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Index Terms Automatic Generation Control ControlSystems Control Generation Power Operation.

I. I NTRODUCTION

HIS document provides the main characteristics of theAutomatic Generation Control (AGC), which is the one incharge to maintain the generation of the Caruachis units

within its operation limits satisfying the requirements of the National Power System.

In a interconnected system like the one of CVG EDELCAit is important to maintain the programmed interchange of active power, and that the frequency of the system staysconstant in a value of 60 Hertz. The changes in the frequencyof the power system occur because the system load variesrandomly, this unbalance between the generated active power and the load demand give as a result the variation of thefrequency, for such reason to eliminate this error it isnecessary a program like the Automatic Generation Control.1For understanding of this paper, the followings points have

been considered: Description of the Caruachi HydroelectricPower Plant, Caruachi Control Center System and finally to

present the relevant characteristics of the AGC.

D. J. Garcia is with the Department of Generation Control Center, CVGEDELCA, Guayana City, 8050 VENEZUELA (e-mail:dhgarcia@edelca.com.ve).

J. L. Loreto is with the Department of Generation Control Center, CVGEDELCA, Guayana City, 8050 VENEZUELA (e-mail:

jloreto@edelca.com.ve).

II. D ESCRIPTION OF THE CARUACHI HYDROELECTRIC POWER PLANT

The Caruachi hydroelectric power plant represents the third project developed by CVG EDELCA in the low Caron,oriented to fortify the social and productive sectors of thecountry through the generation of electrical energy. Theinfrastructure necessary to achieve these objectives consists of a power house with twelve (12) generating units, each one

with a capacity of generation of 180 MW for a total production of energy of 11,300 million kilowatts hours per year; which are transmitted by means of the 400 kV Caruachisubstation.

The configuration of the generation units is of twomachines by each transformer with a relation of transformation of 13.8/13.8/400 kV.

For the supervision and control of so significantcontribution of energy to the power system, the power planthas a computer control system that allows conducting the safeand reliable operations fortifying the national electrical

provision .In Fig. 1 is shown a panoramic view of the Caruachi

Hydroelectric Power Plant.

Fig. 1. Caruachi hydroelectric power plant.

III. D ESCRIPTION OF CARUACHI CONTROL CENTER SYSTEM

A. SCCC Master Station ConfigurationThe master station of the Caruachi Control Center System

Automatic Generation Control of the CaruachiHydroelectric Power Plant

D. J. Garcia, and J. L. Loreto

T

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DISTRIBUTED CONTROL

OPERATION CONSOLES TRAINING SYSTEM

HISTORIANSERVERS

CONFIGURATIONSERVER

WEBSERVER

ICCPSERVERS

PROCESS NETWORK

DATAPROCESSING

MAINTENANCESERVER

(SCCC) is an integrated system constituted by servers of high performance, workstations and programs which allow to makeall the functions of supervision and control of the CaruachiHydroelectric Power Plant, in addition it counts with aredundant process network (optical fiber) which allows tomaintain communication between the different servers. In Fig.2 is shown in a schematic way the configuration of theCaruachi Control Center System.

Fig. 2. SCCC Configuration.

1) Data Processing Server:They are the servers who are in charge to process all the

information coming from distributed control, that is to say,from all the control boards that contain all the information of the generation units, the switchyard and the Caruachi spillgates. Besides in these servers, the on line application

programs such as: the Automatic Generation Control (AGC),Automatic Voltage Control (AVC) and Automatic Spill gatesControl (SGC), run in real time.

2) Maintenance Servers:They are the Controcad servers in where the maintenance

jobs are made, such as, modifications to the data base of theentire system .

3) Historian Servers:They are the servers in charge of the storage of all the real

time data of the system that have been defined to be store inhistorical tables .

4) ICCP Servers:They are the servers in charge of the data interchange

between the SCCC and the control center of CVG EDELCA(SCCE) from the System Operations Center (COS). Thiscommunication is made through the communication protocolICCP (Inter Control Center Protocol).

5) Configuration Server:It is the server through which the entire system data base is

generated and loaded, additionally; it is the one that containsthe configuration of all the servers of the SCCC.

6) Training system:This server emulates the dynamic conditions of the power

system and the power plant and it is used for the training of the operators of the power plant before they go to operate thesystem in real time.

7) Operation consoles:They are workstations where the operators supervise and

control the Caruachi Hydroelectric Power Plant.

8) Web Server:It is the server that contains the documentation and

schematics of the system.

B. SCCC on line ApplicationsIn the master station of the SCCC there are integrated on

line application programs used by the operator of the power plant with the purpose of supervise and control the generationof the units, the voltage of the bars of 400 kV switchyard andthe spill gates of the Caruachi power plant. These programsare the Automatic Generation Control (AGC), AutomaticVoltage Control (AVC) and the Automatic Spill gates Control(SGC).

The AGC is the one that is in charge of automaticallyadjust the generation of the units of the Power Plant, with theintention of fulfilling the requirements of generation of CVGEDELCA. The AVC makes a real time dispatch of the reactive

power of the Power Plant and maintains the voltage in thegenerators and in the switchyard, its objective will be tomaintain the voltage in the 400 kV bars in the required levelwhile the balance of the load of reactive power of each unit ismaintain. Finally, the SGC is in charge to maintain thevolume of the river and the level the dam by means of

adjustments of the Spill gates.

IV. A UTOMATIC GENERATION CONTROL

A. DefinitionThe Automatic Generation Control (AGC) of the SCCC is

an application function, that controls the generation units belong to the Caruachi Hydroelectric Power Plant, in responseto frequency changes in the power system, deviations of timeor a combination of these and in addition to satisfy therequirements of active power that are received from theSystem Operations Center or those that are established by theoperator of the power plant.

B. Generation Control Error CalculationThe variable that determines when the power plant must

increase or diminish the generation, according to theregulation of the system, is the Generation Control Error (GCE); it represents the deviation of the total generation of the

power plant with respect to the desired total generation.

C. Automatic Generation Control Objectives

1) To vary the power output of the generators that is incontrol to reunite the requirements of active power of CVG

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EDELCA. The adjustment of the generation can be received from the System Operations Center, obtained from forecast values or manually introduced by the operator of the power

plant.

2) To maintain the system frequency as close as possible tothe reference frequency .

D. Control Modes

1) Active:In this mode the AGC collects data and automatically

builds the setpoint for the units that are in automatic mode andin addition the operator can send the setpoint to the close loopcontrols of active power of the units that are in the controlmode Base Load without Regulation and Base Load withRegulation.

2) Inactive:In this mode the AGC collects data but it does not transmit

any control to the close loop controls of active power of the

units.

E. Operation Level

1) Caruachi:The generation of active power of the power plant is

controlled from the control room of the power plant.

2) Dispatch:The generation of active power of the power plant is

controlled from the System Operations Center .

F. Processing Modes

1) Active Power:The requirements of generation of the power plant that will

be used by the AGC for the control of the active power of the power plant, are assigned manually by the operator of the power plant as a base value which previously is coordinatedwith the System Operations Center, additionally, they can bereceived from the System Operations Center through the ICCPlink between control centers or be obtained from a table of forecast values. In this mode the GCE is calculated as thedifference between the actual generation minus the desiredgeneration.

2) Frequency:In this case the requirements of generation of the power

plant are calculated by the AGC, but taking into account onlythe component from the frequency of the system (programmedminus actual) and the respective frequency polarizationconstant for the calculation of the GCE.

3) Time Error Correction:The requirements of generation of the power plant are

calculated taking into account the time deviation.

4) Active Power and Frequency:In this mode of control the AGC calculates the

requirements of generation of the power plant, or GCE, takinginto account for it the variation of active power (programmedminus actual) and the variation of frequency (programmedminus actual) and the respective frequency polarizationconstant.

5) Active Power, Frequency and Time Error Correction:The requirements of generation of the power plant are

calculated taking into account the variation from active power and the variation of frequency but now considering the timedeviation.

G. .Capture Mode of Active Power

1) Setpoint:In this mode the operator of the control room can introduce

the setpoint of active power, which will be processed by theAGC to control power plant active power; this setpoint alsocan be received from the System Operations Center.

2) Forecast:In this mode the setpoint of active power can be read from

a table of programmed values or forecast values.

In Fig. 3, Operation of the AGC, can be seen the fields of the Control Modes, Operation Levels, Processing Modesamong other relevant parameters of the AGC of the SCCC.

Fig. 3. Operation of the AGC.

H .Control Modes of the Generation Units

1) Automatic:The Unit participates completely to satisfy the variations of

active power generation of the power plant.

2) Base load without regulation:The unit does not participate within the regulation of the

system, to satisfy the variations of the power plant generation,remaining with a fixed generation established by the operator.

3) Base load with regulation:

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VIII. B IOGRAPHIES

Dhilegdys Garcia was born in Bolivar Venezuela, onSeptember 11, 1972. She Graduated of ElectricalEngineer at Antonio Jos de Sucre University(UNEXPO) on 1996.

Since 1998, is assigned as Supervisory andControl Systems Maintenance Engineer on CVGEdelca.

Jos Loreto was born in Valle de la PascuaVenezuela, on July 27, 1972. He Graduated of Electrical Engineer at Antonio Jos de SucreUniversity (UNEXPO) on 1996.

Since 1997, is assigned as Supervisory andControl Systems Maintenance Engineer on CVGEdelca.