GAST

Governor

GAST

generic

Opensource

CIM model

RMS

phasor

MRL4

Single phase

GovGAST

IEC

dynawo

#106

Author

Erwan Guichard (DPS for RTE)

Published

May 4, 2024

GAST model

Context

This governor is a standard that can apply to gas turbine model. It is a simple representations of a turbine governor control system, developed and introduced as early as the mid-1970s.

This governor model appears under the name GovGAST in the Common Information Model for Dynamics - Standard Models (2012) [1] and in the IEC 61970-302:2024 version [2].

Model use, assumptions, validity domain and limitations

This models is considered obsolete and should not be used for representing new generators and applicable existing generators. Most modern digital gas turbine governor control systems employ a proportional-integral (PI) controller that cannot be captured in this model. In It is unable to model the gas turbine operation accurately when the temperature control loop becomes active, and to replicate system oscillations around the final settling frequency. [3]

This model is constituted of a simple droop control, constant load limit (rating of turbine), only three time constants (fuel valve response, turbine response, and load limit response), and neglects all aspects of the physics of heavy-duty gas turbines.

NERC [4] and WECC recommends that generator owners and transmission planners to transition to using the GGOV1 model for generating Units currently modeled using these models. It has been removed from the NERC and WECC list of acceptable models.

Model inputs and output

The input variables are :

Variable	Description	Units
\(\omega_{Pu}\)	measured angular frequency	\(pu\) (base \(\omega_{Nom}\))
\(\omega_{RefPu}\)	reference angular frequency	\(pu\) (base \(\omega_{Nom}\))
\(P_{mRefPu}\)	reference mechanical power	\(pu\) (base \(P_{NomTurb}\))

The output signal is \(P_{mPu}\), the mechanical power in \(pu\) (base \(P_{NomTurb}\)).

Model parameters

Parameter	Description	Units
\(A_t\)	Ambient temperature load limit	\(pu\)
\(D_{Turb}\)	Turbine damping coefficient	\(pu\)
\(K_t\)	Temperature limiter gain	\(pu\)
\(R\)	Permanent droop	\(pu\)
\(t_1\)	Steam bowl time constant	\(s\)
\(t_2\)	Reheater time constant	\(s\)
\(t_3\)	Feedback time constant	\(s\)
\(V_{Max}\)	Maximum valve position	\(pu\)
\(V_{Min}\)	Minimum valve position	\(pu\)