This model is based on the IEEE type ST1 excitation system model described in the 1981 IEEE committee report [1]. The EXST1 component was developed in line with the references [1] [2].

Symbol

Mask parameters

Exciter tab

Name	Description	Unit	Hard coded parameter range
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	--
VImax	Maximum regulator input voltage	pu	--
VImin	Minimum regulator input voltage	pu	--
Tb	AVR lead-lag numerator time constant	s	--
Tc	AVR lead-lag denominator time constant	s	--
Ka	AVR filter gain	--	--
Ta	AVR filter time constant	s	--
VRmax	Maximum voltage regulator output	pu	--
VRmin	Minimum voltage regulator output	pu	--
Kf	Excitation control system stabilizer gain	--	--
Tf	Excitation control system stabilizer time constant	s	Tf > 0.3, otherwise Tf = 0.3
Kc	Rectifier loading factor	--	--

Initial value tab

Name	Description	Unit	Hard coded parameter range
Efd0	Exciter output voltage initial value	pu	--

The parameter 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”:

Efd0 shall be set as “=SM1.EfdInit” if a thermal machine or a hydraulic machine is used;
Efd0 shall be set as "=SM1.EFD_Init" if a pu standard or pu fundamental machine is used.

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

Input/Output signals

The model’s inputs and outputs are described in the following table:

Name	Description	Type
Voel*	Over-excitation limiter output	Input
Vc1	Signal proportional to compensated terminal voltage. If the Load Compensator block is not used upstream to the exciter block, then Vc1 must be connected to Vt of the machine.	Input
Vt	Machine 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
Efd	Exciter output voltage	Output

^*Vuel and Voel are normally inputs to the excitation system but the user has the option to use a fixed constant value directly in the component mask by choosing “internal”.

^**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.

Sensor descriptions

Name	Description	Unit
Efd	Field voltage	pu
Ifd	Field current	pu
Vc1	Terminal voltage	pu
Voel	Over-excitation limiter output	pu
Vref	Voltage regulator reference voltage	pu
Vs	Output voltage of power system stabilizer	pu
Vuel	Under-excitation limiter output	pu

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.