GB/T 7409.22020 PDF in English
GB/T 7409.22020 (GB/T7409.22020, GBT 7409.22020, GBT7409.22020)
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Excitation systems for synchronous machinesPart 2: Models for power system studies
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Standards related to: GB/T 7409.22020
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GB/T 7409.22020: PDF in English (GBT 7409.22020) GB/T 7409.22020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 29.160.20
K 21
Replacing GB/T 7409.22008
Excitation Systems for Synchronous Machines  Part 2:
Models for Power System Studies
ISSUED ON: JUNE 2, 2020
IMPLEMENTED ON: DECEMBER 1, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 4
Introduction ... 6
1 Scope ... 8
2 Normative References ... 8
3 Terms and Definitions ... 8
4 Classification of Exciters  Graphical Method and Mathematical Model for Stability
Studies ... 9
4.1 DC Exciters ... 9
4.2 AC Exciters ... 10
4.3 Potential Source Static Exciter ... 15
4.4 Compound Source Static Exciter ... 16
5 Mathematical Models of Control Functions ... 17
5.1 Voltage Measurement and Load Current Compensation Link Model ... 17
5.2 Proportionalintegralderivative (PID) Correction Link Model ... 19
5.3 Excitation Feedback Link Model ... 20
5.4 Amplitude Limiting Link ... 21
5.5 Power System Stabilizer Model ... 21
5.6 General Structure of Main Voltage Control ... 22
5.7 Auxiliary Limiter Model ... 23
5.8 Mode of Auxiliary Limiter’s Intervention in Main Voltage Control ... 27
6 Excitation System Models ... 28
6.1 Overview ... 28
6.2 Excitation System Models for AC Exciters ... 28
6.3 Excitation System Models for DC Exciters ... 31
6.4 Static Excitation System Model ... 31
7 Terminology ... 33
7.1 Parameters ... 33
7.2 Variables ... 36
Appendix A (informative) Transformer Highvoltage Side Voltage Control Model ... 39
Appendix B (normative) Amplitude Limiting Expression Method ... 40
Appendix C (informative) Multiband Power System Stabilizer Model ... 44
Appendix D (normative) Inverse Time Characteristic Calculation ... 46
Appendix E (informative) UEL Model Table Lookup Function... 48
Appendix F (informative) Integral Reset Representation ... 49
Appendix G (normative) Saturation Function ... 50
Appendix H (normative) Rectifier Regulation Characteristics ... 51
Appendix I (informative) Estimation of Over Excitation Limiter (OEL) Reference
Value ... 53
Appendix J (normative) Perunit System ... 60
Bibliography ... 61
Excitation Systems for Synchronous Machines  Part 2:
Models for Power System Studies
1 Scope
This Part of GB/T 7409 specifies the simulation diagram of the excitation system, the
mathematical model of the exciter and control functions, and the terminology definitions of its
related parameters and variables.
This Part is applicable to the excitation system models of steam (gas) turbine generators,
hydroelectric generators, pumped storage power generators / motors and nuclear power units
used in the power system studies and analysis.
2 Normative References
The following documents are indispensable to the application of this document. In terms of
references with a specified date, only versions with a specified date are applicable to this
document. In terms of references without a specified date, the latest version (including all the
modifications) is applicable to this document.
GB/T 7409.1 Excitation Systems for Synchronous Electrical Machines  Definitions
3 Terms and Definitions
The terms and definitions defined in GB/T 7409.1, and the following are applicable to this
document.
3.1 main voltage control
The link of comparing the actual measured value of the synchronous generator terminal voltage
with the given value and adjusting the excitation output with appropriate control rules in
accordance with its deviation.
NOTE: its main functions also include load current compensation, excitation feedback link and
power system stabilizer (PSS) functions.
3.2 auxiliary limiters
The limiting link in the excitation regulator other than the main voltage control.
NOTE: it includes V/Hz limiter, over excitation limiter, maximum current limiter, stator current
limiter and under excitation limiter, etc.
3.3 maximum current limiter
Under any operating conditions, the output current of the excitation system is instantaneously
limited to not exceed the specified maximum value.
3.4 volts per hertz limiter; VEL
An additional unit or function in a voltage regulator that prevents the voltagetofrequency ratio
of a synchronous machine or its connected transformer from exceeding an allowable range.
3.5 over excitation limiter; OEL
An additional unit or function in a voltage regulator that limits the output current of the
excitation system to an allowable value.
3.6 stator current limiter; SCL
An additional unit or function in a voltage regulator that limits the stator current within an
allowable value by adjusting the reactive component of the stator current of the synchronous
generator during over excitation or under excitation.
3.7 under excitation limiter; UEL
An additional unit or function in a voltage regulator that limits the reactive power of the
synchronous generator to no less than a specified value under different active loads.
4 Classification of Exciters  Graphical Method and
Mathematical Model for Stability Studies
4.1 DC Exciters
In recent years, although DC exciters have been rarely used in new units, some synchronous
machines are still equipped with such exciters. Figure 2 is a schematic diagram of an DC exciter
using separately excited windings, and Figure 3 demonstrates the model of the exciter. In the
model, the constant KE of the selfexcited magnetic field of the AC and DC exciters is used to
describe the characteristics of the exciter with selfexcited components. Please be noted that
when adopting the separately excited exciters, KE = 1.
XErectifier load factor, which is proportional to the commutation reactance of the voltage
source and current source, or the combined equivalent commutation reactance of the voltage
and current source, see Appendix H.
Fecommutation pressure drop coefficient, see Appendix H.
Xcommutation reactance.
KIcurrent loop input constant.
KPvoltage loop input constant.
Uf max, Uf minmaximum and minimum voltage output by the excitation system.
Ur max, Ur minmaximum and minimum output of the regulator
UFE maxexciter magnetic field current limiting parameter.
UP+, UPat the rated voltage of the generator, the maximum and minimum noload output
voltage of the potential source exciter.
KGfeedback gain of the inner loop magnetic field regulator.
KRgain of voltage measurement link.
KZstatic difference compensation coefficient of the control link, which is generally set to the
reciprocal of the proportional gain KS of the control link.
TRtime constant of terminal voltage converter and load current compensator.
XPrectifier load factor of potential source converter, see Appendix H.
KMAXproportional gain constant coefficient, which is generally set to 1,000,000.
KA, KA1, KFF, KV, KAP, KAD, KAI, KB, KBP, KBIvoltage regulator gain constant.
KF, KHgain constant of excitation feedback link.
TB1, TB2, TC1, TC2, TA, TB, TAD, TGvoltage regulator time constant.
TFtime constant of excitation feedback link.
XC, RCcurrent and power compensator gain constants.
UA max, UA min, UA1 max, UA1 min, UA2 max, UA2 min, UB max, UB min, UD max, UD min, UI max, UI minvoltage
regulator amplitude limiting values.
KL1over excitation instantaneous limit gain.
UL1Rover excitation instantaneous setting value.
KPSS, KS1, KS2, KS3power system stabilizer gain.
TS1, TS2time constant of power system stabilizer signal measurement link.
TW1, TW2, TW3, TW4time constant of DC blocking link of power system stabilizer.
TP1, TP2, TP3, TP4, TP5, TP6, TP7, TP10, TP11power system stabilizer time constant.
A1, A2, M, N, TP8, TP9power system stabilizer filter parameters.
USS max, USS minpower system stabilizer output amplitude limiting values.
USI1 max, USI1 min, USI2 max, USI2 minpower system stabilizer input amplitude limiting values.
UfB, IfB, RfB UefB, IefB, RefBrespectively: generator magnetic field voltage, field current and
field winding resistance reference value, exciter field voltage, field current and field winding
resistance reference value.
UVF_REFfixed value amplitude limiting value (expressed by the perunit value of the rated
value).
Kinv, Kcoolheat accumulation and heat dissipation integral coefficient.
KexpVELinverse time characteristic exponential coefficient of V/Hz limiter.
UVFL_thinverse time timing start setting value of V/Hz limiter (expressed by the perunit value
of the rated value).
UVFL_rthaction return fixed value of V/Hz limiter (expressed by the perunit value of the rated
value).
UREF maxoutput maximum setting value of V/Hz limiter (expressed by the perunit value of
the rated value).
KexpOELinverse time characteristic exponential coefficient of OEL limiter.
Ifthinverse time limit timing start setting value of OEL limiter (expressed by the perunit value
of the rated value, and the setting value setting can be found in Appendix I).
Ifnheat accumulation rotor current reference value of OEL limiter (expressed by the perunit
value of the rated value, and the setting value setting can be found in Appendix I).
Ifrthinverse time limit setting value of OEL (expressed by the perunit value of the rated value,
and the setting value setting can be found in Appendix I).
If maxmaximum magnetic field current setting value allowed by OEL (expressed by the per
unit value of the rated value, and the setting value setting can be found in Appendix I).
Cupper amplitude limiting value of heat accumulation integral.
P, Qactive power and reactive power of the generator (expressed by the perunit value of the
apparent rated value).
IP, IQactive current and reactive current of the generator (expressed by the perunit value of
the apparent rated value).
generator power angle.
Ueexciter voltage after commutation reactance (expressed by the perunit value of the
generator air gap magnetic field voltage).
UREFvoltage regulator setting value (determined in accordance with the initial conditions).
Upssoutput of power system stabilizer.
Upss1, Upss2, Upss3outputs of the power system stabilizer intervening in the main voltage control
at different positions.
UERRdeviation signal of the voltage control channel.
Uessoutput of excitation feedback link.
Uiea signal proportional to the exciter magnetic field current.
UCvoltage measurement and compensator output.
UAoutput of voltage correction link.
USI1, USI2input signals of power system stabilizer.
fGgenerator frequency (expressed by the perunit value of power frequency 50 Hz).
UVF_REFfixed value output of V/Hz limiter.
UVFLoutput of V/Hz limiter.
UVFL1, UVFL2, UVFL3outputs of V/Hz limiter intervening in the main voltage control at different
positions.
SOELOEL action flag bit (expressed by 0 and 1).
UOELinverse time limit output of OEL limiter.
UOEL1, UOEL2, UOEL3, UOEL4, UOEL5outputs of OEL limiter intervening in the main voltage
control at different positions.
USCL1, USCL2outputs of SCL limiter adopting the superposition mode to intervene in the main
voltage control at different positions.
USCLind, USCLcapSCL delayed phase side limit output and advanced phase side limit output.
Appendix J
(normative)
Perunit System
In power system studies, the voltage and current of the generator and exciter, as well as the
input and output quantities of the regulator are expressed by perunit values. The perunit
system shall be established in accordance with the following requirements:
a) The perunit value is equal to the actual value divided by the reference value.
b) The reference value of the generator voltage is the generator rated voltage. The
reference value of the generator current is the generator rated current. The reference
value of the generator power is the rated apparent power of the generator. The
reference value of the generator frequency is the generator rated frequency.
c) The reference value IfB of the generator magnetic field current is the magnetic field
current required to generate the rated voltage on the generator’s noload characteristic
air gap curve. The reference value RfB of the generator magnetic field winding
resistance is the generator’s rated magnetic field voltage divided by the generator’s
rated magnetic field current. Under certain circumstances, the influence of the loop
resistance needs to be considered. The reference value UfB of the generator magnetic
field voltage is the reference value of the magnetic field current multiplied by the
reference value of the magnetic field winding resistance.
d) The reference values of the output current and voltage of the exciter are respectively
the reference values of the generator magnetic field current and voltage.
e) The reference value IefB of the exciter magnetic field current is the exciter magnetic
field current value required to generate a perunit value of generator magnetic field
voltage on the air gap curve of the exciter noload characteristic curve. The reference
value RefB of the exciter magnetic field winding resistance is the resistance of the
excitation circuit of the exciter under the rated operating conditions of the generator.
The reference value UefB of the exciter magnetic field voltage is the reference value
of the exciter magnetic field current multiplied by the reference value of the exciter
magnetic field winding resistance.
f) The reference values of the input voltage, current and power of the regulator are equal
to the reference values of the generator voltage, current and power. When controlling
the generator magnetic field voltage, the reference value of the regulator output
voltage is equal to the reference value of the generator magnetic field voltage. When
controlling the exciter magnetic field voltage, the reference value of the regulator
output voltage is equal to the reference value of the exciter magnetic field voltage.
...... Source: Above contents are excerpted from the PDF  translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
