Unit 4 Automatic Generation Control

Subject-Power System Operation Control

1. DEPARTMENT OF ELECTRICAL ENGINEERING JSPMS BHIVARABAI SAWANT INSTITUTE OF TECHNOLOGY AND RESEARCH , WAGHOLI, PUNE A.Y. 2020-21 (SEM-I) Class: B.E. Subject: Power System Operation Control Unit No-4 Automatic Generation and Control Prepared by Prof. S. D. Gadekar [email protected] Mob. No-9130827661

2. Content Introduction Concept of Automatic Generation and Control (AGC) Block Diagram of AGC Turbine Speed Governing System Complete block diagram representation of load frequency control of an isolated power system Free Governor Operation Numerical on Free Governor Operation Dynamics Response Proportional Plus Integral Control Automatic Voltage Control Two area load frequency control

3. Introduction     F For Steady operation or to keep frequency of supply constant ( F=50 Hz). If If    

4. Introduction Continue       For Steady operation the voltages at all buses must be constant (Voltage at Bus=Rated Value). ) Induced Emf E is called Excitation of Generator and it depends on field current and Power Factor of Generator.           Power Factor

5. Introduction In modern power system both active power and reactive power demands are never steady and they continuously changes. The mechanical power input must be continuously regulated to match the active power demand, failing which the machine speed will vary with consequent change in frequency. The permissible maximum change in power frequency in power frequency is 0.5 Hz. The excitation of generators must be continuously regulated to match the reactive power demand with reactive generation otherwise the voltages at various buses may go beyond the prescribed limit.  

6. Block diagram of Automatic Generation Control Turbine Generator Steam Valve Controller Frequency Sensor and Comparator Excitation Controller + - Voltage Sensor Comparator V F           Steam Steam Valve V, F

7. Control Area Turbine Generator   Steam Steam Valve Turbine Generator   Steam Steam Valve Turbine Generator   Steam Steam Valve Constant V, F Steam Valve Controller Frequency Sensor and Comparator   F

8. Control Area- All generators in an knit electric area constitute a coherent group so that all the generators speed up and slow down together maintaining their relative power angles. Such an area is called as control area.

9. Turbine Speed Governing System- Lower Raise Speed Changer Setting Fly Ball Speed Governor High Pressure Oil A B C D Pilot Valve Pilot Valve Direction of Positive Movement E Steam Out Turbine Steam In L1 L2 L3 L4 Hydraulic Amplifier

10. Turbine Speed Governing System- Fly B all S peed Governor- It sense the change in speed. As the speed increases the fly balls move outwards and the point b on linkage mechanism moves downwards. Hydraulic Amplifier- It comprises a pilot valve and main piston valve movement. Low power level pilot valve movement is converted in to high power level piston valve movement. Linkage Mechanism- ABC and CDE are two rigid links pivoted at B and D. This link mechanism provides a movement to the control valve in proportion to change in speed. Speed Changer- It provides a steady state power output setting for the turbine. Its downward motion opens the upper pilot valve, so that more steam is admitted to the turbine under steady conditions.

11. Complete block diagram representation of load frequency control of an isolated power system- Model of Speed Governing System Turbine Model Generator Load Model

12. Model of Speed Governing System- Let the point A on the linkage mechanism be moved downwards by a small amount . It is a command which causes the turbine power output to change. Where is the commanded increase in power.   The Command Signal )   The pilot valve moves upwards The high pressure oil flows on to the top of the main piston moving it downwards The Steam Valve opening increases The turbine generator speed increases i. e frequency goes up.

13. Model of Speed Governing System-   W h ere ,         (S)     + _

14. 2. Turbine Model-   LP Stage HP Stage Reheater (S)   (S)     (S)   (S)  

15. 2. Generator Load Model- The increment in power input to the generator load system is, Where is the incremental turbine power output and is the load increment . The increment in power input to the system is accounted for, Rate of increase of stored kinetic energy in the generator rotor. The loads sensitive to change in speed such as motor are changes.   Turbine Generator + -         V, F

16. 2. Generator Load Model-   W h ere , power system       (S)   + _  

17. Complete block diagram representation of load frequency control of an isolated power system-       (S)     + _   (S)   (S)     (S)   + _   Model of Speed Governing System Turbine Model Generator Load Model  

18. Complete block diagram representation of load frequency control of an isolated power system-         + _   (S)     (S)   + _     Consider the speed Changer has fixed settings and load demand changes. This operation is known as free governor operation. Sudden change in load demand by an amount (For Unit Step Input Function) is given as,  

19. Continue…. A B   +         -

20. Continue …               At steady state ,   and  

21. Continue …   This equation gives the steady state changes in frequency caused by changes in load demand. Frequency in Percentage Percentage Load Droop Characteristic 100% 50%  

22. Continue … Consider now the steady effect of changing speed changer setting with load demand remaining fixed   A B   +     -   If the speed changer setting is changed by , while the load demand changes by , the steady frequency change is   )  

23. Numerical-1 A 100 MVA Synchronous generator operates on full load at a frequency of 50 Hz. The load is suddenly reduced to 50 Mw. Due to time lag in governor system the steam valve begins to close after 0.4 seconds. Determine the change in frequency that occurs in this time. (H=5 kWs /kVA of generator capacity) H*Rating of Machine in kVA   Solution -------            

24. Numerical-2 Two Generators rated 200 MW and 400 MW are operating in parallel. The droop characteristics of their governors are 4% and 5%, respectively from no load to full load. Assuming that the generators are operating at 50 Hz at no load, how would a load of 600 MW be shared between them? What will be the system frequency at this load? Assume free governor operation. Repeat the problem if both governor s have a droop of 4%.   Solution -------               G1-200 MW G2-400 MW LOAD 6 00 MW

25. Numerical-2 Two Generators rated 200 MW and 400 MW are operating in parallel. The droop characteristics of their governors are 4% and 5%, respectively from no load to full load. Assuming that the generators are operating at 50 Hz at no load, how would a load of 600 MW be shared between them? What will be the system frequency at this load? Assume free governor operation. Repeat the problem if both governors have a droop of 4%.   Solution -------      

26. Numerical-3 A 100 MVA, 50 Hz generator is operating at no load at 3000 RPM. The load of 25 MW is suddenly applied to the machine. Due to inertia the valve does not open immediately but after 0.5 seconds. Inertia constant of generator is 4.5 MW-Seconds per MVA. Find frequency deviation before the valve opens to meet the load demand. Assume no change in load due to change in frequency. H*Rating of Machine in MVA   Solution -------            

27. Numerical-3 A 100 MVA, 50 Hz generator is operating at no load at 3000 RPM. The load of 25 MW is suddenly applied to the machine. Due to inertia the valve does not open immediately but after 0.5 seconds. Inertia constant of generator is 4.5 MW-Seconds per MVA. Find frequency deviation before the valve opens to meet the load demand. Assume no change in load due to change in frequency. Solution -------      

28. Numerical-4 A 100 MVA, 50 Hz generator is operating at rated speed. The load of 50 MW is suddenly applied to the machine. Due to inertia the valve does not open immediately but after 0.5 seconds. Inertia constant of generator is 5 kW-Seconds per kVA. Find frequency deviation before the valve opens to meet the load demand. Assume no change in load due to change in frequency. H*Rating of Machine in MVA   Solution -------            

29. Numerical-4 Solution -------     A 100 MVA, 50 Hz generator is operating at rated speed. The load of 50 MW is suddenly applied to the machine. Due to inertia the valve does not open immediately but after 0.5 seconds. Inertia constant of generator is 5 kW-Seconds per kVA. Find frequency deviation before the valve opens to meet the load demand. Assume no change in load due to change in frequency.  

30. Dynamic Response It is the change infrequency as a function of the time for a step change in load.     To obtain the dynamic response the above third order equation is required to approximate as first order as  

31. =         Take the inverse Laplace of above equation,  

33. Proportional Plus Integral Control- In a dynamic response we studied that there is a steady state drop in frequency of 0.029 Hz from no load to full load. System frequency specifications are rather stringent and therefore, so much change in frequency cannot be tolerated. In fact, it is expected that the steady change in frequency will be zero. While steady state frequency can be brought back to the scheduled value by adjusting speed changer setting, the system could undergo intolerable dynamic frequency changes with changes in load. So a signal from f is fed through an integrator to the speed changer setting.  

34.           1   + - + - The system now modifies to a proportional plus integral controller, which gives zero steady state error.

37. Automatic Voltage Control- It generally consists of main exciter which excites the alternator field to control the output voltage. The exciter field is automatically controlled through error The error is suitably amplified through voltage and power amplifiers.  

38. G Generator Field PT Load DC + -   Error Amplifier SCR Power Amplifier Stabilizing Transformer               Exciter Field

39. The Main components are, Potential Transformer-It gives sample of terminal voltage . Differencing Device-It gives the actuating error, Error Amplifier-It modulates and amplifies the error signal. SCR Power Amplifier and Exciter Field-It provides the necessary power amplification to the signal for controlling the exciter field. Alternator-Its field is excited by the main exciter voltage Stabilizing Transformer-  

40. Two Area Load Frequency Control- An extended power system can be divided into a number of load frequency control areas interconnected by means of tie lines. Such operation is called a pool operation. The basic principle of a pool operation in the normal steady provides Interconnected area share their reserve power to handle anticipated load peaks and unanticipated generator outages. Absorption of own load change by each area. Control Area 1 Control Area 2 Tie Line

41.         + _   (S)     1 (S)   + _             + _   (S)     (S)   + _     -a12   _ _

42. Turbine Speed Governing System- Lower Raise Speed Changer Setting Fly Ball Speed Governor High Pressure Oil A B C D Pilot Valve Direction of Positive Movement E Steam Out Turbine Steam In L1 L2 L3 L4 Hydraulic Amplifier Pilot Valve Pilot Valve

43. Turbine Speed Governing System- Lower Raise Speed Changer Setting Fly Ball Speed Governor High Pressure Oil A B C D Direction of Positive Movement E Steam Out Turbine Steam In L1 L2 L3 L4 Hydraulic Amplifier Pilot Valve Pilot Valve