Charge comparison protection of transmission lines-communicationsconcepts

The authors present the basic concepts of a digital approach to the communications requirements of a new transmission line protection scheme. Charge comparison is a new transmission line protection system. It compares local and remote quantities of charge, using a bidirectional communications channel. Charge comparison is a form of current differential relaying. Traditional current differential relaying schemes have three critical communications-related problems: protection is lost if the channel fails, a large channel capacity is required, and precise channel delay compensation is required. In large measure, charge comparison overcomes these three communications-related problems     

Applying CTs with digital ground relays

Industrial power distribution system substation transformers and generator step-up transformers in power stations often use resistance-grounded wye secondary windings for medium-voltage power distribution. The purpose of this is to limit damage due to ground-fault currents, while providing sufficient fault current for the operation of ground-fault relaying. The relaying used to protect against ground faults in the system may not provide sufficient protection of the transformer winding against internal faults because the backup ground overcurrent relay in the transformer neutral-to-ground connection must be set to coordinate with downstream relays. In order to protect the winding itself, special relays are utilized. Ground differential protection can be provided by digital overcurrent relays in conjunction with auxiliary ratio matching transformers. Ground differential protection can also be provided in multifunction digital relays. Transformer protection relays may include this feature with one of the schemes used with component relays. If a feeder-protection relay is used on the secondary, in some cases, this may have a ground-directional feature that can be utilized for ground-differential protection     

超高压线路纵联保护配置方案

根据目前电力通信系统状况和线路保护的设备水平，阐明了用于超高压线路纵联保护传输信号的通信方式，例如载波、光纤及微波通道等，针对这些不同的通信方式的保护形式进行选择分析后认为，在考虑220kV及以上电压等级的线路纵联保护方案时，保护信号传输通道应首选复用数字通信电路，逐渐淘汰载波通道，保护形式应首选分相电流差动保护；允许式方向或距离保护复用通信通道，经RS－232串行口与通信终端连接，其起止式异步传输方式值得借鉴。     

An open-system approach to power system protection and control integration

Data packets based high-speed digital communications have opened the door for new types of applications in power system protection and control. The main obstacle in adopting Ethernet-type networks for time-sensitive communications was the data transfer characteristic of these networks. With baud rates in the gigabit-per-second range, the industry has started adopting the Ethernet networks as a viable alternative, not only because of their lower cost. This paper presents an open-system approach in which protective hardware equipment is designed to work in a clustered environment, sharing resources, data, and diagnostic functions with similar units. The Ethernet network, being capable to accommodate transparently a wide range of protocols, is used to connect the protective hardware. A model was developed for the Ethernet network to be incorporated into the power system simulation. The characteristics required from a digital relaying algorithm to be able to work with signal samples sent across data packets based networks are described in this paper. The proposed solution is implemented using a modified adaptive least-square-error algorithm and tested on a protection system that was integrated into the power system model.     

An adaptive scheme for digital protection of power transformers

The development of an adaptive scheme for digital differential protection of power transformers is described. The transformer status is monitored to decide if the transformer is disconnected or is in normal operating condition. When the transformer is energized, a two-state Kalman filter model monitors the transformer during normal operating conditions. The current transformer ratios and tap values are included in the algorithm to obtain an adaptive percentage differential characteristic. This adaptive scheme was tested on data obtained in the laboratory and proved to be highly accurate and fast     

数字—物理模型互联方法及混合仿真系统稳定性研究

现代电力系统通常包含高压直流输电(HVDC)或灵活交流输电(FACTS)等由开关器件构成的高频元件,单一实时数字模型因其离散性而受仿真截止频率限制,无法准确模拟这类元件的高频响应过程,目前最有效的仿真措施是建立包含这类高频元件物理模型的数字-物理互联混合模型.根据电路替代定理提出节点电压重叠互联方法,即在数字模型中将接口点电压变量通过D/A转换输出通道形成物理模型中的电压源替代支路,又将该物理支路的电流变量通过A/D转换输入数字模型中形成接口支路的替代电流源,从而实现数字一物理模型的互联;从系统稳定性的角度对基于该方法互联的混合仿真模型进行了理论分析,证明混合仿真模型为有条件数值稳定系统且推导出模型的稳定条件判别式;最后,通过混合仿真实验验证了理论分析结果的正确性.     

线路纵差保护同步采样基准端的自动确定方法

首先介绍了目前确定采样基准端的两种方法:人工设定和自动确定,然后提出了一种完全基于数据通道的采样基准端的自动确定方法,并详细介绍了该方法的具体实现。该方法物理意义明确,具有实现简单、可靠实用的特点,已经过保护装置的实际验证。     

Protection and commissioning of multifunction digital transformer relays at medium voltage industrial facilities

The application of multifunction digital relays to protect medium voltage power transformers has become a common industrial practice. Industrial transformers, unlike utility transformers, frequently use neutral grounding resistors to limit ground current during faults to the 200-400-A level on medium voltage systems. This paper will discuss why these types of transformers require sensitive ground differential protection. The paper will also discuss the basics of transformer protection including phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, current transformer (CT) requirements, and harmonic restraint, and communicating these properly to new digital relays. The rationale for providing transformer overexcitation protection on all major transformers within mill facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address increasingly more transformer winding configurations. This has resulted in digital transformer relays requiring an Einstein to set and an Edison to commission. Since there are few Einsteins or Edisons among us, the next generation of transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital transformer protective relays.     

A new digital directional transverse differential currentprotection technique

Recently, several papers have discussed the protection of parallel transmission lines connected to common buses. The main purpose of this paper is to discuss problems associated with parallel line relaying schemes, which depend upon the theory of transverse differential protection relaying, and to present a new advanced technique to overcome these problems. The suggested technique relies on current incremental signals in corresponding phases instead of current magnitude. This method eliminates many of the associated problems typically encountered in this area. The possibility of applying the suggested technique on parallel three-terminal power transmission lines was investigated and satisfactory results were recorded. The voltage signal and the communication channel have been excluded from this study     

A Kalman filter based digital percentage differential and groundfault relay for a 3-phase power transformer

The design and real-time implementation of a Kalman-filter-based digital percentage differential and a ground-fault protection scheme for three-phase power transformers are presented. A set of eleven-state Kalman filters is used to estimate the fundamental and up to fifth harmonic components of the transformer current signals. The protective relay is equipped with an even harmonic restraint during magnetizing inrush conditions and a fifth harmonic restraint during overexcitation conditions. The restraint during external faults is provided by means of a percentage differential characteristic. The relay operates in half a cycle during internal faults. In order to achieve sensitive ground-fault protection, separate primary and secondary ground-fault protection are provided. The relay algorithm is implemented on a single TMS320 digital signal processor and tested in real time using a three-phase laboratory power transformer     

数字差动保护抗电流互感器饱和的线性区方案

主设备保护通常采用差动原理作为主保护原理,随着数字保护在电力系统的广泛应用,存在电流互感器（TA）暂态饱和易引起差动保护误动的问题。数字差动保护抗TA饱和的线性区方案是建立在TA暂态饱和时一次电流每个周期过零时始终存在一定的线性传变区域的理论基础上,对TA传变的数据取最小的线性区选择方法,动作电流采用半波傅里叶滤波算法计算,制动电流采用全波傅里叶滤波算法计算,构成比率制动差动保护。该方案原理简单、实现方便,动模录波数据说明该方案能够基本消除区外故障TA暂态饱和引起差动保护误动的情况,可直接应用于变压器差动保护、发变组差动保护和母线差动保护,应用前景良好。     

220kV高压电网继电保护配置

为保证系统运行稳定,分析了220 kV高压电网线路采用双光纤通道保护方案:配置1套光纤电流差动和1套光纤距离(方向)保护。考虑电网结构、系统稳定、供电可靠等诸多因素,以分相电流差动保护与纵联距离保护作为两套主保护,以三段式接地距离和相间距离保护与零序电流保护作为后备保护,基本达到了工程要求。     

Coding techniques for secure digital communications for unitprotection of distribution feeders

The dramatic growth in new designs of microprocessor relays has led to a growth in the use digital communications for protection. Unfortunately in any communication system there will always be some corruption of the received data. Part of the art and science of relay design is therefore to take this into account. This paper examines coding techniques designed to minimise the probability of corrupted data being declared as healthy. Message size, coding techniques and interleaving are examined with respect to the choice of a coding strategy for a secure data communication system for unit protection     

SIEMENS 7UT51型数字式差动保护继电器中差动保护的整定计算

介绍SIEMENS 7UT5 1型数字式差动保护继电器中的差动保护部分的特性 ,详细分析该保护的整定计算原则 ,并将其应用在扬二厂的厂用电系统整定计算中     

Modal saturation detector for digital differential protection

A new digital method for the rapid and reliable detection of current transformer saturation for single- and multiple-pole short circuits is described. The function principle is independent of the number of phases involved in the short-circuit and independent of the magnetic properties of the current transformers, including remanance. In order to achieve this, the secondary currents of the three phases are transformed into space phasors with a blocked backward rotating component. In the unsaturated state their trajectories are circles. The deviation from this characteristic form, and hence the inception of current transformer saturation, can be detected in less than 3 ms. One result of quick detection is that the differential protection can be adjusted to higher sensitivity than in known protection devices. This guarantees reliable operation even in the case of short circuits with weak short-circuit currents. The new modal saturation detector is equally suited for the differential protection of power lines as well as busbars and other circuit arrangements     

New approach to the design of digital algorithms for electric powermeasurements

Digital algorithms for electric power measurements are represented as 2-D digital finite-impulse-response (FIR) filters applied on voltage and current samples. Based on this approach, a novel technique for algorithm design is developed. The technique provides a convenient way to design new algorithms for measuring the electric power components according to various definitions in both sinusoidal and nonsinusoidal conditions. Several new algorithms are derived by using the proposed design technique. The existing algorithms for power measurements are also derived by using the new approach. The algorithm performance was tested using actual signal recordings     

The evaluation of frequency properties of digital measuring element reacting to increment vector current values

The frequency properties of a digital measuring element can be used as criteria for the selection of operating values of the numerical distance protection starting element of power-swing blocking. The conditions of the selection of the operating values of the starting element of power-swing blocking usually ensure sensitivity to short circuiting. The primary function of the starting element is blocking the distance protection from power swings and out-of-step conditions, based on the fact that the rate of current change and its increment for electromechanical processes are much lower than for a short circuit. Mathematical modeling of the digital measuring element based on filter Fourier and FIR algorithms with confirmation of the results by using a computer-controlled testing system allows criteria to be obtained that reflect the physical nature of the processes that can be used when selecting the settings of the starting element of power-swing blocking. An approach to selection of the settings of a digital measuring element of relay protection that is responsive to the current increment, based on analysis of digital signal processing algorithms, allows one to determine the criteria for the detuning of the emergency operation, taking into account the frequency deviation, the impact of the presence of a transient dc component, and the higher harmonics. The frequency properties of the digital measuring element reacting to increment vector current values can be used to determine the threshold detuning from power swings and out-of-step conditions as additional conditions for selecting settings of the starting element of power-swing blocking, which will increase the sensitivity of the distance protection for short circuits and the reliability of detuning from power swings and out-of-step conditions.     

IEEE1588 V2在全数字化保护系统中的应用

通过分析IEEE1588 V2的特点,提出了支持IEEE1588 V2同步标准的全数字化保护系统组网测试方案。该方案针对网格型接线变电站的数字化保护系统设计,选用保护智能电子设备,建立网格角母线保护柜、馈线差动和距离保护柜、变压器高压/低压侧保护柜;提出以太网交换机的过程层应用方案,利用保护测试仪的时间码转换接口与上述以太网交换机配合完成时间同步。冗余时间源机制提高了过程层采样值时间同步的可靠性和准确性。     

基于Matlab的计算机距离保护微分方程算法仿真与研究

运用M atlab完成电力系统计算机距离保护的仿真,应用了两种基于线路模型的解微分方程的阻抗算法,分析了其应用于不同参数线路时的适应性,并通过分析在考虑存在干扰和误差时的阻抗计算结果,对两种算法的稳定性进行了研究。还对这两种算法的工程应用提出了有益的建议。     

继电保护光纤通道仿真测试及研究

随着光纤电流差动保护在电力系统中的广泛应用,实际运行中暴露出越来越多的新问题,其中由于缺乏针对光纤通道的各种误码工况的仿真测试及试验,光纤电流差动保护在通道延时、误码工况下的动作行为和动作性能没有办法进行试验和验证,针对光纤电流差动保护应用的实际情况设计出了仿真测试装置,并介绍了其实现功能、硬件设计和应用。