Description

This module is based on the IEEE std 412.5 type ST1A excitation system model [1]. The block diagram of a static excitation system model: the regulation is performed with a controlled rectifier, and a transformer is used for the excitation.

Mask and Parameters

AVR Parameters

ST1A-AVR mas parameters

Expanding the "ST1A diagram" displays the block diagram in the parameters window.

Name	Description	Unit
Tr	Regulator input filter time constant. This input filter is not part of the standard and there are no typical values recommended in [1]. It was added for flexibility. NB. This parameter can be set to 0 if the filter is not used.	pu
Tb, Tb1	AVR lead-lag denominator time constants	pu
Tc, Tc1	AVR lead-lag numerator time constants	pu
Ka	AVR filter gain	pu
Ta	AVR filter time constant	pu
Kf	Excitation control system stabilizer gain	pu
Tf	Excitation control system stabilizer time constant	pu
Vamax	Maximum regulator internal voltage	pu
Vamin	Minimum regulator internal voltage	pu
Vrmax	Maximum voltage regulator output	pu
Vrmin	Minimum voltage regulator output	pu
VImax	Maximum regulator input voltage	pu
VImin	Minimum regulator input voltage	pu

Exciter Parameters

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

Name	Description	Unit
KLR	Exciter output current limiter gain	pu
ILR	Exciter output current limit reference	pu
Kc	Rectifier loading factor proportional to commutating reactance	pu

Initial Values Mask Parameters

ST1A- Initial Values mask parameters

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

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
Voel^	Overexcitation limiter output	pu
Vc1	Signal proportional to compensated terminal voltage. If the Load Compensator block is not used upstream from the exciter block, then Vc1 should be connected to Vt.	pu
Vt	Machine terminal voltage	pu
Vuel^	Under-excitation limiter output*	pu
Vref	Voltage regulator reference voltage	pu
Vs	Is defined as the output voltage of a power System Stabilizer (PSS) [1]**.	pu
Ifd	Synchronous machine field current***	pu

^Vuel and Voel are normally input to this excitation system, but the user can choose to use a fixed constant value directly in the mask by choosing internal in the mask option.

*A switch allows the users to select UEL input locations

Summation point UEL ( at voltage error )
HV gate 1
HV gate 2

**A PSS input location switch

Summation point at voltage error calculation
Summation point at voltage regulator output

***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.