Description

This model is based on the IEEE type AC1 excitation system model described in the 1981 IEEE committee report [1]. The EXAC1 component was developed in line with the references [1] [2]

Mask and Parameters

AVR parameters

Expanding the "EXAC1 diagram" displays the block diagram in the parameters window.

Name	Description	Unit	Variable = {Possible Values}
Tr	Regulator input filter time constant. This input filter is not part of the IEEE committee report and there are no typical values recommended in [1]. It was added for flexibility. N.B. This parameter can be set to “0” if the filter is not used.	s	0 < Tr < 0.5
Tb	AVR lead-lag numerator time constant	s	0 < Tb < 20
Tc	AVR lead-lag denominator time constant	s	0 < Tc < 20
Ka	AVR filter gain	--	0 < Ka < 1000
Ta	AVR filter time constant	s	0 < Ta < 10.0
VRmax	Maximum voltage regulator output	pu	0 < Vrmax ≤ 10
VRmin	Minimum voltage regulator output	pu	-10 ≤ Vrmin < 0
Kf	Excitation control system stabilizer gain	--	0 < Kf ≤ 0.3
Tf	Excitation control system stabilizer time constant	s	0.02 < Tf < 1.5

Exciter Parameters

Name	Description	Unit	Variable = {Possible Values}
Ke	Exciter constant related to self-excited field	--	0 < Ke ≤ 1
Te	Exciter time constant	s	0.02 < Te < 2
Kd	Demagnetizing factor	--	0 ≤ Kd ≤ 1
Kc	Rectifier loading factor	--	0 ≤ Kc ≤ 1
Se2, Se1	Exciter saturation factor at the corresponding Vex	pu	--
Ve2,Ve1	Exciter voltage for the exciter saturation function	pu	--

Initial value tab

Name	Description	Unit	Variable = {Possible Values}
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 Additional Signals Available for Monitoring

Inputs

Name	Description	Type
Voel	Over-excitation limiter output*	Input
Vc1	Signal proportional to compensated terminal voltage (refer to the Load Compensator block documentation) If the Load Compensator block is not used upstream to the exciter block, then Vc1 is equal to Vt (main alternator terminal voltage)	Input
Vuel	Under-excitation limiter output*	Input
Vref	Voltage regulator reference voltage	Input
Vs	Is defined as the output voltage of a Power System Stabilizer (PSS) [1].	Input
Ifd	Synchronous machine field current**	Input

*Vuel and Voel is normally an input to this excitation system but the user has the option to use a fixed constant value directly in the mask by choosing internal in the mask option.

**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	Type
Efd	Exciter output voltage	Output

References

[1] I. C. Report, "Excitation System Models for Power System Stability Studies," in IEEE Transactions on Power Apparatus and Systems, vol. PAS-100, no. 2, pp. 494-509, Feb. 1981.

[2] PSS®E 34.2.0 Model Library. NY, USA: Siemens Industry, Inc., 2017.