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AC2A


Description


This module is based on the IEEE Std 412.5 type AC2A excitation system model [1].

Mask and Parameters

AVR Parameters

*Vuel and Voel are the usual inputs for this excitation system (see Inputs, Outputs section below), but the user can choose to use a fixed constant value directly in the mask by choosing “internal” in the mask option.
Expanding the "AC2A diagram" displays the block diagram in the parameters window.


NameDescriptionUnit
Tr

Regulator input filter time constant. This input filter is not part of the standard and there are no typical values recommended. It was added for flexibility.

NB: This parameter can be set to zero if the filter is not used.


s
Tb

AVR lead-lag numerator time constant

Voltage regulator time constant


s
Tc

AVR lead-lag denominator time constant

Voltage regulator time constant


s
Ka

AVR filter gain

Voltage regulator gain


-
Ta

AVR filter time constant

Regulator time constant


s
KbSecond stage regulator gain
-
KhHigh band gain
-
KfExcitation control system stabilization gain
-
TfExcitation control system stabilizer time constant
s
VamaxMaximum regulator internal voltage
pu
VaminMinimum regulator internal voltage
pu
VrmaxMaximum voltage regulator output
pu
VrminMinimum voltage regulator output
pu

Exciter Parameters

Expanding the "Exciter diagram" displays the block diagram in the parameters window.

NameDescriptionUnit
TeExciter time constant
s
KeExciter constant related to self-excited field
-
KdDemagnetization factor
-
KcRectifier loading factor
-
Se1, Se2Exciter saturation factor at the corresponding Vex
pu
Ve1, Ve2Exciter voltage for the exciter saturation function
pu
VfemaxMaximum exciter field current
pu

Initial Value Parameters

NameDescriptionUnit
Ifd0Synchronous machine field current initial value
pu
Efd0Exciter output voltage initial value
pu

The parameters Ifd0 and Efd0 can be set manually by entering a numerical value. It can also be set automatically, based on load flow calculations, by entering a referenced synchronous machine variable.  For instance, if the name of the synchronous machine on which the excitation system is connected is “SM1”:

  • If a thermal machine or a hydraulic machine is used, Ifd0 shall be set as “=SM1.IfdInit” multiplied by the synchronous machine parameter Xad = Xd – Xl, and Efd0 shall be set as “=SM1.EfdInit”;
  • If a pu standard or pu fundamental machine is used, Ifd0 shall be set as “=SM1.IF_Init” and Efd0 shall be set as "=SM1.EFD_Init".

Inputs, Outputs and Signals Available for Monitoring

Inputs

NameDescriptionUnit
VoelOverexcitation limiter outputpu
VC1

Signal proportional to compensated terminal voltage.

If the load compensator block is not used upstream from the exciter block, then Vc1 is equal to Vt (main alternator terminal voltage)

pu
VuelUnderexcitation limiter outputpu
VrefVoltage regulator reference voltagepu
VsIs defined as the output voltage of a power system stabilizer (PSS)pu
IfdSynchronous machine field current*pu

*If a Synch. Machine (Hydraulic or Thermal) from the Network Machines and Generators library is used, the machine observable Ifd must be multiplied by the synchronous machine parameter Xad = Xd – Xl prior to its input to the exciter. This multiplication is not needed if a Synchronous Machine (pu Standard) or (pu Fundamental) is used.


The HYPERSIM® simulation option Set Initial Conditions must be checked for the automatic initialization to work properly.

Outputs

NameDescriptionUnit
EfdExciter output voltagepu

References

1. “IEEE Recommended Practice for Excitation System Models for Power System Models for Power System Stability Studies,” IEEE Standard 421.5-2005.

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