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ST1A



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.

 

NameDescriptionUnit

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.

ST1A Exciter diagram

NameDescriptionUnit

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

NameDescriptionUnit

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
VtMachine terminal voltagepu

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

NameDescriptionUnit
 Efd Exciter output voltagepu

References

1. “IEEE Recommended Practice for Excitation System Models for Power System Models for Power System Stability Studies,” IEEE Standard 421.5-2005.

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