OEL2C

Authors: Erwan Guichard (DPS for RTE)

Reviewers: Lampros Papangelis (CRESYM)

IEEE OEL2C model

Context

This overexcitation limiter model first appeared in the IEEE Std 421.5-2016 (of Electrical & Engineers, 2016).

Model use, assumptions, validity domain and limitations

This model is associated to one of the voltage regulators (types AC, DC, ST) defined by the IEEE Std 421.5-2016 (of Electrical & Engineers, 2016).

The model provides an overexcitation limiter signal for the purposes of :

  • takeover : the overexcitation limiter signal acts as an upper limit on the voltage regulator main signal which then becomes the excitation voltage ;
  • summation : the overexcitation limiter signal is added to the stator voltage deviation from the reference, thus being taken into account in the calculation of the excitation voltage.

Model input and output

The input signal is either the generator field current, the generator field voltage or (for brushless excitation systems) the exciter field current, in pu.

The output signal is UOelPu, the overexcitation limiter voltage in pu (base UNom).

Model parameters

Parameter Description Unit Value (set 1) Value (set 2) Value (set 3)
C1 OEL exponent for calculation of first error - 0 0 0
C2 OEL exponent for calculation of second error - 2 2 2
FixedRd OEL fixed cooling-down time output pu -0.001 -0.001 -0.001
FixedRu OEL fixed delay time output pu 0 0 0
IInstPu OEL instantaneous field current limit pu 6 6 6
ILimPu OEL thermal field current limit pu 3 3 3
IResetPu OEL reset-reference, if OEL is inactive pu 100 100 100
ITfPu OEL reference for inverse time calculations pu 3 3 3
IThOffPu OEL reset threshold value pu 0.05 0.05 0.05
K1 OEL gain for calculation of first error pu 0 0 0
K2 OEL gain for calculation of second error pu 0.296 0.296 0.296
KAct OEL actual value scaling factor pu 1 1 1
KdOel OEL PID regulator differential gain pu 0 0 0
KFb OEL timer feedback gain pu 0 0 0
KiOel OEL PID regulator integral gain pu 0 0 1
KpOel OEL PID regulator proportional gain pu 0.5 500 0.3
Krd OEL reference ramp-down rate pu -1000 -1000 -1000
Kru OEL reference ramp-up rate pu 1000 1000 1000
KScale OEL input signal scaling factor pu - - -
Kzru OEL thermal reference release threshold pu 0.99 0.99 0.99
Sw1 If true, ramp rate depends on field current error, if false, ramp rates are fixed - - - -
tAOel OEL reference filter time constant s 0.04 0.04 0.04
tB1Oel OEL regulator first lag time constant s 0.1 2 0.1
tB2Oel OEL regulator second lag time constant s 0.1 0.1 0.1
tC1Oel OEL regulator first lead time constant s 0.1 0.2 0.1
tC2Oel OEL regulator second lead time constant s 0.1 0.1 0.1
tDOel OEL PID regulator differential time constant s 0.1 0.1 0.1
tEn OEL activation delay time s 0.2 0.2 0.2
tFcl OEL timer reference s 10 1 10
tMax OEL timer maximum level s 10 1 10
tMin OEL timer minimum level s 0 0 0
tOff OEL reset delay time s 5 5 5
tROel OEL input signal filter time constant s 0.01 0.01 0.01
VInvMaxPu OEL maximum inverse time output pu 100 100 100
VInvMinPu OEL minimum inverse time output pu 0 0 0
VOel1MaxPu Maximum OEL output limit pu (base UNom) 10 10 0
VOel1MinPu Minimum OEL output limit pu (base UNom) -10 -10 -10
VOel2MaxPu Maximum OEL lead-lag 1 output limit pu (base UNom) 100 100 0
VOel2MinPu Minimum OEL lead-lag 1 output limit pu (base UNom) -100 -100 -100
VOel3MaxPu Maximum OEL PID output limit pu (base UNom) 100 100 0
VOel3MinPu Minimum OEL PID output limit pu (base UNom) -100 -100 -100

The parameter sets correspond to an overexcitation limitation output :

  • 1 : with a takeover action at the AVR input;
  • 2 : with a takeover action at the AVR output;
  • 3 : added to the summation point in the AVR.

Model diagram

OEL2C

The OEL reference current is calculated with the following model :

OelReferenceCurrent

The OEL activation logic has three inputs (from top to bottom, IActPu, tErr, IRefPu) and one output (IBiasPu) calculated as follows :

if tErr <= 0 or (IActPu > IRefPu for a duration >= tEn) or tEn == 0
    IBiasPu = 0
elseif IRefPu == IInstPu and (IRefPu > IActPu + IThOffPu for a duration > tOff)
    IBiasPu = IResetPu
else
    IBiasPu = 0

Open source implementations

This model has been successfully implemented in :

Software URL Language Open-Source License Last consulted date Comments
Dynawo Link Modelica MPL v2.0 09/10/2024  

References

  1. of Electrical, T. I., & Engineers, E. (2016). IEEE recommended practice for excitation system models for power system stability studies . IEEE Std 421.5-2016. https://home.engineering.iastate.edu/ jdm/ee554/IEEEstd421.5-2016RecPracExSysModsPwrSysStabStudies.pdf
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