AC7B

Model Description

This device is an implementation of the IEEE type AC7B excitation system model. It is implemented as described in [1].

The AC7B model was developed in line with the references [1-3]. Figure 1 shows the architecture of the AC7B model.

FIgure 1 AC7B Architecture

Model in HYPERSIM

Figure 2 below shows the AC7B component model in HYPERSIM, and Figure 3 shows the parameters.

Figure 2 AC7B Block in HYPERSIM

Input/Output: AC7B Input/Output Parameters

Pin name	Type	Description	Units
Vref	Input	Reference voltage of the stator terminal voltage	pu
Vc1	Input	Terminal voltage of synchronous machine, transducer output
Vs	Input	Power System Stabilizer signal
Vt	Input	Terminal voltage of synchronous machine
Ifd	input	Synchronous machine field current*
Vuel	Input	Under Excitation Limiter signal
Efd	Output	The field voltage signal

*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.

AC7B AVR Tab: Parameters

Figure 3 AC7B data parameters

AC7B Exciter Tab: Parameters

Figure 4A exciter parameters

AC7B Initial Values Tab: Parameters

Default Parameters of HYPERSIM Model

The default parameters of the model developed in HYPERSIM are given in the table below.

AC7B AVR Parameters

Parameter	Unit	Description
K_PA	pu	field current regulator proportional gain
K_IA	pu/s	field current regulator integral gain
V_Amax	pu	maximum field current regulator output
V_Amin	pu	minimum field current regulator output
K_PR	s	voltage regulator proportional gain
K_IR	pu/s	voltage regulator integral gain
K_DR	pu/s	voltage regulator derivative gain
T_DR	s	lag time constant for derivative channel of PID controller
V_Rmax	pu	maximum regulator output
V_Rmin	pu	minimum regulator output
K_p	pu	potential circuit gain coefficient
K_L	pu	gain related to negative exciter field current capability

AC7B Excitor Parameters

Parameter	Unit	Description
K_E	pu	exciter gain
T_E	s	exciter time constant
K_F1	pu	excitation control system stabilizer gain
K_F2	pu
K_F3	pu
T_F	s	excitation control system stabilizer time constant
V_FEMAX	pu	exciter field current limit
V_FEMIN	pu	minimum of exciter voltage back of commutating reactance
K_D	pu	demagnetizing factor
K_C	pu	rectifier loading factor
V_E1	pu	The exciter voltage point which is near the exciter ceiling voltage
V_E2	pu	The exciter voltage point which is near 75% of VE1
SE_V_E1	pu	The exciter saturation function value at VE1
SE_V_E2	pu	The exciter saturation function value at VE2

AC7B initial value parameters

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.

References

“IEEE Recommended Practice for Excitation System Models for Power System Models for Power System Stability Studies,” IEEE Standard 421.5-2005.
Kundur, “Power System Stability and Control”, McGraw-Hill 1994
Standard Dynamic Turbine-Governor Systems in NEPLAN Power System Analysis Tool
PSSE Explore 34 Siemens software