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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.
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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.
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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
