Description

This model is a general-purpose rotating excitation system model that, given the proper parameters and tuning, can represent a variety of exciters. The REXSYS component was developed in line with the reference [1].

Mask and Parameters

AVR parameters

Expanding the "REXSYS AVR diagram" displays the block diagram in the parameters window.

Name	Description	Unit	Parameter range
Tr	Regulator input filter time constant	s	-
Kvp	Voltage regulator proportional gain	-	Kvp ≠ 0
Kvi	Voltage regulator integral gain	-	-
VImax	Voltage regulator input limit	pu	-
Ta	Voltage regulator time constant	s
Tc1	First stage lead-lag numerator time constant	s	-
Tb1	First stage lead-lag denominator time constant	s	-
Tc2	Second stage lead-lag numerator time constant	s	-
Tb2	Second lead-lag denominator time constant	s	-
VRmax	Maximum voltage regulator output	pu	-
VRmin	Minimum voltage regulator output	pu	-
Kf	Rate feedback gain	-	-
Tf	Rate feedback time constant	s	If Tf < 0.2, then Tf = 0.2
Tf1	Feedback lead-lag numerator time constant	s	-
Tf2	Feedback lead-lag denominator time constant	s	-
Fbf	Rate feedback signal selector	-	[1, 2, 3]

FCR and Exciter Parameters

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

Name	Description	Unit	Variable = {Possible Values}
Kip	Field current regulator proportional gain	-	-
Kii	Field current regulator integral gain	-	-
Tp	Field current bridge time constant	s	-
VFmax	Maximum exciter field current	pu	-
VFmin	Minimum exciter field current	pu	-
Kh	Field voltage controller feedback gain	-	-
Ke	Exciter constant related to self-excited field	-	-
Te	Exciter time constant	s
Kc	Rectifier loading factor proportional to commutating reactance	-	-
Kd	Exciter demagnetizing factor	-	-
Se2, Se1	Exciter saturation factor at the corresponding Vex	pu	-
Ve2,Ve1	Exciter voltage for the exciter saturation function	pu	Ve1 > Ve2 > 0
F1imf	Power supply limit factor	-	-

Initial Value Parameters

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*	Overexcitation limiter output	pu
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
Vuel*	Underexcitation limiter output	pu
Vref	Voltage regulator reference voltage	pu
Vs	Output voltage of a Power System Stabilizer (PSS)	pu
Ifd**	Synchronous machine field current	pu
Vd	d-axis component of generator terminal voltage	pu
Vq	q-axis component of generator terminal voltage	pu

*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”.

**The observable field current Ifd from the synchronous machine in HYPERSIM needs to be multiplied by the machine’s Xad = Xd – Xl prior to its input to the exciter.

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

Outputs

Name	Description	Unit
Efd	Exciter output voltage	pu

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

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

References

1. PSS®E 34.2.0 Model Library. NY, USA: Siemens Industry, Inc., 2017.

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