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EXST1

This model is based on the IEEE type ST1 excitation system model described in the 1981 IEEE committee report [1]. The EXST1 component was developed in line with the references [1] [2].

Symbol

Mask parameters

Exciter tab



Name

Description

Unit

Hard coded 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

--

Kf

Excitation control system stabilizer gain

--

--

Tf

Excitation control system stabilizer time constant

s

Tf > 0.3,

otherwise Tf = 0.3

Kc

Rectifier loading factor

--

--

Initial value tab

Name

Description

Unit

Hard coded parameter range

Efd0

Exciter output voltage initial value

pu

--

The parameter 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”:

  • Efd0 shall be set as “=SM1.EfdInit” if a thermal machine or a hydraulic machine is used;
  • Efd0 shall be set as "=SM1.EFD_Init" if a pu standard or pu fundamental machine is used.

The HYPERSIM simulation option “Set Initial Conditions” must be checked for the automatic initialization to work properly.

Input/Output signals

The model’s inputs and outputs are described in the following table:

NameDescription

Type 

Voel*

Over-excitation limiter output

Input 

Vc1

Signal proportional to compensated terminal voltage. If the Load Compensator block is not used upstream to the exciter block, then Vc1 must be connected to Vt of the machine.

Input 

VtMachine terminal voltageInput

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 

Ifd**

Synchronous machine field current

Input 

Efd

Exciter output voltage

Output 

* 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”.

**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.

Sensor descriptions

NameDescriptionUnit
EfdField voltagepu
IfdField currentpu
Vc1Terminal voltagepu
VoelOver-excitation limiter outputpu
VrefVoltage regulator reference voltagepu
VsOutput voltage of power system stabilizerpu
VuelUnder-excitation limiter outputpu

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.

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