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EXAC2


Description

This model is based on the IEEE type AC2 excitation system model described in the 1981 IEEE committee report [1]. The EXAC1 component was developed in line with the references [1] [2]

Mask and Parameters

AVR parameters

Expanding the "EXAC2 diagram" displays the block diagram in the parameters window.



Name

Description

Unit

Variable = {Possible Values}

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

0 < Tr < 0.5

Tb

AVR lead-lag numerator time constant

s

0 < Tb < 20

Tc

AVR lead-lag denominator time constant

s

0 < Tc < 20

Ka

AVR filter gain

--

0 < Ka < 1000

Ta

AVR filter time constant

s

0 < Ta < 10.0

VRmax

Maximum voltage regulator output

pu

0 < Vrmax ≤ 10

VRmin

Minimum voltage regulator output

pu

-10 ≤ Vrmin < 0

Kf

Excitation control system stabilizer gain

--

0 < Kf ≤ 0.3

Tf

Excitation control system stabilizer time constant

s

0.02 < Tf < 1.5

VAmax

Maximum regulator internal voltage

pu0 < VAmax ≤ 15

VAmin

Minimum regulator internal voltage

pu-15 ≤ VAmin < 0

Kb

Second stage regulator gain

----

Kl

Exciter field current limiter gain

----

Kh

Exciter field current feedback gain

----

Vlr

Maximum exciter field current

pu--

Exciter Parameters

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

Name

Description

Unit

Variable = {Possible Values}

Ke

Exciter constant related to self-excited field

--

0 < Ke ≤ 1

Te

Exciter time constant

s

0.02 < Te < 2

Kd

Demagnetizing factor

--

0 ≤ Kd ≤ 1

Kc

Rectifier loading factor

--

0 ≤ Kc ≤ 1

Se2, Se1

Exciter saturation factor at the corresponding Vex

pu

--

Ve2,Ve1

Exciter voltage for the exciter saturation function

pu

--

Initial value tab


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

NameDescription

Type 

Voel

Over-excitation limiter output*

Input 

Vc1

Signal proportional to compensated terminal voltage (refer to the Load Compensator block documentation)

 If the Load Compensator block is not used upstream to the exciter block, then Vc1 is equal to Vt (main alternator terminal voltage)

Input 

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 

*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.

**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

NameDescription

Type 

Efd

Exciter output voltage

Output 

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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