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

Name	Description	Unit
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
Tdr	Derivative time constant control PID	s
Kpr	Proportional gain PID control
Kdr	Derivative gain PID control
Kir	Integral gain PID control
Ka	AVR filter gain	-
Ta	AVR filter time constant	s
VRmax	Maximum regulator internal voltage	pu
VRmin	Minimum regulator internal voltage	pu

Exciter Parameters

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

Name	Description	Unit
Ke	Exciter constant related to self-excited field	-
Te	Exciter time constant	s
Kc	Rectifier loading factor	-
Kd	Demagnetizing factor	-
Se1, Se2	Exciter saturation factor at the corresponding Vex	pu
Ve1, Ve2	Exciter voltage for the exciter saturation function	pu
VEmin	Minimum exciter output voltage	pu
Vfemax	Maximum exciter field current	pu

Initial Values Mask Parameters

AC8B-Initial Values mask parameters

Name	Description		Unit
Ifd0	Synchronous machine field current initial value		pu
Efd0	Exciter 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

Name	Description	Unit
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
Vref	Voltrage regulator reference voltage	pu
Vs	Is defined as the output voltage of a power system stabilizer (PSS)	pu
Ifd	Synchronous 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

Name	Description	Unit
Efd	Exciter output voltage	pu

References

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