A busbar protection technique and its performance during CTsaturation and CT ratio-mismatch

This paper describes a digital technique for protecting busbars. The technique uses positive- and negative-sequence models of the power system in a fault-detection algorithm. While phase voltages and currents are used to detect faults, parameters of the power system are not used. An analysis of the performance of the proposed technique during CT saturation and ratio-mismatch conditions is presented. The performance of the technique was investigated for a variety of operating conditions and for several busbar configurations. Data generated by EMTP simulations of model power systems were used in the investigations. The results indicate that the proposed technique is stable during CT saturation and ratio-mismatch conditions     

A power transformer protection technique with stability duringcurrent transformer saturation and ratio-mismatch conditions

This paper describes a digital technique for protecting power transformers. The technique uses positive- and negative-sequence models of the power system in a fault-detection algorithm. While phase voltages and currents at the transformer terminals are used to detect a fault, no information concerning parameters of the transformer and power system is required. The performance of the proposed technique was studied for a variety of operating conditions using data generated by EMTP simulations. The impact of ratio-mismatch and saturation of current transformers on the performance of the technique was also examined. Results indicate that the proposed technique is stable during these conditions     

Hybrid linearization of a power system with FACTS devices for a small signal stability study: Concept and application

This paper deals with a hybrid linearization method of a power system with flexible AC transmission system (FACTS) devices. The linearized power system model provides useful information, which is necessary for the small signal stability study and the controller design. Although the algebraic linearization method provides an accurate and parameterized linear system, it may incur computation burdens for the large power system especially with multiple FACTS devices. The numerical identification of linearized system by utilizing input–output numerical data is highly versatile. However, quite amount of valuable information may be not fully utilized. In this paper, a hybrid method in which the algebraic and the numerical linearization technique are combined is presented. While both the power system and the FACTS devices are separately linearized by using algebraic method, the interaction terms between the power system and FACTS devices are numerically identified by adopting the quadratic optimization technique. The proposed hybrid linearization technique is tested on the WSCC system in which one thyristor-controlled series capacitor is installed. Both eigenvalue analysis and time-domain simulation results verify that the proposed method can effectively identify the linearized model of the power system with FACTS devices.     

计及多状态元件模型的系统状态快速排序技术

在实际电力系统中,由于元件的停运概率不同,一些高重故障会比低重故障的发生概率大。这些大概率高重故障状态的数量多,且对系统可靠性的影响大。而在可靠性评估中,状态枚举法通常采用截止故障重数进行状态筛选,会忽略掉这些大概率高重故障事件。文中提出计及多状态元件模型的快速排序技术,基于元件异常状态序列与相邻系统状态,能够按照概率从大到小依次选取系统状态,直至满足评估精度或数量要求。与直接选择法相比,计算效率优势十分明显。由于该方法能够选出大概率高重故障状态,因此,与截止故障重数方法相比,该方法只需少量的系统状态就可获得较高的评估精度。最后以IEEE-RTS为算例验证了该结论。     

基于组件技术的潮流计算软件的研究与实现

首先分析了目前传统电力软件系统中存在的缺陷与问题,如基础计算功能重复开发,不利于升级与维护,软件开发较复杂。其次分析了组件技术在解决这些问题上的独到之处,并提出采用组件技术来实现电力系统基础计算软件。接着介绍了基于J2EE的软件开发方法和软件开发的具体过程,说明了J2EE体系结构是适合于电力系统软件开发的方案。并利用J2EE的EJB技术实现了一个通用的潮流计算软件。该软件采用了许多稀疏技术,如稀疏导纳矩阵的存储和稀疏矩阵的因子表分解等。最后以IEEE系统14节点网络为例对软件进行了测试,收敛性和计算速度均达到要求,与BPA相比,误差在允许范围内,通过实例验证了软件的独立性、正确性和对电力系统应用软件体系结构改进的可行性。     

A new transmission line fault locating system

The paper describes a new fault locating system that has been developed at Mehta Tech, Inc (USA). The distance calculating technique of the system is based on the reactance method of fault distance estimation, using data from one terminal of a transmission line. The technique compensates for errors caused by factors such as load flow and fault resistance. The system has been in commercial use by some reputable electric utilities, both local and international for over three years. The paper also presents some field results that have been obtained from some of these electric utilities that are using the new fault locating system     

Interconnected multi-machine powersystem stabilizer design using whaleoptimization algorithm

The role of Power System Stabilizer (PSS) in the power system is to provide necessary damping torque to the system in order to suppress the oscillations caused by a variety of disturbances that occur frequently and maintain the stability of the system. In this paper, a PSS design technique is proposed using Whale Optimization Algorithm (WOA) by considering eigenvalue objective function. Two bench mark multi machine test systems: three- generator nine- bus system, two- area four- generator inter connected system working on various operating conditions are considered as case studies and tested with the proposed technique. Extensive simulation results are obtained and effectiveness of proposed WOA-PSS are compared with well - known PSO and DE based stabilizers under several disturbances.     

A new stabilizer design technique for multimachine power systems

A simple and systematic procedure for decentralized stabilizer design for multimachine systems is presented in this paper. The procedure first selects the most effective location of a stabilizer according to a machine stability index. The parameters of the stabilizer are then determined by a decentralized feedback control scheme. This process is carried out for one stabilizer at a time. The resultant overall improvement of the system stability, measured by a system stability index, is used to decide how many stabilizers are required for the system. The proposed technique is illustrated by a test system. Both eigenvalue analysis and nonlinear simulation are performed to investigate the effectiveness of the technique.     

Applying a robust control technique to damp low frequency oscillations in the WECC

This paper demonstrates the application of a robust technique for damping low frequency oscillations in the WECC. The control is designed by extending the logic of SMA and integrating it with the LMI technique to develop a single-gain feedback controller that is capable of damping oscillations in large systems. It is an integrated form of control because it combines different controllers together so as to prevent any negative interaction between the individual controls. The proposed technique is initially applied to an equivalent model of the WECC system developed in MATLAB and then transferred to a larger and more detailed version created in PSLF. The controllers initially used for the design are the two HVDC lines and an SVC. Three ESDs are added to the model for the improvement of the control. The results indicate that the technique proposed in this paper provides adequate damping to the relevant modes of oscillations and that it can be easily applied to large and complex power system networks.     

A DIAKOPTICAL TECHNIQUE FOR SHORT CIRCUIT STUDIES OF LARGE SIZE POWER SYSTEM NETWORKS

ABSTRACT

The paper presents a diakoptical technique for deriving the impedance matrices required for short circuit studies of large size power system networks by tearing the system into smaller subsystems by cutting appropriate tie lines. The bus admittance matrix is formed for the sequence networks of each subsystem and then modified later by means of diakoptics. The simulation of mutual couplings is taken into account in the zero sequence networks. Only columns of the impedance matrices corresponding to the faulted buses are computed in the proposed technique which is based on factorized bus admittance matrices and full exploitation of sparsity. The proposed technique can either be used in a single–processor computer for sequential solution of torn subsystems or in a multicomputer configuration for a faster solution by parallel processing of torn subsystems. Both symmetrical and unsymmetrical faults are studied by using the proposed technique which produces exact results as the untorn system. No iterative calculations are required as short circuit analysis is basically a linear problem. Included in this paper is a numerical example of a sample test system.     

卫星通信多址接入方式的比较和分析

在卫星通信中常用的射频多址接入方式，有TDMA、FDMA和CDMA。射频多址接入技术主要解决不同地理位置上的地球站信号如何共用一个卫星转发器问题。文中主要就应用这三种多址技术的卫星通信系统的容量计算和系统利用效率分别进行了详细的讨论和分析，并指出，在占用相同转发器带宽条件下，TDMA系统容量和效率最高。还指出努力提高效率和容量是CDMA系统的关键。     

A generalized probabilistic cost of service allocation approach forgeneration and transmission facilities

The authors present an integrated approach for cost of service allocation of generation and transmission facilities which utilizes a probabilistic technique similar to that used by many utilities for system planning. The procedure for composite system cost of service allocation is presented. The use of the loss of energy expectation index is extended from generation capacity studies to composite generation and transmission system cost of service allocation. The technique is demonstrated by application to the IEEE Reliability Test System (IEEE-RTS). The results obtained by applying selected methods to the IEEE-RTS are illustrated and compared     

Energy efficient nonfragile control protocol for nonlinear large-scale systems with input quantization

The problem of robust stabilization for a class of nonlinear large-scale systems with the energy constraints and time-varying actuator faults is addressed in this article. In the considered system, the stabilization criteria is achieved via a sensor-network-based distributed fault-tolerant controller. Moreover to limit the consumption of energy by the sensors, the measurement size reduction technique and communication rate reduction approach are implemented such that the resulting closed-loop system is stable within a predefined extended passive performance index level. In particular, the sensor signal quantization technique is used to reduce the frequency and size of the transmitted data packet in the communication sequence. Based on the switched system theory and Lyapunov approach, a new set of sufficient conditions is obtained in the form of linear matrix inequality constraints to ensure the exponential stabilization of the considered system. The developed fault-tolerant resilient control gains are designed by resorting to the cone complementarity linearization algorithm. Moreover, a nonisothermal continuous stirred-tank reactor with interconnection is considered as an example to demonstrate the effectiveness of the proposed design technique.     

采用差频技术的正弦调制型微波测距系统研究

针对目前无线定位中单点测距精度较低的问题,提出一种基于差频技术的正弦调制型微波测距方法;该方法采用有源反射式目标点实现远距离的测距,采用差频测相技术实现系统的高精度测距,采用基于时间数字转换器(time-to-digital converter)的时间差模块实现高精度相位测量;采用现有商业化器件搭建了实验系统并进行了测距实验研究,大位移试验中该系统的测距线性度约为0.999 9,小位移实验中测距精度约为2.86 cm,分辨率优于10 cm。     

Fast evaluation of available transfer capability using cubic-spline interpolation technique

This paper presents a new computationally fast and accurate method for evaluating available transfer capability (ATC) based on a curve fitting technique so-called as the cubic-spline interpolation technique. The advantage of the technique used in the computation of ATC is that it has the ability to reduce the time consuming ac power flow computations. The cubic-spline interpolation technique traces the curves of voltage magnitude and power flow variations with respect to the increase of real power transfer. ATC is then determined at the point where the voltage or power flow limits intersect the curves. Prior to the ATC evaluation, contingency ranking and selection techniques are used to define the critical lines in a system that can adversely affect the transfer capability assessment. The effectiveness of the proposed method is verified by illustrating the ATC evaluation on a practical test system. ATC results obtained from the proposed cubic-spline interpolation technique prove that the method is satisfactorily accurate and it is faster than the ATC method using the recursive ac power flow computations.     

Computation of Transient Probabilities of Electric Power Plants

To find the transient probabilities that reflect the behavior of a large electrical power system or of any other system, a suitable technique is required. Before calculating the transient probabilities for the overall electrical power system, which consists of a number of subsystems (such as generators), the failure and repair rates of each generator need to be defined. These two coefficients can form a transition rate matrix, which represents each subsystem. To form the overall system, a special technique is required. In the present study, the Kronecker technique is used to form the overall transition rate matrix, which represents the whole system. Forming the overall system is the first part (major part) of the current study. The second part is to find the transient probabilities, following the fourth-order Runge-Kutta method. Two examples for the State of Bahrain are carried out. One of the advantages of the Kronecker method is its simplicity in programming. In addition, by applying the new technique under investigation, the system behavior of both electric power plants can be identified.     

Decentralized model predictive‐based load‐frequency control in an interconnected power system concerning wind turbines

This paper presents a load‐frequency control (LFC) design using the model predictive control (MPC) technique in a multi‐area power system in the presence of wind turbines (WTs). In the studied system, the controller of each local area is designed independently such that the stability of the overall closed‐loop system is guaranteed. A frequency response model of the multi‐area power system including WTs is introduced, and physical constraints of the governors and turbines are considered. The model was employed in the MPC structures. Digital simulations for a two‐area power system are provided to validate the effectiveness of the proposed scheme. The results show that with the proposed MPC technique the overall closed‐loop system performance shows robustness in the face of uncertainties due to governor and turbine parameter variation and load disturbances. A performance comparison between the proposed controller with WTs and MPC without WTs and a classical integral control scheme is carried out, confirming the superiority of the proposed MPC technique with WTs. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An on-line relay coordination algorithm for adaptive protectionusing linear programming technique

An adaptive system for protecting a distribution network should determine and implement relay settings that are most appropriate for the prevailing state of the power system. This paper presents a technique for determining coordinated relay settings. The technique uses the Simplex two-phase method; Phase I determines whether the constraints selected for illustrating the conditionality between primary and back up relays are feasible, and Phase II finds the optimal relay settings. A looped distribution system, protected by directional overcurrent relays, was used for testing the technique. The tests were conducted in a laboratory environment; some results from those tests are reported in the paper     

面向对象技术在调度员培训系统中的应用

本文介绍了一套采用完全面向对象的概念及编程技术开发的调度员培训系统。将电力系统的元件以对象来表示,将仿真中的特定应用也作为一个个独立的大对象来处理,对象之间以事件来驱动,创建了一个协调统一的面向对象的开发环境。     

基于Internet/Intranet技术的SCADA/EMS设计

为进一步提高当前SCADA系统的实时性、灵活性和扩展性,在分析了IT技术发展、Internet普及范围及电力系统对SCADA系统新要求的基础上,结合当前流行的三层结构技术、P2P计算模型及广域服务器集群技术等,提出了基于Internet/Intranet技术的SCADA/EMS系统的构想、具体结构、通信模型及应采用的一些相关技术。此外,为提高原有设备的利用率,也提出了通过增添网关设备来将传统SCADA改造成基于Internet技术的SCADA系统的方法。对两种SCADA系统的成本效益分析结果表明新型系统的性价比良好。