Automatic Generation Control

Automatic generation control (AGC) is a system for adjusting the power output of multiple generators at different power plants, in response to changes in the load. Since a power grid requires that generation and load closely balance moment by moment, frequent adjustments to the output of generators are necessary. The balance can be judged by measuring the system frequency; if it is increasing, more power is being generated than used, which causes all the machines in the system to accelerate. If the system frequency is decreasing, more load is on the system than the instantaneous generation can provide, which causes all generators to slow down.

1. AUTOMATIC GENERATION CONTROL Presented by: Birju Besra 1 RVS College of Engineering and Technology

2. OUTLINES : Automatic generation control An Introduction The need of Automatic Generation Control Reasons for limiting frequency deviations Automatic generation control (Block diagram) Automatic voltage regulator(AVR) Automatic load frequency control(ALFC) Exciter modelling Generator modeling Speed governing system Future work 2 RVS College of Engineering and Technology

3. In an electric power system,  automatic generation control (AGC)  is a system for adjusting the power output of multiple generators at different power plants, in response to changes in the load. Since a power grid requires that generation and load closely balance moment by moment, frequent adjustments to the output of generators are necessary. The balance can be judged by measuring the system frequency; if it is increasing, more power is being generated than used, which causes all the machines in the system to accelerate. If the system frequency is decreasing, more load is on the system than the instantaneous generation can provide, which causes all generators to slow down. AUTOMATIC GENERATION CONTROL 3 RVS College of Engineering and Technology

4. As our development has increased, there has been a higher demand of electrical power loads both on industrial and domestic scale. As the number increases, it is also imperative to manage load properly since a failure to do so results in frequency fluctuation and voltage drops. An effective regulatory strategy is available in the form of Automatic Voltage Regulator Systems (AVR ) and Automatic Load Frequency Control ( ALFC ) The main function of  ALFC system  is to assess and rectify the power and frequency while that of AVR system is to regulate voltage and reactive power. The Need of Automatic Generation Control 4 RVS College of Engineering and Technology

5. REASONS FOR LIMITING FREQUENCY DEVIATIONS There are few reasons as to why there should be strict limitations on frequency deviations and keeping the system frequency constant. They are as follows : The three phase a.c. motors running speed are directly proportional to the frequency. So the variation of system frequency will directly affect the motor performance . The blades of the steam turbine and the water turbines are designed to operate at a particular speed and the frequency variations will cause change in the speed. This will lead to excessive vibration and cause damage to the turbine blades . The frequency error may produce havoc in the digital storage and retrieval process. 5 RVS College of Engineering and Technology

6. AUTOMATIC GENERATION CONTROL (BLOCK DIAGRAM) 6 RVS College of Engineering and Technology

7. The exciter is the main component in the AVR loop. It delivers the DC power to the generator field. It must have adequate power capacity and sufficient speed of response. The basic role of the AVR is to provide constancy of the generator terminal voltage during normal and slow changes in the load. Automatic Voltage Regulator(AVR) 7 RVS College of Engineering and Technology

8. Exciter Modelling: Mathematical modelling of the exciter and its controls follows: and where is amplifier gain Laplace Transformation of these two equations yields and where is amplifier transfer function In reality the amplifier will have a delay that can be represented by a time constant and its transfer function will then be of the form 8 RVS College of Engineering and Technology

9. If and represent respectively the resistance and inductance of the exciter field we have for voltage equilibrium in the latter Measured across the main field the exciter produces armature volts per ampere of field current , that is, we have the proportionality Upon Laplace Transformation of the last two equations and elimination of we obtain the transfer function of the exciter where and The time constants and have values in the ranges 0.02-0.10 and 0.5-1.0 seconds respectively. 9 RVS College of Engineering and Technology

10. Linear model of the comparator-amplifier-exciter portion of AVR loop 10 RVS College of Engineering and Technology Amplifier Exciter Comparator

11. Generator Modeling: We need to close the loop in fig. by establishing the missing dynamic link between the field voltage and the generator terminal voltage equals the internal emf minus the voltage drop across the internal impedance it is clear that the relationship between and depends on the generator loading. The simplest possible relationship exists at low or zero loading in which case V equals approximately the internal emf . 11 RVS College of Engineering and Technology Amplifier Exciter Generator Sensor

12. where open circuit time constant rotor winding self inductance rotor winding resistance typically have values in the range 5-10 seconds 12 RVS College of Engineering and Technology

13. RVS College of Engineering and Technology 13 MATLAB Simlation of AVR Amplifier K A =10 T A =0.1 Exciter K e =1 T e =0.4 Generator K f =1 T do =0.2 Sensor K r =2 T r =0.05

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15. AUTOMATIC LOAD FREQUENCY CONTROL(ALFC) The basic role of ALFC is : T o maintain desired megawatt output of a generator unit matching with the changing load To assist in controlling the frequency of larger interconnection To keep the net interchange power between pool members at the predetermined value The ALFC loop will maintain control only during normal (small and slow) changes in load and frequency. It is typically unable to provide adequate control during emergency situations, when large megawatt imbalance occur. Then more drastic emergency control must be applied. 15 RVS College of Engineering and Technology

16. SPEED GOVERNI`NG SYSTEM 16 RVS College of Engineering and Technology

17. The system consists of the following components: Fly ball speed governor Hydraulic amplifier Linkage mechanism Speed changer I. Fly ball speed governor : This is the heart of the system which senses the change in speed frequency. As the speed increases the fly balls move outwards and the point B on linkage mechanism moves downwards. The reverse happens when the speed decreases 17 RVS College of Engineering and Technology

18. II.Hydraulic amplifier: It comprises a pilot valve and main piston arrangement. Low power level pilot valve movement is converted into high power level piston valve movement. This is necessary in order to open or close the steam valve against high pressure steam. III.Linkage mechanism: ABC is a rigid link pivoted at B and CDE is another rigid link pivoted at D. This link mechanism provides a movement to the control valve in proportion to change in speed. It also provides a feedback from the steam valve movement 18 RVS College of Engineering and Technology

19. IV. Speed changer: It provides a steady state power output setting for the turbine. Its downward movement opens the upper pilot valve so that more steam is admitted to the turbine under steady conditions. The e reverse happens for upward movement of speed changer 19 RVS College of Engineering and Technology

20. RVS College of Engineering and Technology 20 Speed Governer Turbine Generator Load Sensor Modeling of Automatic Load Frequency Control

21. RVS College of Engineering and Technology 21 MATLAB Simlation of ALFC Speed Governor K sg =1 T sg =0.2 Turbine K t =1 T t =0.5 Generator Load K ps =1 T ps =10 Sensor R=0.05

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23. THANK YOU 23 RVS College of Engineering and Technology