ppt on dyn simulation.pdf
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Power system analyses(Dynamic modeling)
Using PSS/E for power system analyses- Excitation system modeling -
Istanbul, May 2011
IntroductionIt is important to model excitation system of a generator due to the crucial influence to the transient processes in a power plant during the disturbance (first 10 seconds)Largest influence is present in:
maintaining steady voltage setpoint of generator terminalelectromagnetic processes of synchronous machine, capability of machine to dampen the small signal oscillations (small signal stability)
Least influence is present in Active Power-Frequency loop (Pf control)
Principle scheme of excitation
Rotating excitation systems
Non rotating excitation systems
Main Objectives
To identify the types of excitation systems in Black Sea Region
To collect as much data as possible for these excitation systems
Select the proper model from PSS/E dynamic library
DC excitation systems
DC excitation system
It uses DC machines (with parallel or independent self excitation) for electromechanical amplification of control signals and generation of field current for rotor circuit of synchronous generatorSpecial DC machines (amplidynes) are commonUsed widely during 50’s and 60’s and now considered as obsolete
DC excitation system
Advantages:Independency toward the voltage occurrences in grid in some cases
Backdraws:Decreased reliability due to the usage of many partsSlow response during the transient processesLow amplification of control signals inside the excitation system
DC excitation system
There are several models for DC excitation systems in PSS/E library:
generic models: IEEET1, IEEEX1, IEEEX4, IEEET5
more detailed models: ESDC1A, ESDC2A, EXDC2, IEET1B, IEEET4 , IEEET5A, DC4B
DC excitation system
Recommendation is to use IEEET1 and ESDC1A as a representation in PSS/E is with (it is the simplest one and it covers all the necessary parts)
DC excitation system
Parameter ranges for various DC excitation systems
KA usually less than
150
AC excitation systems
AC excitation systems
It uses AC machine to generate AC excitation voltage which is then rectified over a diode or thyristor bridgeRotor of synchronous generator may have slide contact rings or it could be brushlessVarious types of controllers for regulator could be used (PI, PID, Fuzzy, Neural etc.)In case of brushless excitation system, special type of excitation generator is usedWidely used excitation system
Advantages:Independency toward the voltage occurrences in grid in some casesExpanded range for excitation voltages and currents with high amplificationVery fast response
Backdraws:Decreased reliability due to the usage of many partsCommutation drop in brushless systemsDependency toward the voltage occurrences in grid in some cases
AC excitation systems
AC excitation systems
There are several models for AC excitation systems in PSS/E library:
alternators with non controlled rectifiers: EXAC1/2/3, ESAC1/2/3A, EXAC1A, ESAC5A, ESAC6A, ESAC8B, EXPIC, AC7B, AC8B
alternators with thyristor bridges: EXAC4, ESAC4A, EX2000, EXBAS
AC excitation systems
Fundamental difference between “western”and “eastern” control logic
GVoltage controller
Excitation limiters
Power system
stabilizer
V, deltaV
P, f, dV/dt, df/dt
V, deltaV, Pel, Qel
GVoltage
controller
V, deltaV
Ifd, dV/dt, df/dt, (d2V/dt2)
Pel, Qel, f, I
Σ
AC excitation systems
Recommendation is to use EXAC4 or ESAC4A as a representation in PSS/E (but not alone)
AC excitation systems
In case of brushless excitation, recommendation is to use EXAC1 or ESAC1A as a representation in PSS/E (but not alone)
AC excitation systems
Recommendation is to combine excitation systems with PSS’s (and excitation limiters)
AC excitation systems
Input signals for all power system stabilizers
ωΔfΔ
V
n
el
SP
dtdfdt
dV
AC excitation systems
Parameter ranges for AC1 excitation systems
“Shape” of response
Saturation of exciter machine
AC excitation systems
Parameter ranges for AC4 excitation systems
Limitation of control inputs
“Shape” of response
AC excitation systems
Parameter ranges for power system stabilizers
Limitation of control outputs
Static AC excitation system
Static AC excitation system
Uses generator terminals voltage, self excitation transformer and a thyristor bridge for rectification of AC signalThere are no rotating partsVarious types of controllers for regulator could be used (PI, PID, Fuzzy, Neural etc.)Widely used concept for excitation systems nowadays
Static AC excitation system
Advantages:Expanded range for excitation voltages and currents with high amplificationVery fast responseSimplicity of design (occupies small space)
Backdraws:Dependency toward the voltage occurrences Current compaundation is necessary
Static AC excitation system
There are several models for static AC excitation systems in PSS/E library:
Generic static excitation systems: EXST1/2/3, EXST2A, SCRX
Detailed static excitation systems: ESST1/2/3A ESST4B, EXELI, URST5T, ST6B
Static AC excitation system
Recommendation is to use EXST1 or ESST1A as a representation in PSS/E (with PSS and limiters)
Static AC excitation system
In case of some new excitation system installed, usually there are PI or PID controllers implemented. In such cases use ESST4B (PI controllers) or ST6B (PID controller)
Static AC excitation system
During the adjustment of the model, keep in mind:
Proportional part determines the amplification of the control signalIntegral part adjusts the time appearance of the control signal (lagging) and its rate of changeDifferential part amplifies and corrects all fast changing input signals (very sensitive value which can accelerate the change of control signal)
Static AC excitation system
Parameter ranges for ST1 excitation systems
Limitation of control inputs
“Shape” of response
Generic excitation systems
In case of absence of any knowledge about the excitation system in one power plant, use SEXS
Generic excitation systems
Avoid using SCRX, which is generic model, but used for special static excitations and it imposes “negative current logic”
Generic excitation systems
Typical values and ranges for SEXS parameters
Free to increase K up to 400
Excitation limiters
Supplementary equipment to the excitation systems
Main purpose is to readjust the operation of excitation system in “difficult regimes” of generator
Their action is restricted to maintaining of upper and lower limits for field voltage applied to rectifier unit (or to rotor winding of synchronous machine)
Excitation limiters
Recommendation for Maximum Excitation Limiters (OEL) is MAXEX1:
Excitation limiters
Recommendation for Minimum Excitation Limiters (UEL) is MNLEX1:
Excitation limiters
Minimum excitation limiter sends it’s signal to High Value Gate for comparison with the regular voltage signal. In case it is higher than the actual voltage it will superimpose and maintain the limit of low voltage
Maximum excitation limiter sends it’s signal to Low Value Gate for comparison with the regular voltage signal. In case it is lower than the actual voltage it will superimpose and maintain the limit of maximum voltage
Excitation limiters
Parameter ranges for excitation limiters
Adjustment of excitation systems
It is done according to the IEEE standards
There are two standard tests which are used in practice and modeled in PSS/E:
Open circuit testResponse Ratio Test
These tests are activated by ESTR function in PSS/E
Adjustment of excitation systems
Open Circuit test
UT
TT
nV
nEfd
EfdΔ
1V1Efd
1V
fdnfd EE ⋅<Δ 8.0
sTT 5.2≤
sT 5=
sTs U 11.0 ≤≤
After reaching the steady state, if the excitation voltage is too high compared to the terminal voltage, check the saturation factors of generator
Adjustment of excitation systems
Response Ratio test shows the capability of forcing the maximum excitation voltage on nominally loaded generator. Rising period should be over for less than 0.5 s and maximum field voltage should be at least twice the nominal value.
OEAOAOCErr
⋅−
=
Exc
itatio
n V
olta
ge
Thank youThank you