Description

This model is a compound source controlled-rectifier excitation system based on the IEEE type ST3 excitation system model described in the 1981 IEEE committee report [1]. The EXST3 component was developed in line with the references [1] [2].

Mask and Parameters

AVR parameters

Expanding the "EXST3 diagram" displays the block diagram in the parameters window.

Name	Description	Unit	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	--
Kj	Voltage regulator gain	--	--

Exciter Parameters

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

Name	Description	Unit	Parameter Range
EFDmax	Maximum exciter output voltage	pu	--
Kg	Feedback gain constant of the inner loop field regulator	-	--
VGmax	Maximum inner loop voltage feedback	pu	--
Kp	Potential circuit real part gain coefficient	-	--
Ki	Potential circuit imaginary part gain coefficient	-	--
Kc	Rectifier loading factor proportional to commutating reactance	-	--
Xl	Reactance associated with potential source	pu	--
ThetaP	Potential circuit phase angle	Degrees	--

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	Unit
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
Id	d-axis component of generator terminal current	Input
Iq	q-axis component of generator terminal current	Input
Vd	d-axis component of generator terminal voltage	Input
Vq	q-axis component of generator terminal voltage	Input
Ifd**	Synchronous machine field current	Input

*Vuel and Voel are normally inputs 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.
**The observable field current Ifd from the synchronous machine in HYPERSIM needs to be multiplied in its current version by the machine’s Xad = Xd – Xl prior to its input to the exciter if a thermal machine or a hydraulic machine is used. This multiplication is not required if a pu standard or pu fundamental machine is used.

Outputs

Name	Description	Unit
Efd	Exciter output voltage	pu

The terminal current calculation is performed in terms of Id and Iq using the following equation:

Similarly, the terminal voltage calculation is performed in terms of Vd and Vq using the following equation:

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.