Underexcitation limiter models for power system stability studies

Underexcitation limiter models suitable for use in large scale power system stability studies are presented. These models are compatible with recommended excitation system models. Using these models, it is expected that most underexcitation limiters in use on large power system-connected synchronous machines can be represented     

Recommended models for overexcitation limiting devices

Overexcitation, overvoltage, and overfluxing limiter models suitable for use in large scale power system stability studies are presented. These models are compatible with current IEEE recommended excitation system models. With these models, most of the limiters of these types in use on large, power system-connected synchronous machines in North America can be represented     

Development of a Small-Scale Generator Set Model for Local Network Voltage and Frequency Stability Analysis

The integration of numerous small-scale generators into existing local networks (e.g., a microgrid) is anticipated to impact their operation, control, and protection. In particular, maintaining voltage and frequency stability within the defined limits is more onerous and requires investigation. The effect of protective limiters and characteristics such as the genuine inertia of the generation set must be taken into consideration in stability studies in order to accurately represent the overall dynamic characteristics of local distributed generators. This paper focuses on three fundamental aspects: 1) the development of a reciprocating engine/generator set model; 2) the laboratory testing of an experimental test rig; and 3) the influence of a volts-per-hertz ratio (volts-per-hertz ratio) limiter on the generator dynamic response. The experimental procedures used to determine the genuine inertia of the test rig are described and the system responses under different scenarios are used to validate the developed model. This emphasizes the significance of excitation protective limiters such as volts-per-hertz ratio, during the stability analysis.     

Computer models for representation of digital-based excitationsystems

Computer models suitable for representation of newer digital-based excitation systems in transient stability programs are presented in this paper. These models are an addendum to the most recent issued IEEE standard 421.5 (1992) for recommended excitation system models. It is the intent of the subcommittee to include these models in standard 421.5 at the time of its next revision. This paper covers, static excitation systems and alternator supplied rectifier excitation sytems     

Verification of limiter performance in modern excitation controlsystems

Modern excitation systems include devices for controlling or limiting machine terminal voltage (overvoltage limiters), volts per hertz ratio (V/Hz limiters), maximum machine field current (overexcitation limiters), and the reactive load absorbed by the machine (underexcitation limiters). Functional testing of these limiters before they are placed into commercial service is recommended. The Bureau of Reclamation (USA) routinely performs functional testing to determine the actual settings and operational characteristic of these limiters as part of excitation system commissioning tests on its hydroelectric generators. This paper discusses the purpose and practice of functionally testing these limiters     

Minimum/maximum excitation limiter performance goals for smallgeneration

Small generators connected to the electric utility system often act as followers as they tend to follow power system bus voltage variations. For the lack of kVA capacity, small machines tend to be susceptible to becoming over or underexcited (excessive VArs in or VArs out of the generator) as the voltage regulator tries to maintain its setpoint with variations in system bus voltage. Minimum and maximum excitation limiters are utilized to limit the voltage regulator characteristic response to system bus voltage changes, that can otherwise result in machine overheating and/or pulling out of synchronization. This paper reviews the operating performance of minimum and maximum excitation limiters used on small machines, and provide the user typical performance expectations. The examples shown by the authors highlight both main field and exciter field applications     

Minimum excitation limiter effects on generator response to systemdisturbances

Minimum excitation limiters (MEL) have been in use since the first applications of voltage regulators to synchronous machines, and are presently in widespread use throughout the power industry. However, a cursory literature search indicates scant examination of the dynamic behavior of these devices. Although the minimum excitation limiter is rarely called into action, its effect can be particularly significant to the final outcome of some severe disturbances. The digital computer modeling of two common MEL devices is described, and their effect on power system dynamics is addressed     

Design of Volts per Hertz limiter with consideration of theunder-excitation limiter control actions

The dynamical relationship between the Volts per Hertz limiter and the under-excitation limiter control loops in a synchronous generator is examined using the frequency response technique. From the analysis, it is concluded that sustained oscillations due to the interaction between the two limiters can occur should the loading level of the generator exceeds a certain threshold value. For generator operation below this value, a systematic design procedure has been proposed for the limiters which will ensure network stability     

Wide-area fuzzy logic control of voltage/VAr under simulated onlineconditions

This work describes the development of a fuzzy logic tool capable of controlling system voltages and VAr resources, as well as processing alarms related to voltage stability. The fuzzy controller monitors voltages and VAr resources and generates appropriate control signals to each VAr source to maintain acceptable system voltage levels. The fuzzy alarm processor generates an individual alarm for each voltage region, and a general alarm signal that indicates the overall system condition. A prototype fuzzy controller/processor has been interfaced with power system simulation software to test its performance under simulated on-line conditions     

基于BPA的励磁系统建模

励磁系统在源网协调运行中正发挥着越来越重要的作用,建立准确可靠的励磁系统模型是研究电网稳定性的基础,是稳定性结论真实可靠的必要保证,是制定合理的电网运行策略的重要条件。为了在BPA中研究发电机的稳定性,通过空载试验等现场实测的方法,获取发电机励磁系统的动态特性和模型特征。在励磁系统数学模型的基础上,通过建模仿真以及参数辨识的方法,建立了BPA可以调用的励磁系统模型,整定模型参数。通过BPA搭建了单机无穷大仿真模型,验证了模型的正确性。验证结果表明：整定模型与实际励磁系统具有相同的动态特性,为电力系统稳定性研究工作提供了真实可信的模型。     

共轨柴油机燃油限压阀设计研究

锥面密封式和钢球密封式两种共轨柴油机燃油限压阀结构基本原理相同。共轨燃油限压阀设计的基本方法是根据共轨管最大允许油压和喷油泵单位时间供给共轨管的最大油量,来确定限压阀节流小孔直径、弹簧刚度等结构参数的值。并用已成熟的BOSCH公司产品进行了验算。     

A utility perspective on under-excitation limiters

This paper presents a brief review of Ontario Hydro's perspective and experience with power system under excitation limiters (UELs). The purpose of the UEL is reviewed along with the results of field testing and modelling. It is concluded that users of these devices must define the dynamic performance requirements of the limiters, by examining the purpose of their installation, and then setting and testing them accordingly     

Application of magnetic energy storage unit as continuous VArcontroller

It is shown that magnetic energy storage units can simultaneously operate as continuous VAr (volt-ampere reactive) controllers while performing the role of load-frequency stabilizers in electrical power systems. This is achieved by operating the converter in the buck-boost mode with a switched capacitor bank placed across its terminals. The P versus Q modulation ranges of the 12-pulse converter depend on the source inductance, secondary voltage of the input transformers, and output current. Once the input transformer is chosen, the Q modulation range depends on the active power transfer and the current through the inductor at any instant of time. The actual reactive power consumption of the converter is varied continuously, depending on the requirements of the power system, while keeping within the Q-modulation range. Switching of the capacitor bank keeps the required Q consumption of the converter within the available range. It is shown that this mode of control improves the overall performance of the power system in P-f and Q-V loops and obviates the use of any additional VAr compensator in the power area where the SMES (superconducting magnetic energy storage) unit is located     

Developing multiple regression models from the manufacturer's ground-source heat pump catalogue data

The performance of ground-source heat pumps (GSHP), often expressed as Power drawn and/or the COP, depends on several operating parameters. Manufacturers usually publish such data in tables for certain discrete values of the operating fluid temperatures and flow rates conditions. In actual applications, such as in dynamic simulations of heat pump system integrated to buildings, there is a need to determine equipment performance under operating conditions other than those listed. This paper describes a simplified methodology for predicting the performance of GSHPs using multiple regression (MR) models as applicable to manufacturer data. We find that fitting second-order MR models with eight statistically significant x-variables from 36 observations appropriately selected in the manufacturer catalogue can predict the system global behavior with good accuracy. For the three studied GSHPs, the external prediction error of the MR models identified following the methodology are 0.2%, 0.9% and 1% for heating capacity (HC) predictions and 2.6%, 4.9% and 3.2% for COP predictions. No correlation is found between residuals and the response, thus validating the models. The operational approach appears to be a reliable tool to be integrated in dynamic simulation codes, as the method is applicable to any GSHP catalogue data.     

Analysis of grid connected induction generators driven byhydro/wind turbines under realistic system constraints

Results of an investigation dealing with the behaviour of grid-connected induction generators (GCIGs) driven by typical prime movers such as mini-hydro/wind turbines are presented. Certain practical operational problems of such systems are identified. Analytical techniques are developed to study the behavior of such systems. The system consists of the induction generator (IG) feeding a 11 kV grid through a step-up transformer and a transmission line. Terminal capacitors to compensate for the lagging VAr are included in the study. Computer simulation was carried out to predict the system performance at the given input power from the turbine. Effects of variations in grid voltage, frequency, input power, and terminal capacitance on the machine and system performance are studied. An analysis of self-excitation conditions on disconnection of supply was carried out. The behavior of a 220 kW hydel system and 55/11 kW and 22 kW wind driven system corresponding to actual field conditions is discussed     

UNITROL5000励磁系统原理及典型故障分析

ABB公司研发的UNITROL 5000型数字式励磁系统被采用在景德镇发电厂的2台660 MW发电机组中,被发电厂作为最重要的电气设备而被加以研究和维护。简要介绍该型励磁系统组成原理及设备结构,并分析了几个励磁系统中出现的重大缺陷和故障案例,为提高今后发电厂励磁系统安全性及稳定性提供了有益的经验。     

How lifetime fluctuations, grain-boundary recombination, and junctions affect lifetime measurements and their correlation to silicon solar cell performance

Two-dimensional simulations of quasi-steady-state photoconductance (QSSPC), carrier density imaging (CDI), photoconductive decay (PCD), and solar cell performance are performed on silicon models that incorporate grain-boundary recombination or lifetime fluctuations on the distance scale of 5 μm to 5 mm. The relationships between the lifetime measurement, actual recombination rates, and solar cell performance vary widely based on beam size, measurement technique, and recombination profile. The strengths and weaknesses of different measurement methods and the ability of analytical models to predict aggregate solar cell performance are examined and compared with earlier studies. Lifetime measurements in the presence of a junction are shown to be distorted by charge separation.     

A self-tuning automatic voltage regulator designed for anindustrial environment

Examination of the performance of fixed parameter controllers has resulted in the development of self-tuning strategies for excitation control of turbogenerator systems. In conjunction with the advanced control algorithms, sophisticated measurement techniques have previously been adopted on micromachine systems to provide generator terminal quantities. In power stations, however, a minimalist hardware arrangement would be selected leading to relatively simple measurement techniques. The performance of a range of self-tuning schemes is investigated on an industrial test-bed, employing a typical industrial hardware measurement system. Individual controllers are implemented on a standard digital automatic voltage regulator (AVR), as installed in power stations. This employs a VME platform, and the self-tuning algorithms are introduced by linking to a transputer network. The AVR includes all normal features, such as field forcing, VAr limiting and overflux protection. Self-tuning controller performance is compared with that of a fined gain digital AVR     

Multivariable adaptive control for a thermal generator

A digital control system using the optimal control has been developed for a thermal power generator. In order to increase the generator control performance for improving the power system stability, this system supplies the excitation system directly with control signals and provides the governor system with control signals and supplemental control signals for a conventional governor. The system utilizes adaptive control for changes in generator nonlinear characteristics, as well as in power system characteristics. The principles and application of this system are described and results of simulation tests using a 1000 MVA thermal power plant model on a high-reliability AC/DC electric power system simulator are presented. The results verify the performance of this system, as well as the applicability of the system to actual plants     

一种经济型故障限流器及其控制策略

提出了一种应用柔性输电技术改善电网电能质量和提高稳定性的经济型短路故障限流器。在输电线路正常运行时,串联在线路中,几乎无能量损耗;当有故障发生时,快速切换到故障限流模式,有效的限制短路电流。分析了这种经济限流器的参数整定及其控制策略,并利用PSCAD和MATLAB软件对其进行了特性分析和电磁暂态稳定性仿真,结果证明了该模型有良好的限流性能和控制策略的可行性。