序距离继电器的行为与变压器绕组的接线无关，所以它是作为变压器后备保的距离继电器的最佳选择。文中不仅讨论了负序电流和负序距离继电器的优越性能，而且提供了防止这两类继电器在电流断线和电压断线时发生误动的方法，从而得到了一个既灵敏又安全的改进的变压器后备保护。     

陕西电网330 kV“12.5”主变故障差动保护动作分析

详细分析陕西电网330kV"12.5"主变压器故障时差动保护装置的故障电流波形和数据,梳理主变区内、外故障的实际过程,研究主变内、外部故障特征和差动保护在区内、外转换复杂故障情况下的动作行为,查明保护动作原因,对变压器差动保护原理提出改进意见和建议。指出国产变压器抗短路能力不能满足IEC和国标的抗短路水平要求,建议主变制造厂家优化主变的结构和制造工艺,提高主变的制造质量。     

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.