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AC8B



Description


This module is based on the IEEE Std 412.5 type AC8B excitation system model [1]. The block diagram of this excitation system model includes an AC alternator with non-controlled rectifiers. The model presents alternate options for the under excitation limiter input.

Mask and Parameters

AVR Parameters

 


Expanding the "AC8B diagram" displays the block diagram in the parameters window.

AC8B AVR block diagram

 

NameDescriptionUnit
Tr

Regulator input 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
TdrDerivative time constant control PID
s
KprProportional gain PID control

KdrDerivative gain PID control

KirIntegral gain PID control

KaAVR filter gain
-
TaAVR filter time constant
s
VRmaxMaximum regulator internal voltage
pu
VRminMinimum regulator internal voltage
pu


Exciter Parameters


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

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

Initial Values Mask Parameters

AC8B-Initial Values mask 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".

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

Inputs and Outputs and Signals Available for Monitoring

Inputs

NameDescriptionUnit
Vc1

Signal proportional to compensated terminal voltage

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

pu
VrefVoltrage 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.

Outputs

NameDescriptionUnit
 Efd Exciter 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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