Recognition of coherent swing in power systems and detection of step-out using power and current measured on tie lines

When a fault occurs in a large interconnected power system, several generators may swing coherently and form a group. Loss of synchronism may occur among groups of these generators. In order to develop a stabilizing control system, two new methods are proposed in this paper. The first method is to select generators which swing coherently. The method uses a new index that is based on the physical relation: when two generators swing coherently, the phase angle of a generator terminal voltage increases when the angle of the other generator increases, and decreases when the other decreases. To detect a loss of synchronism, the power P and current I measured on a line with the interval of a certain time period are used. By using this method, the position of the operating point of power system after disturbance on the power angle curve can be estimated. This means that the degree of stability can be observed with a small number of observations measured on a line. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(4): 22–31, 1997     

Development of an on-line stabilization method for local power systems with large-capacity generation plants

This paper presents an on-line stabilization control method developed with the aim of maintaining transient stability in a local power system which includes large-capacity generation plants. The characteristics of this method are that the power/angle curve is estimated from the on line active and reactive power measured at the generator terminal, and the optimum generation shedding for stabilization is determined by applying the equal area method to this curve. Simulation tests using detailed models of the power system confirmed that the optimum generation shedding for stabilization could be computed for various fault conditions, both symmetrical or asymmetrical. It was also determined that the on-line data could be sampled for several tens of milliseconds after clearing the fault. Thus, this method provides effective control logic for practical stabilizing systems.     

Stabilizing control, system preventing loss of synchronism fromextension and its actual operating experience

This paper presents a stabilizing control system that was implemented to the power system of Tokyo Electric Power Company and worked successfully, shedding the minimum number of generators and preventing the extension of loss of synchronism to the other generators when a severe fault occurred on May 22, 1992. The stabilizing control system measures voltage and current at the rate of 600 Hz, predicts the change of phase angles of generators and decides the minimum number of generators to be shed for stabilization when instability is predicted and sheds them     

Fast generation shedding equipment based on the observation ofswings of generators

A novel method and recently developed stabilizing equipment to prevent the loss of synchronism of generators in pumped-storage plants due to spreading are presented. The method includes functions to estimate the swing of each generator by using online generator output sampled 600 times per second after an occurrence of a disturbance (such as a fault, faulty equipment, etc). Generator swing 200-300 milliseconds ahead and loss of synchronism between generators in pumped-storage plants and those in thermal and nuclear plants can be predicted 200-300 ms ahead, and the number of generators that must be shed to maintain stability can be decided     

Development of transient stability controller system (TSC) based on on-line stability calculation

A new transient stability controller system (TSC) based on on-line transient stability calculation has been developed. The TSC system prevents the power system from wide-area blackout by shedding generators optimally when a serious fault occurs. This system consists of a central processing unit (TSC-P), and four local units for fault detection (TSC-C), and seventeen units for generator shedding (TSC-T). The TSC-P selects optimal generators to be shed for stabilization based on on-line transient stability calculation for contingencies at 500 kV lines and buses every five minutes. The results are transmitted to the TSC-Cs periodically. Should any fault occur, only one TSC-C will detect the fault occurrence and send control signals to the TSC-Ts which actually generate shedding signals. To realize the TSC system, essential are fast stability evaluation methods for a large number of contingencies and effective selection methods of optimal generators to be shed for stabilization. This paper presents total algorithms applied in the TSC-P, the results of algorithm verification tests using a prototype system combined with a large-scale analog simulator, and the characteristics of the actual system.     

Improvement of power system stability by high-speed power control of adjustable speed machines

Large-capacity adjustable speed machines (ASMs) at pumped storage power stations have been put into full operation and their operating characteristics have been highly evaluated from the viewpoint of power system operation. The output power (input power) of ASMs can be controlled very quickly by applying a vector control scheme to the excitation control. This quick responsive feature of ASMs can make it possible to improve the stability of the neighbor subpower system. For improvement of transient stability, the output power of ASMs is reduced very quickly in order to control the acceleration of neighbor generators during and after transmission line faults. For improvement of dynamic stability, the output power of ASMs is modulated in accordance with the stabilizing signals detected from the swing of generator rotor or the power flow fluctuation on the transmission line. This paper describes the design concepts and method of control system for improving the transient and dynamic stability and proposes a power system stabilizing control system. The effects of the proposed stabilizing control system have been verified by a power system simulator. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(2): 27–36, 1997     

Coordinated stabilizing control for large-scale interconnected power systems,by superconducting magnetic energy storage unit and power system stabilizers

The purpose of large-scale power system interconnection is to achieve extremely economical and reliable power generation and transmission. It has established the present power systems of high quality. On the other hand, in the large power systems with complex configuration, an undamped power swing with low frequency caused by the synchronous power between interconnected systems tends to occur as well as an undamped power swing caused by the synchronous power of specific generators. Several coordinated stabilizing control schemes for the power systems by sets of power system stabilizers (PSSs) have been investigated so far. PSS is very effective for the stabilization of power swing among a few specific generators because the function of PSS is achieved by the voltage control using the generator field winding circuit. However, it seems that PSSs do not have sufficient ability to stabilize the power swings between interconnected systems. In this paper, the superconducting magnetic energy storage (SMES) which is significantly effective for the power swings between interconnected systems is introduced and a coordinated power system stabilizing control by SMES and PSSs is proposed. The advantages of the proposed control scheme are: 1) high efficiency of the controller by the distribution of functions; 2) independency of the control design for PSS and SMES; and 3) robustness of the controller, and so on.     

快关汽门与励磁的协调控制增强发电机组暂态稳定

某些严重的电力系统故障，例如在电厂附近发生的短路故障，会导致整个系统暂态稳定的丧失。为此经常切除部分机组来防止非同步运行，但是这种增强暂态稳定的方法将干扰整个系统的功率平衡，并且需要经过很长的调整时间才能建立起新的稳态运行状态，本文介绍了一种避免切机的新方法，通过协调快关汽门和励磁控制来实现发电机组的稳定运行，领导具计算表明，经过1到2个非同步周期就可以建立新的稳定状态。     

A new method for detecting loss of synchronism using power andcurrent measured on a line

When a fault occurs, coherently swinging generators form one group and the remaining ones form another. If the fault is severe, loss of synchronism may take place between groups after single or multiple swings. This paper proposes a new method for detecting loss of synchronism. With this method, power and current are measured at regular intervals on a tie-line linking sub-networks to which groups of generators belong. Changes in power and current are calculated during the interval, the location and direction of the operating point of the power system moving on the curve of power versus phase angle is estimated and the loss of synchronism is detected. The validity of the method is shown by simulations using model networks     

基于广域测量系统的快速暂态稳定预测方法

在运用相量测量单元实测系统故障时轨线的基础上,采用一种在机器人领域广泛应用的抓球算法,对电力系统故障后预判失稳的发电机转子角进行预测.该方法分为跟踪和预测2个阶段:首先应用粒子群优化算法对跟踪阶段进行多参数优化,加快了跟踪的过程;然后利用泰勒级数展开法预测发电机的转子角.该方法无需知道系统结构的先验知识,可以提前0.5 s判断各发电机的同步性,得到足够的"可用反应时间"用于在线失稳预警或就地控制.在10机39节点的新英格兰测试系统和50机145节点测试系统上的仿真结果表明了该方法的有效性.     

在线生成策略表与实时预测切机

按照策略表切机是电力系统中提高暂态稳定的有效方法之一。利用能量裕度灵敏度法在中央处理单元在线修改策略表、在故障监测单元实施实时匹配和就地预测发电机暂态稳定以决定是否切机。在厂站采用“当前”统计模型、常加速模型及常速模型构成的交互式多模型(IMM)自适应滤波算法。跟踪预测发电机转子角度。当预测到机组失稳时，按照策略表及实时匹配情况，方始发出切机命令。这种紧急切机控制的并行双重算法能有效地防止误切机组。通过经典模型下新英格兰10机39节点系统的应用说明算法的有效性。     

考虑群内运动和阻尼影响的系统模型研究

基于二群失稳模式提出了一种新的系统模型,计及了群内发电机的相对运动,并考虑了阻尼因素。假设同一机群内任意2台发电机转子角度相对该群的摆动呈线性关系,并据此对模型中的电磁功率表达式进行了化简。利用短时时域仿真数据作为输入,采用系统辨识法辨识模型参数,无需预先知道阻尼系数和机械惯性时间常数。对新英格兰10机39节点系统的仿真计算验证了该方法的准确性。该模型可应用于在线稳定预测。     

一种新型网源协调在线监测系统

针对发电机网源协调特性获取不准确,机组不能按要求出力等问题,本文提出了一种新型网源协调在线监测系统。该系统实时采集发电机的励磁、调速系统运行控制信息,并上送至调度主站。该系统能够及时捕捉系统扰动,对励磁、调速系统涉网性能进行评价,并具有预警功能。此外,该系统能够对发电机组控制系统参数进行巡检和管理。实际应用表明,该系统加强了电网与电厂对机组状态的监测,对电网安全稳定运行具有积极意义。     

DYNAMIC STABILITY OF PARALLEL CONNECTED SYNCHRONOUS GENERATORS BY THE EIGENVALUE METHOD

ABSTRACT

Parallel operation of synchronous generators is commonly used in limited independent power stations. This paper introduces an approach to the determination of dynamic stability of such electrical power stations. The role and influence of the automatic voltage regulators in improving the quality of the parallel operation is discussed. A state-space representation of a power system including two synchronous generators connected in parallel and supplying loads has been accomplished. The eigenvalues method is applied for the determination of the system dynamic stability. The method presented here has the advantage that it provides a technique for evaluating the dynamic stability limit of interconnected-synchronous generators systems. The stable loading conditions for the limited independent power station can also be found by defining the stable regions of operation. Stable-regions charts have been derived for the cases of a single generator station and a power station that consists of two parallel-connected generators. These charts are drawn for a typical independent power station supplying the electric loads of a gas plant. The comparison of the charts for a single -and two parallel generators has shown that parallel operation increases the stable regions at the same loading conditions. An induction motor load of a comparable size to that of the generating unit is applied. Its influence on the dynamic stability of the system is investigated.     

交直流混联电网发电机失步保护与直流低电压保护协调

直流输电站间通信中断情况下,当逆变侧出现故障紧急停运时,整流侧主要依靠直流低电压保护动作实现闭锁。由于整流侧通常采用定功率控制,换流器会出现低电压大电流运行并吸收大量的无功功率,若交流系统强度不够就容易造成整流侧交流母线电压大幅降低,进而引起周围发电厂内机组出现振荡直至失步。文中通过分析一起直流系统长时间低电压运行引起发电机失步保护动作的实例,指出换流站直流低电压保护应与邻近发电机失步保护相互协调,并提出了配合原则。所述原则已应用于实际直流输电工程及其邻近发电厂,显著提高了交直流混联电网运行可靠性。     

Electrical transient stability and underfrequency load sheddinganalysis for a large pump station

Electrical transients from power system faults, loss of generation and load swings can disrupt petroleum pumping station operations. Isolated stations with no utility tie, and those with weak utility ties, are especially at risk. Relative to this problem, the following four main issues are addressed: (1) analysis of the methods that use high-speed underfrequency load shedding to maintain power system stability and preserve pumping station operations; (2) analysis of combustion gas turbine generator and diesel generator transient responses, as they pertain to the electrical engineer; (3) discussion of power system component modeling and the use of low voltage circuit switching devices to shed loads; (4) and comparison of two computer analysis program outputs for underfrequency load shedding responses     

Development of frequency stabilizing scheme for integrating wind power generation into an isolated grid

Integration of wind power generation into small islands has been one of the demonstration projects in Okinawa Prefecture. Since such integration could degrade power quality including frequency in an island grid, a frequency stabilizing system using flywheels has been installed into a small island. In order to establish a proper frequency stabilizing scheme for the small island, an accurate model of a diesel generator including governor is vital. Therefore, the model was developed based on the measured values of generator dump tests. A new frequency stabilizing scheme was also developed through time‐domain simulation of the island grid model, which consists of the above‐mentioned diesel generator model and an equivalent load change representing wind power variation. The proper parameters of the scheme were derived considering role sharing between the diesel generators and the flywheels. The developed stabilizing scheme was applied to the flywheels in the island grid and revealed excellent performance in mitigating frequency variation. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(1): 24–35, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21277     

Power swing damping control by HVDC power modulation in an ac/dc hybrid transmission system

This paper describes power swing damping control by HVDC power modulation. In a hybrid system (where the ac transmission system and the HVDC system compose a loop transmission system), damping control of power swing by control of HVDC power is called power modulation control. The new HVDC link between the Shokoku and Kansai power systems forms a loop transmission system consisting of the existing ac transmission system and the new HVDC transmission system; therefore, power modulation control can be applied for stabilization of the ac system. This paper deals with a newly developed power modulation control system to damp two power-swing modes occurring in a 60-Hz interconnected system and the neighboring power system to the HVDC converter station. Characteristics of power swings in an ac systems, principles of power swing damping control by power modulation, the control system design method, and the results of verification tests by digital and analog simulators are described. It is shown that the developed power modulation system applied to the HVDC link is effective for damping two power swing modes.     

大型发电机进油原因分析及对策

发电机密封油系统的作用是为了防止外界空气进入发电机内部及阻止发电机内氢气漏出。若运行中出现发电机进油的事故。将严重危害机组的安全稳定可靠运行。为此。根据发电机密封油系统的工作原理,结合机组调试和运行中出现的事故。分析和总结了大型发电机选油的原因,并提出了具体的防范对策。     

灯泡贯流式水轮发电机组的局放在线监测

针对水轮发电机组结构及汇流母线排走线方式的特点,选择发电机每相高压出线处为系统监测点,利用双安装传感器定向耦合实现干扰脉冲抑制。该系统分别在电站6台发电机主引出线上安装近、远端两路传感器(6只/每台机组),耦合放电信号,经过信号的选通、滤波处理后进入监测系统,利用软件进行时延幅值判别,提取放电信号,并进行二维、三维谱图分析。对比分析了现场测到的放电信号与干扰信号在时域及幅值上的差别,验证了抗干扰方法的有效性。自第一台机组并网发电以来,系统运行稳定、操作方便,所测结果与预试数据基本一致。