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GB/T 7409 consists of the following three parts under the general title Excitation systems for synchronous machines:
——GB/T 7409.1 Excitation systems for synchronous electrical machines — Definitions;
——GB/T 7409.2 Excitation systems for synchronous machines — Part 2: Models for power system studies;
——GB/T 7409.3 Excitation system for synchronous electrical machines — Technical requirements of excitation system for large and medium synchronous generators.
This part is Part 2 of GB/T 7409.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 7409.2-2008 Excitation systems for synchronous machines — Models for power system studies, and the following main technical changes have been made with respect to GB/T 7409.2-2008:
——"Detailed description of auxiliary limiter model of excitation system" has been added, and the established model of generator excitation system can provide a simulation comparison between main generator excitation systems in China and field measured data, and can be used for analysis of power system stability (see 5.7);
——The load current compensation model based on scalar superposition has been added (see 5.1);
——Some voltage correction models and their description have been modified (see 5.3; 3.5.2 of Edition 2008);
——Some power system stabilizer models have been added (see 5.5);
——VFL, OEL, SCL and UEL models have been added (see 5.7);
——The interference ways of various auxiliary limiters and the power system stabilizer in the main voltage control have been added (see 5.8);
——"Voltage control model of transformer high-voltage side" has been added (see Annex A);
——“Multi-band power system stabilizer model” has been added (see Annex C);
——“Calculation equation of inverse time characteristic” has been added (see Annex D);
——The content of the former Annex E and F has been deleted (see Annexes E and F of Edition 2008);
——"Look-up table function for UEL model" (see Annex E);
——"Integral reset representation" has been added (see Annex F);
——"Method for estimating field current” has been added and this method may be used for setting OEL characteristics (see Annex I);
This part was proposed by the China Electrical Equipment Industry Association.
This standard is under the jurisdiction of the National Technical Committee on Electric Rotating Machinery of Standardization Administration of China (SAC/TC 26).
The previous editions of this part are as follows:
——GB 7409-1987;
——GB/T 7409.2-1997 and GB/T 7409.2-2008.
Introduction
In the study of power system stability, as the operating state of synchronous machine has been accurately simulated, an appropriate model shall be established for the excitation system of the machine. Due to the limitation of data acquisition, programming and calculation, it is necessary to use a simplified model with appropriate accuracy if permitted. These models shall be suitable for showing the performance of excitation system in the following periods:
——the period of steady-state conditions before a fault occurs;
——the period from fault occurrence to fault clearance;
——the period of oscillation after fault clearance.
Assuming that the frequency deviation is within ±5% of the rated value in the steady-state study, the influence of frequency deviation on excitation model may be ignored.
The excitation system model shall be effective for steady-state conditions and natural oscillation frequency of synchronous machine. Generally, the typical value of this oscillation frequency is not larger than 3 Hz.
The functions of protection and actions of de-excitation and overvoltage suppressor are not included in the application scope of the models. More detailed models shall be considered in the study of out-of-step operation, subsynchronous resonance/oscillation or torsional vibration of shafting.
The excitation modeling method and standard model may also be used for other dynamic problems related to synchronous machine, but it is necessary to check the applicability of the models for this study.
In the study of power system, the functions of various excitation systems involved are given in the block diagram of Figure 1. These functions include:
——voltage control element;
——auxiliary limiter;
——power system stabilizer;
——excitation feedback;
——exciter.
The main distinguishing feature of exciter is the way of providing and transforming excitation power.
This part proposes a general and practical calculation model of generator excitation system, which can meet the requirements of power system stability analysis, with reference to the actual model of generator excitation system in China and the calculation model of generator excitation system for power system stability analysis, and the standard IEEE Std.421.5-2016,
Figure 1 General functional block diagram of synchronous machine excitation system
(part in dashed box)
Excitation systems for synchronous machines — Part 2: Models for power system studies
1 Scope
GB/T 7409.2 stipulates the simulation diagram of excitation system, the mathematical model of exciter and control function, and the terms and definitions of related parameters and variables.
GB/T 7409.2 is applicable to the excitation system models of steam (gas) turbine generators, hydro-generators, pumped storage generators/motors and nuclear power units used in power system research and analysis.
2 Normative references
The following referenced document is indispensable for the application of this standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced documents (including any amendments) applies.
GB/T 7409.1 Excitation systems for synchronous electrical machines — Definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 7409.1 and the following apply.
3.1
main voltage control
link in which the actual measured value of the terminal voltage of synchronous generator is compared with the given value, and the excitation output is adjusted based on its deviation and appropriate control law
Note: Its main functions also include load current compensation, excitation feedback and power system stabilizer (PSS).
3.2
auxiliary limiters
limiters in excitation regulator except main voltage control
Note: limiters include volts per hertz limiter, over excitation limiter, maximum current limiter, stator current limiter, under excitation limiter, etc.
3.3
maximum current limiter
transient limiter for output current of the excitation system not to exceed the specified maximum in any operating conditions
3.4
volts per hertz limiter; VFL
additional unit or function of voltage regulator to avoid a higher ratio of voltage to frequency of synchronous motor or a higher ratio of voltage to frequency of the transformer connected to the motor than the allowable range
3.5
over excitation limiter; OEL
additional unit or function of voltage regulator that limits the output current of excitation system within the allowable value
3.6
stator current limiter; SCL
additional unit or function of voltage regulator that limits the stator current within the allowable value by adjusting the reactive component of the stator current of synchronous generator in over excitation or under excitation
3.7
under excitation limiter; UEL
additional unit or function of voltage regulator that limits the reactive power of synchronous generator to be not lower than the specified value under different active loads
4 Classification of exciter——graphic method and mathematical model for stability study
4.1 DC exciter
In recent years, although DC exciter is rarely used in new units, there remain some synchronous motors equipped with such exciters. Figure 2 is a schematic diagram of DC exciter using separately excited windings, and Figure 3 shows the model of this exciter. In the model, the constant KE of self-excited magnetic field of AC and DC exciter is used to describe the characteristics of exciter with self-excited component. Note: KE=1 when using separated exciter.
Foreword i Introduction iii 1 Scope 2 Normative references 3 Terms and definitions 4 Classification of exciter——graphic method and mathematical model for stability study 4.1 DC exciter 4.2 AC exciter 4.3 Potential source static exciter 4.4 Compound source static exciter 5 Mathematical model of control function 5.1 Model of voltage measurement and load current compensation 5.2 Proportional-Integral-Differential (PID) correction model 5.3 Excitation feedback model 5.4 Limit 5.5 Power system stabilizer model 5.6 General structure of main voltage control 5.7 Model of auxiliary limiter 5.8 The mode of the auxiliary limiters intervening in the main voltage control 6 Model of excitation system 6.1 General 6.2 Model of AC exciter excitation system 6.3 Model of DC exciter excitation system 6.4 Static excitation system model 7 Symbols 7.1 Parameters 7.2 Variables Annex A (Informative) Voltage control model of transformer high-voltage side Annex B (Normative) Expression of limit Annex C (Informative) Multi-band power system stabilizer model Annex D (Normative) Calculation equation of inverse time characteristic Annex E (Informative) Look-up table function for UEL model Annex F (Informative) Integral reset representation Annex G (Normative) Saturation function Annex H (Normative) Rectifier setting characteristics Annex I (Informative) Estimation of baseline value of over excitation limiter (OEL) Annex J (Normative) Per unit system Bibliography
同步电机励磁系统 第2部分：电力系统研究用模型 1 范围 GB/T 7409的本部分规定了励磁系统模拟简图、励磁功率单元和控制功能的数学模型，及其相关参数和变量的术语定义。 本部分适用于电力系统研究和分析中所使用的汽(燃气)轮发电机、水轮发电机、抽水蓄能发电/电动机和核电机组的励磁系统模型。 2 规范性引用文件 下列文件对于本文件的应用是必不可少的。凡是注日期的引用文件，仅注日期的版本适用于本文件。凡是不注日期的引用文件，其最新版本(包括所有的修改单)适用于本文件。 GB/T 7409.1 同步电机励磁系统 定义 3 术语和定义 GB/T 7409.1界定的以及下列术语和定义适用于本文件。 3.1 电压控制主环 main voltage control 将同步发电机机端电压的实际测量值与给定值进行比较，并按其偏差以适当的控制规律调节励磁输出的环节。 注：其主要功能中还包含负载电流补偿、励磁反馈环节及电力系统稳定器( power system stabilizer， PSS)功能。 3.2 辅助限制环节 auxiliary limiters 励磁调节器中除电压控制主环以外的限制环节。 注：其包含V/Hz限制、过励限制、最大励磁电流限制、定子电流限制、欠励限制等。 3.3 最大励磁电流限制 maximum current limiter 任何运行工况下，瞬时限制励磁系统输出电流不超过规定的最大值。 3.4 V/Hz限制 volts per hertz limiter； VFL 电压调节器中一种防止同步电机或与其相连变压器的电压与频率之比超过允许范围的附加单元或功能。 3.5 过励限制 over excitation limiter； OEL 电压调节器中一种将励磁系统输出电流限制在允许值之内的附加单元或功能。 3.6 定子电流限制 stator current limiter； SCL 电压调节器中一种在过励或欠励时通过调整同步发电机定子电流的无功分量来限制定子电流在允许值之内的附加单元或功能。 3.7 欠励限制 under excitation limiter； UEL 电压调节器中一种在不同有功负荷下限制同步发电机无功功率不低于规定值的附加单元或功能。 4 励磁功率单元分类——图示法及稳定性研究的数学模型 4.1 直流励磁机励磁功率单元 近年来，虽然新机组已很少采用直流励磁机，但还有部分同步电机装有这类励磁机。图2就是一种采用它励绕组的直流励磁机励磁功率单元简图，图3表示该励磁功率单元的模型。模型中用交、直流励磁机自励磁场的常数KE来描述有自励分量励磁机的特性。注意：采用它励励磁机时KE＝1。
图22 单输入信号电力系统稳定器模型——PSS1型 b) 合成加速功率型电力系统稳定器模型——PSS2型 PSS2型合成加速功率型电力系统稳定器模型见图23。PSS2型模型采用发电机转速(或频率)和有功功率作为输入信号USI1和USI2，经过运算产生机械功率变化量信号，该信号减去有功功率变化量信号即为加速功率变化量信号，以此作为电力系统稳定器校正信号输入到超前滞后环节、增益调整环节和限幅环节。
图23 加速功率型电力系统稳定器模型——PSS2型 c) 其他电力系统稳定器模型，比如多频段PSS模型(参见附录C)。 5.6 电压控制主环通用结构 电压控制主环通常由几种校正环节组合而成，其通用结构模型见图24，图中虚线描述了励磁反馈环节和电力系统稳定器可选择的介入位置。励磁系统稳定计算模型可按照实际模型或按照等效方式设置KA、KB、TA、TB、KFF和PID1、PID2对应的参数，选择励磁反馈环节和电力系统稳定器介入点。KH设置为0时励磁反馈校正环节为软反馈校正，KF、TF设置为零时该环节为励磁机时间常数补偿环节。
