Description
This module is based on the IEEE std 412.5 type AC3A excitation system model [1]. The block diagram of this excitation system model includes an AC alternator with non-controlled rectifiers. The model presents alternate options for the under excitation limiter inputs.
Mask and Parameters
AVR Parameters
*Vuel is the usual input for this excitation system (see Inputs, Outputs section below), but the user can choose to use a fixed constant value directly in the mask by choosing “internal” in the mask option.
Expanding the "AC3A 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. It was added for flexibility. NB: This parameter can be set to zero if the filter is not used. | s | |
| Kr | Constant associated with regulator and alternator field power supply. | - | |
| Tb | AVR lead-lag numerator time constant Voltage regulator time constant | s | |
| Tc | AVR lead-lag denominator time constant Voltage regulator time constant | s | |
| Ka | AVR filter gain | - | |
| Ta | AVR filter time constant | s | |
| Kf | Excitation control system stabilizer gain | - | |
| Tf | Excitation control system stabilizer time constant | s | |
| Vamax | Maximum regulator internal voltage | pu | |
| Vamin | Minimum regulator internal voltage | pu | |
Exciter Parameters
Expanding the "Exciter diagram" displays the block diagram in the parameters window.
| Name | Description | Unit | |
|---|---|---|---|
| Ke | Exciter constant related to self-excited field | - | |
| Te | Exciter time constant | s | |
| Kc | Rectifier loading constant | - | |
| Kd | Demagnetizing factor | - | |
| Se1, Se2 | Exciter saturation factor at the corresponding Vex | pu | |
| Ve1, Ve2 | Exciter voltage for the exciter saturation function | pu | |
| Kn | Excitation system stabgilzer gain | - | |
| EFDN | Value at which feedback gain changes | pu | |
| VEmin | Minimum exciter output voltage | pu | |
| Vfemax | Maximum exciter field current | pu | |
Initial Values Mask Parameters
| Name | Description | Unit | |
|---|---|---|---|
| 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 Signals Available for Monitoring
Inputs
| Name | Description | Unit |
|---|---|---|
| Vc1 | Signal proportional to compensated terminal voltage If a 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 | Voltrage regulator reference voltage | pu |
| Vs | Is defined as the output voltage of a power system stabilizer (PSS) | pu |
| Ifd | Synchronous machine field current* | pu |
*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.