Description

This module is based on the IEEE std 412.5 type ST2A excitation system model [1]. The excitation system uses both terminal current and terminal voltage. The effects of commutation and rectifier loading are account in the model.

Mask and Parameters

AVR Parameters

ST2A- AVR mask parameters

Expanding the "ST2A diagram" displays the block diagram in the parameters window.

Name	Description	Unit
Tr	Regulator input filter time constant	pu
Kf	Excitation control system stabilizer gain	pu
Tf	Excitation control system stabilizer time constant	pu
Ka	Voltage regulator gain	pu
Ta	Regulator time constant	pu
Vrmax	Maximum voltage regulator output	pu
Vrmin	Minimum voltage regulator output	s

Exciter Parameters

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

ST2A- Exciter diagram

Name	Description	Unit
Te	Exciter time constant	s
Ke	Exciter constant related to self-excited field	-
Kc	Rectifier loading factor proportional to commutating reactance	-
EFDmax	Maximum exciter output voltage	pu
Kp	Potential circuit real part gain coefficient	-
Kj	Potential circuit imaginary part gain coefficient	-

Initial Values Mask Parameters

ST2A- 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 is equal to Vt (main alternator terminal voltage)	pu
Vuel	Underexcitation 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
Id	Active component of generator terminal current or component from load compensator	pu
Iq	Reactive component of generator terminal current or component from load compensator
Vd	Active component of generator terminal voltage or component from load compensator
Vq	Reactive component of generator terminal voltage or component from load compensator

*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.

*A switch allows the users to select UEL input locations (Vuel)

Summation point ( voltage error )
Take-over at voltage regulator input

**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.