Custom Governor Models

This page documents the custom turbine-governor (tor_) models in RAMSES. These models are implemented in Fortran using the legacy multi-subroutine API and cover a wide range of prime-mover types: thermal (steam), gas turbine, hydraulic, nuclear, and simplified equivalents.

Usage in Dynamic Data Files

Governor/torque models in RAMSES are defined as sub-records within a SYNC_MACH block using the TOR keyword, followed by the model name and its parameters. They are not standalone records. The TOR line appears after the EXC (exciter) line, and the ; at the end closes the entire SYNC_MACH block.

SYNC_MACH name bus FP FQ P Q SNOM Pnom H D IBRATIO
                    XT  Xl  Xd  X'd  X"d  Xq  X'q  X"q  m  n  Ra  T'do  T"do  T'qo  T"qo
              EXC model_name  param1  param2  ...
              TOR model_name  param1  param2  ... ;

This page documents the four governors built into every RAMSES distribution, CONSTANT, 1ST_ORDER, HYDRO_GENERIC1 and THERMAL_GENERIC1, which take no prefix and are written in uppercase, together with HYDRO_DG, registered since 3.76.

It also documents GASTURBM, GOVCLASM, GOVHYDR and GOVNUC, which the family dispatcher has handled directly since 3.79. Before 3.79 they were compiled under no name and RAMSES rejected them in a data file.

The IEEE governors, DEGOV1, ENTSOE_simp, GAST, TGOV1 and HYGOV, are on the IEEE Governors page. For the whole catalogue at a glance, see the Model Reference index.

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CONSTANT (tor_constant)

The data-file model name is CONSTANT.

Scientific Description

The tor_constant model provides a constant mechanical torque source. The mechanical torque is fixed at its initialisation value and does not respond to speed deviations or load changes:

$$T_m(t) = T_{m0} \quad \forall t$$

The single algebraic state satisfies:

$$f(1) = x(1) - T_{m0} = 0$$

The observable output is mechanical power:

$$P_m = T_m \cdot \omega$$

Implementation details:

• nbxvar = 1, nbzvar = 0, nbdata = 0
• One additional parameter: prm(1) = Tm0 (set at initialisation from load-flow)
• Observable: Pm = x(1) * omega

Parameters

Parameter	Description
(none)	No user-supplied parameters. $T_{m0}$ is taken from the load-flow initialisation.

Usage Example

RAMSES Data File

SYNC_MACH g6  g6  1. 1.  0.  0.   400. 360. 6. 0. 2.05
                    XT   0.15  2.2  0.3    0.2   2.   0.4  0.2  0.1  6.0257  0.  7.00  0.05  1.5  0.05
              EXC GENERIC1   3.0618 -0.1  1.  0.  100. -1. -20.0  10.  120. 5.  12.5 0.1  0.  5.
                                1     75.   15.    0.22    0.012     0.22    0.012    -0.1    0.1
              TOR CONSTANT ;

Notes

• Useful for machines operating at fixed setpoint, for testing generator models in isolation, or as a placeholder.
• The mechanical power observable $P_m = T_m \cdot \omega$ will vary slightly with speed changes.
• TOR CONSTANT takes no parameters, $T_{m0}$ is set automatically from the load-flow initialisation.

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1ST_ORDER (tor_1storder)

The data-file model name is 1ST_ORDER (uppercase, with the underscore).

Scientific Description

The tor_1storder model is a first-order speed governor with droop and a two-mass (HP/LP) turbine representation. It captures the primary frequency response through a proportional-droop speed controller with a first-order lag.

Speed controller with droop $R$:

The mechanical torque setpoint is:

$$T_{set} = T_{m0} - \frac{\omega - 1}{R}$$

The HP torque tracks $T_{set}$ through a first-order lag with time constant $T_2$:

$$\frac{d x_1}{dt} = \frac{1}{T_2}\left(T_{set} - x_1\right)$$

The LP (shaft) torque is a weighted combination:

$$x_2 = (1 - F_{HP}) \cdot x_1 + F_{HP} \cdot T_{set}$$

where $F_{HP}$ is the fraction of power generated in the HP stage.

From the Fortran equations:

f(1) = (-x(1) + (prm(4) - (omega-1.d0)/prm(3))) / prm(2)
f(2) = (1.d0-prm(1))*x(1) + prm(1)*(prm(4)-(omega-1.d0)/prm(3)) - x(2)

i.e.:

• prm(1) = FHP (HP fraction), prm(2) = T2 (time constant), prm(3) = R (droop)
• prm(4) = Tm0 (setpoint, set at init)

Implementation details:

• nbxvar = 2, nbzvar = 0, nbdata = 3
• State 1 = HP torque x(1), State 2 = LP torque x(2)
• Observables: HP torque, LP torque

Parameters

Parameter	Description
FHP	Fraction of torque produced by the HP turbine stage (0–1)
T2	Governor/HP turbine time constant (s)
R	Speed droop (pu/pu)

Usage Example

RAMSES Data File

SYNC_MACH g1  g1  1. 1.  0.  0.   800. 760. 3. 0. 0.95
                    XT   0.15  1.1  0.25   0.2   0.7   *   0.2  0.1  6.0257  0.  5.00  0.05  *  0.1
              EXC GENERIC1   1.8991 -0.1  0.  1.  100. -1. -11  10.  70.  10.  20. 0.1  0.  4.
                                1     75.   15.    0.2    0.01     0.2    0.01    -0.1    0.1
              TOR 1ST_ORDER  0.30  0.50  0.05 ;  ! FHP  T2  R

Notes

• FHP = 0 makes the model a pure first-order lag on the total torque.
• FHP = 1 bypasses the HP lag entirely; the torque instantly tracks the droop setpoint.
• Typical primary-frequency response studies use R = 0.04–0.05.

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THERMAL_GENERIC1 (tor_thermal_generic1)

The data-file model name is THERMAL_GENERIC1.

Scientific Description

The tor_thermal_generic1 model is a generic multi-stage steam turbine governor, suitable for both single-shaft and cross-compound units. It includes a speed controller with rate-limiting, a three-section steam chest/reheater, and separate HP, MP, and LP turbine stages.

Speed governor:

The speed deviation is divided by the droop $\sigma$ and measured with time constant $T_{mes}$:

$$T_{mes}\,\dot{x}_1 = -x_1 + \frac{\omega - 1}{\sigma}$$

The gate demand is what remains of the power setpoint after that term and the current gate position are taken off:

$$e_{gov} = P_0 - x_1 - z$$

It is divided by the servo time constant $T_{sm}$, rate-limited to $[zdot_{min},\, zdot_{max}]$, and integrated into the gate opening $z$ within $[z_{min},\, z_{max}]$.

Turbine power stages:

The gate opening drives three lags in series, the reheat stage carrying the intercept valve factor $ivo$:

$$T_{hp}\,\dot{x}_{hp} = -x_{hp} + z, \qquad T_r\,\dot{x}_r = -x_r + x_{hp}, \qquad T_{lp}\,\dot{x}_{lp} = -x_{lp} + ivo\,x_r$$

Each stage contributes its own fraction of the power, and the three fractions sum to one:

$$P_{mHP} = F_{hp}\,x_{hp}, \qquad P_{mMP} = F_{mp}\,ivo\,x_r, \qquad P_{mLP} = (1 - F_{hp} - F_{mp})\,x_{lp}$$

Total mechanical power, and the torque delivered to the shaft:

$$P_m = P_{mHP} + P_{mMP} + P_{mLP}, \qquad T_m = \frac{P_m}{\omega}$$

Parameters:

Parameter	Index	Description
sigma	1	Speed droop (pu/pu)
Tmes	2	Speed measurement time constant (s)
Tsm	3	Servo/gate time constant (s)
zdotmin	4	Minimum gate rate (pu/s)
zdotmax	5	Maximum gate rate (pu/s)
zmin	6	Minimum gate opening (pu)
zmax	7	Maximum gate opening (pu)
Thp	8	HP turbine time constant (s)
Fhp	9	HP power fraction
Tr	10	Reheater / MP time constant (s)
Fmp	11	MP power fraction
Tlp	12	LP turbine time constant (s)

Implementation details:

• nbxvar = 10, nbzvar = 2, nbdata = 12, nbaddpar = 2
• Additional: prm(13) = P0 (initial power), prm(14) = ivo (intercept valve factor)

Caution

ivo is an additional parameter: it is computed at initialisation rather than read from the record, and the engine sets it to 1 unconditionally. The intercept valve factor is therefore always 1 and cannot be given another value from a data file.

• Observables: z, PmHP, PmMP, PmLP, Pm

Usage Example

RAMSES Data File

SYNC_MACH g1  g1  1. 1.  0.  0.   800. 760. 3. 0. 0.95
                    XT   0.15  1.1  0.25   0.2   0.7   *   0.2  0.1  6.0257  0.  5.00  0.05  *  0.1
              EXC GENERIC1   1.8991 -0.1  0.  1.  100. -1. -11  10.  70.  10.  20. 0.1  0.  4.
                                1     75.   15.    0.2    0.01     0.2    0.01    -0.1    0.1
              TOR THERMAL_GENERIC1  0.05  0.02  0.20  -0.10  0.10  0.0  1.05  0.30  0.30  7.0  0.40  0.50 ;
              !                     sigma Tmes  Tsm  zdotmin zdotmax zmin zmax  Thp   Fhp   Tr   Fmp   Tlp

Notes

• The LP fraction is 1 - Fhp - Fmp; ensure Fhp + Fmp ≤ 1.
• Set Tmes = 0 to bypass the speed measurement filter (instantaneous speed sensing).
• Rate limits zdotmin/zdotmax are critical for AGC studies.

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HYDRO_GENERIC1 (tor_hydro_generic1)

The data-file model name is HYDRO_GENERIC1.

Scientific Description

The tor_hydro_generic1 model is a generic hydraulic turbine governor with a penstock (water column) and PI controller. It implements the standard hydraulic governor structure following IEEE Std 1110 conventions.

PI speed governor:

The speed error with droop $\sigma$:

$$e = (P_0 - P_{meas}) \cdot \sigma + (1 - \omega)$$

A PI controller with gains $K_P$ and $K_I$ drives the gate demand:

$$\dot{x}_{I} = K_I \cdot e$$ $$z_{demand} = K_P \cdot e + x_I$$

The gate is rate-limited by $LIM_{\dot{z}}$ and position-limited by $[0, 1]$, with a servo time constant $T_{sm}$.

Water column (penstock):

The flow $Q$ and head $H$ are related by the water-starting time $T_W$:

$$T_W \cdot \frac{dQ}{dt} = 1 - H$$

The head is:

$$H = \left(\frac{Q_{v} + T_m (1 - Q_v)}{z}\right)^2$$

where $Q_v$ is the no-load flow fraction.

Turbine mechanical torque:

$$T_m = \sqrt{H} \cdot (Q - Q_v \cdot \sqrt{H})$$ $$P_m = T_m \cdot \omega$$

Parameters:

Parameter	Index	Description
SIGMA	1	Speed droop (pu/pu)
Tmes	2	Speed measurement time constant (s)
Qv	3	No-load water flow fraction (pu)
KP	4	PI proportional gain
KI	5	PI integral gain
TSM	6	Gate servo time constant (s)
LIMZDOT	7	Gate velocity limit (pu/s)
TW	8	Water starting time (s)

Implementation details:

• nbxvar = 6, nbzvar = 2, nbdata = 8, nbaddpar = 1
• Additional: prm(9) = P0 (initial electrical power)
• Observables: z, Q, H, Pm

Usage Example

RAMSES Data File

SYNC_MACH g1  g1  1. 1.  0.  0.   800. 760. 3. 0. 0.95
                    XT   0.15  1.1  0.25   0.2   0.7   *   0.2  0.1  6.0257  0.  5.00  0.05  *  0.1
              EXC GENERIC1   1.8991 -0.1  0.  1.  100. -1. -11  10.  70.  10.  20. 0.1  0.  4.
                                1     75.   15.    0.2    0.01     0.2    0.01    -0.1    0.1
              TOR HYDRO_GENERIC1  0.04  2.0  0.  2.00  0.40  0.2  0.1  1.0 ;
              !                   SIGMA  TP  Qv   KP    KI   TSM LIMZDOT TW

Notes

• TW (water-starting time) is the most influential parameter; typical values are 0.5–3 s.
• Increase KP / KI carefully: large values can cause governor instability with high TW.
• Qv = 0 assumes no no-load losses.
• Parameters follow the order in dyn_A.txt: SIGMA TP Qv KP KI TSM LIMZDOT TW.

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HYDRO_DG (tor_HYDRO_DG)

The data-file model name is HYDRO_DG. Registered since 3.76.

Scientific Description

A hydraulic turbine governor for a dispersed generation unit that holds an active-power setpoint and does not provide primary frequency response.

The penstock and turbine are exactly those of HYDRO_GENERIC1. What differs is the governor control law, and the difference is the point of the model. HYDRO_GENERIC1 is a speed governor: its error signal carries an unconditional frequency term, so the unit responds to system frequency whether or not that is wanted. HYDRO_DG regulates power alone.

PI power regulator:

The error is the deviation from the setpoint captured at initialisation, with no droop term and no speed term:

$$e = P^{*} - P$$ $$\dot{x}_{I} = K_i \cdot e, \qquad z_{demand} = K_p \cdot e + x_{I}$$

There is no measurement lag on $P$, so the regulator acts on the instantaneous electrical power. The gate follows through a servo of time constant $T_{sm}$, rate-limited to $\pm LIM_{\dot{z}}$ and position-limited to $[0, 1]$.

Water column and turbine, identical to HYDRO_GENERIC1:

$$T_W \cdot \frac{dQ}{dt} = 1 - H, \qquad H = \left(\frac{Q}{z}\right)^{2}$$ $$T_m \cdot \omega = \frac{(Q - Q_v) \, H}{1 - Q_v}$$

Parameters:

Parameter	Index	Description
Qv	1	No-load water flow fraction (pu)
Kp	2	PI proportional gain
Ki	3	PI integral gain
TSM	4	Gate servo time constant (s)
LIMZDOT	5	Gate velocity limit (pu/s)
TW	6	Water starting time (s)

These are exactly parameters 3 to 8 of HYDRO_GENERIC1, in the same order. HYDRO_GENERIC1 precedes them with SIGMA (droop) and Tmes (speed measurement lag), and those two are what HYDRO_DG does not have. Setting SIGMA to zero in HYDRO_GENERIC1 does not reproduce HYDRO_DG, because the frequency term survives.

Implementation details:

• nbxvar = 5, nbzvar = 2, nbdata = 6, nbaddpar = 1
• Additional: prm(7) = Pset, the initial electrical power, captured at initialisation
• Observables: z, Q, H, Pm, Pset

Usage Example

RAMSES Data File

SYNC_MACH G4  N4 1. 1.  0.  0. 5 4.5 3. 0. 1.9333
              XT  0.0937  2.027  0.210  0.173  2.027  *  0.173  0.1  6  0.00  3.1  0.0387  *  0.0387
              EXC AVR_DG  2.865 -0.1  0.  1.  100. -1. -20  10  50  4  20  0.1  0  5
                          1  0.  5.  1.  1.  1.  1.  0.  0.
                          0.04  0.06  -0.2  0.33
              TOR HYDRO_DG  0.0  0.1  0.4  0.2  0.1  1.0 ;
              !             Qv   Kp   Ki   TSM LIMZDOT TW

Notes

• The setpoint is not a parameter. Pset is captured from the power-flow solution at initialisation, so the unit holds whatever it was dispatched to.
• Because there is no frequency term, a system built only of these units has no primary frequency control. That is deliberate for dispersed generation studies, and it is worth being explicit about when interpreting a frequency response.
• Qv = 0 assumes no no-load losses.
• The head relation divides by the gate position, which is floored at 1e-3 in the implementation so a fully closed gate cannot produce a division by zero.

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tor_gasturbm

Note

Callable since 3.79. Earlier releases compiled this model under no name, so a data file referring to it was rejected.

Scientific Description

The tor_gasturbm model is a gas turbine governor following a multi-stage combustion model. It captures the compressor, fuel system, combustion chamber delay, and turbine torque characteristic. The name suffix m indicates a modified version.

Speed governor:

The governor error drives a PI controller producing a fuel demand signal. The speed governor uses:

$$e_{gov} = (\omega_{ref} - \omega) / TDSP - STAT \cdot P_{elec}$$

with saturation limits $[MIN,\, MAX]$.

Fuel system and combustion:

The fuel valve position g1 is driven through:

• A speed governor with gain $ZZ$ and lead–lag time constants determined by $XX$, $YY$
• A fuel flow path through first-order lag $TVALVE$
• Combustion chamber lag $TGAZ$

Turbine output:

The turbine mechanical power follows:

$$P_m = BF2 \cdot g_{comb} + AF2$$

where $g_{comb}$ is the combustion output through lag $TCD$.

Additional thermodynamic correction terms involve $TF$ (flame lag) and $ECR$ (exhaust correction ratio).

Parameters from Fortran source (prm array):

Index	Name	Description
1	TDSP	Speed droop time constant (s)
2	STAT	Steady-state gain
3	ZZ	Governor proportional gain
4	XX	Lead numerator factor
5	YY	Lag denominator factor
6	SACC	Acceleration constant
7	MIN	Minimum fuel valve position (pu)
8	MAX	Maximum fuel valve position (pu)
9	TVALVE	Fuel valve time constant (s)
10	TGAZ	Combustion chamber time constant (s)
11	TF	Flame lag time constant (s)
12	ECR	Exhaust correction ratio
13	TCD	Compressor discharge time constant (s)
14	BF2	Turbine power output slope
15	AF2	Turbine power output intercept (pu)

Implementation details:

• nbxvar = 10, nbzvar = 4, nbdata = 15, nbaddpar = 1
• Additional: prm(16) = SETPOINT (initialised from load-flow power)
• Observables: g2, x4, g1

Usage Example

RAMSES Data File

SYNC_MACH g1  g1  1. 1.  0.  0.   800. 760. 3. 0. 0.95
                    XT   0.15  1.1  0.25   0.2   0.7   *   0.2  0.1  6.0257  0.  5.00  0.05  *  0.1
              EXC GENERIC1   1.8991 -0.1  0.  1.  100. -1. -11  10.  70.  10.  20. 0.1  0.  4.
                                1     75.   15.    0.2    0.01     0.2    0.01    -0.1    0.1
              TOR GASTURBM  0.05  1.0  25.0  0.50  1.0  1.0  0.0  1.0  0.05  0.40  0.01  0.0  0.20  1.0  0.0 ;
              !              TDSP STAT  ZZ    XX   YY  SACC MIN  MAX TVALVE TGAZ   TF   ECR   TCD  BF2  AF2

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tor_govclasm

Note

Callable since 3.79. Earlier releases compiled this model under no name, so a data file referring to it was rejected.

Scientific Description

The tor_govclasm model is a classical thermal governor with a composite control law including deadband, droop, integral control, and combustion dynamics. The name stands for “governor classical model”.

Speed governor with deadband and droop:

The speed error passes through a deadband $[DBON, DEADB]$ before entering a proportional–integral controller. The integral path has saturation at $MAXINT$ and gain $ALPHA$. The reset time $TRES$ determines the integration rate.

Valve and combustion dynamics:

The valve demand passes through:

1. A governor integrator with time constant $TSM$, its rate held inside $[VFN,\, V0]$
2. A first-order lag $TFV$ (valve actuator)
3. A rate limiter $[PVARMIN,\, PVARMAX]$ (with gain $GPVAR$) representing fuel response
4. A combustion/steam chest lag $KCR$, $TCR$ producing fuel flow
5. Lower bound: $MINFUEL$
6. Transport delay $TDELAY$ (approximated)
7. Turbine output through lag $TCH$ with limits $[PMIN,\, PMAX]$

Parameters from Fortran source (prm array):

Index	Name	Description
1	STAT	Governor static characteristic selector
2	DEADB	Deadband half-width (pu)
3	DBON	Deadband onset (pu)
4	TSM	Speed measurement / filter time constant (s)
5	V0	Maximum valve opening rate, upper limit on the governor integrator rate (pu/s)
6	VFN	Minimum valve rate, applied directly as the lower bound, so normally negative (pu/s)
7	TFV	Valve actuator time constant (s)
8	VFR	Fuel flow rate limit (pu/s)
9	MAXINT	Maximum integral output (pu)
10	ALPHA	Integral controller gain
11	TRES	Integral reset time (s)
12	GOMP	Governor proportional gain
13	PVARMAX	Maximum power variation rate (pu)
14	PVARMIN	Minimum power variation rate (pu)
15	GPVAR	Power variation gain
16	KCR	Combustion gain
17	TCR	Combustion time constant (s)
18	MINFUEL	Minimum fuel flow (pu)
19	TDELAY	Combustion transport delay (s)
20	PMAX	Maximum turbine output (pu)
21	TCH	Steam chest / turbine lag (s)
22	PMIN	Minimum turbine output (pu)

Implementation details:

• nbxvar = 6, nbzvar = 10, nbdata = 22, nbaddpar = 1
• Additional: prm(23) = P0 (initialised from load-flow power)
• Observables: x2, b3, b4

Usage Example

RAMSES Data File

SYNC_MACH g1  g1  1. 1.  0.  0.   800. 760. 3. 0. 0.95
                    XT   0.15  1.1  0.25   0.2   0.7   *   0.2  0.1  6.0257  0.  5.00  0.05  *  0.1
              EXC GENERIC1   1.8991 -0.1  0.  1.  100. -1. -11  10.  70.  10.  20. 0.1  0.  4.
                                1     75.   15.    0.2    0.01     0.2    0.01    -0.1    0.1
              TOR GOVCLASM  1.0  0.003  0.001  0.10  1.0  1.0  0.30  0.5  1.0  1.0  5.0  25.0  0.10  -0.10  0.05  1.0  0.20  0.05  0.30  1.05  0.30  0.05 ;
              !              STAT DEADB  DBON   TSM   V0  VFN   TFV  VFR MAXINT ALPHA TRES  GOMP PVARMAX PVARMIN GPVAR KCR  TCR MINFUEL TDELAY PMAX  TCH  PMIN

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tor_govhydr

Note

Callable since 3.79. Earlier releases compiled this model under no name, so a data file referring to it was rejected.

Scientific Description

The tor_govhydr model is a simplified hydraulic governor with PI control and a non-linear penstock. It differs from tor_hydro_generic1 in its simplified turbine characteristic and simpler water-column formulation.

PI governor:

$$\dot{x}_2 = K_I \cdot e, \quad x_2 \in [0, 1]$$ $$z_{demand} = K_P \cdot e + x_2$$

where the speed error $e = P_0/\omega - T_m - \omega \cdot STAT + \ldots$ accounts for the droop and steady-state bias.

Penstock (two-lag water column):

$$T_{CE1} \cdot \frac{dx_3}{dt} = P - x_3(1 + T_{CE2}/T_{CE1})$$

The turbine mechanical power is computed via an empirical quadratic:

$$P_m = 1.35 \cdot z - 0.7 z^2$$

derived from the non-linear head-flow curve approximated at initialisation.

Parameters from Fortran source:

Index	Name	Description
1	STAT	Steady-state gain selector
2	KP	Proportional gain
3	KI	Integral gain
4	TC	Governor/servo time constant (s)
5	V0	Maximum gate opening rate, upper limit on gate velocity (pu/s)
6	VF	Maximum gate closing rate, entered as a positive magnitude and applied as $-V_F$ (pu/s)
7	TCE2	Second penstock time constant (s)
8	TCE1	First penstock time constant (s)

Implementation details:

• nbxvar = 4, nbzvar = 4, nbdata = 8, nbaddpar = 1
• Additional: prm(9) = P0 (initialised from load-flow power)
• No observables defined (nbobs = 0)

Usage Example

RAMSES Data File

SYNC_MACH g1  g1  1. 1.  0.  0.   800. 760. 3. 0. 0.95
                    XT   0.15  1.1  0.25   0.2   0.7   *   0.2  0.1  6.0257  0.  5.00  0.05  *  0.1
              EXC GENERIC1   1.8991 -0.1  0.  1.  100. -1. -11  10.  70.  10.  20. 0.1  0.  4.
                                1     75.   15.    0.2    0.01     0.2    0.01    -0.1    0.1
              TOR GOVHYDR  1.0  2.0  0.5  0.10  1.0  1.0  1.0  5.0 ;
              !             STAT  KP   KI   TC   V0   VF  TCE2 TCE1

Notes

• TCE1 corresponds roughly to the water-starting time $T_W$.
• TCE2/TCE1 sets the ratio of the two penstock lags.

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tor_govnuc

Note

Callable since 3.79. Earlier releases compiled this model under no name, so a data file referring to it was rejected.

Scientific Description

The tor_govnuc model is a nuclear plant governor with deadband, droop, integral control, and a non-linear turbine characteristic via GOMP (the gain of the output multiplier). It is structurally similar to tor_govclasm but tailored for the slower, tightly-regulated dynamics of nuclear steam supply systems.

Speed governor:

The speed error passes through a deadband $[DBON, DEADB]$:

$$e = \text{deadband}(\omega_{ref} - \omega) - STAT \cdot (P - P_0)$$

The error enters an integrator with rate limits $[GRADMIN, GRADMAX]$ (pu/s) filtered through a ramp time $TGRAD$. The integrator output $x_I$ passes through a servo $TSM$.

Turbine characteristic with GOMP:

The turbine output is non-linearly mapped through a gain $GOMP$:

$$P_m = \min\!\left(\frac{x_I}{GOMP},\, 1\right) \cdot f(x_I)$$

where the limiter prevents over-power and $f$ is a piecewise-linear characteristic.

The steam-valve rate is held inside $[VFN,\, V0]$, then passes the valve actuator lag $TFV$, the reset lag $TRES$ and $GOMP$ to produce the final torque. $VFR$ overrides the rate during fast valving, a path the shipped model never takes: the code fixes its selector at 1 and leaves the fast-valving logic unwritten.

Parameters from Fortran source:

Index	Name	Description
1	STAT	Governor static characteristic selector
2	DEADB	Deadband half-width (pu)
3	DBON	Deadband onset (pu)
4	GRADMAX	Maximum load gradient (pu/s)
5	GRADMIN	Minimum load gradient / unloading rate (pu/s)
6	TGRAD	Ramp filter time constant (s)
7	TSM	Servo time constant (s)
8	V0	Maximum valve opening rate, upper limit on the steam-valve rate (pu/s)
9	VFN	Minimum valve rate, applied directly as the lower bound, so normally negative (pu/s)
10	TFV	Valve actuator time constant (s)
11	VFR	Valve rate limit (pu/s)
12	ALPHA	Integral gain
13	TRES	Reset time constant (s)
14	GOMP	Output power gain

Implementation details:

• nbxvar = 4, nbzvar = 8, nbdata = 14, nbaddpar = 1
• Additional: prm(15) = P0 (initialised from load-flow power)
• Observable: TM

Usage Example

RAMSES Data File

SYNC_MACH g1  g1  1. 1.  0.  0.   800. 760. 3. 0. 0.95
                    XT   0.15  1.1  0.25   0.2   0.7   *   0.2  0.1  6.0257  0.  5.00  0.05  *  0.1
              EXC GENERIC1   1.8991 -0.1  0.  1.  100. -1. -11  10.  70.  10.  20. 0.1  0.  4.
                                1     75.   15.    0.2    0.01     0.2    0.01    -0.1    0.1
              TOR GOVNUC  1.0  0.005  0.002  0.02  -0.02  10.0  5.0  1.0  1.0  0.50  0.10  1.0  20.0  1.0 ;
              !            STAT DEADB   DBON GRADMAX GRADMIN TGRAD TSM  V0  VFN   TFV   VFR ALPHA  TRES  GOMP

Notes

• Nuclear plants typically have slow load-following characteristics: GRADMAX is typically 0.005–0.02 pu/s.
• The DEADB is important to prevent hunting around the setpoint.
• GOMP scales the turbine output; set to 1.0 for standard normalisation.