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Governor and AGC Control of System Frequency TRE Technical Workshop March 31, 2009

Governor and AGC Control of System Frequency TRE Technical Workshop March 31, 2009. Bob Green Garland Power and Light. Two generators equipped with governors having output feedback. Schematic of a governor with output feedback. Response of governor with output feedback.

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Governor and AGC Control of System Frequency TRE Technical Workshop March 31, 2009

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  1. Governor and AGC Controlof System FrequencyTRE Technical WorkshopMarch 31, 2009 Bob Green Garland Power and Light

  2. Two generators equipped withgovernors having output feedback

  3. Schematic of a governor with output feedback

  4. Response of governor with output feedback

  5. Steady-state speed characteristic (droop) curve

  6. Calculation of steady-state speed characteristic R(per unit), the slope of the “droop” curve, is defined as f(p.u.)/ P(p.u.), where f(p.u.)= f(HZ) / 60.0,and P(p.u.)= P(MW) / Unit Capacity.For a 600 MW unit that has a governor response of 20 MW for a frequency excursion that settles out at 59.9 HZ, R=f(p.u.) / P(p.u.) = (0.1/60)/(20/600)=0.05 or 5% droop.Once the droop is known, the MW response to frequency deviation can be determined by (P/f)=(1/R), or P=(1/R) X f.For the 600 MW unit with 5% droop, (P/600)=(1/0.05) X (f/60), or P=200MW/HZ

  7. So, how do governors with the steady-state speed characteristic interact when there are multiple generators in a power system? What determines the steady state system frequency after a load is added to the system?

  8. Multiple Generator Governor Response Consider an isolated power system with three generators on-line and operating at 60HZ. The load is 360 MW and the generator outputs for units #1, #2 and #3 are 80MW, 120MW and 160MW, respectively. A load of 21MW (P) is added. What frequency does the system settle at? How much does each unit pick-up (MW)? Since R(p.u.)=( f(HZ)/60)/( P(MW)/Capacity), then (P/f)=(1/R) X Capacity/60).

  9. Three generators serving 360MW

  10. Three generators serving 367MW

  11. Three generators serving 374MW

  12. Three generators serving 381MW

  13. The system frequency reaches steady-state at a value that causes the sum of the on-line generator output MW to be equal to the system load MW.With this type of governor, when the system load increases, the system frequency decreases and visa versa.How do we control frequency to 60HZ, no matter what the load is?

  14. Power system equipped for supplemental control

  15. Addition of a speed changer

  16. Steady-state speed characteristic with speed changer

  17. Power output as a function of frequency

  18. How does the addition of the speed changer to the governor facilitate the control of frequency?Hint: The system frequency reaches steady-state at a value that causes the sum of the on-line generator output MW to be equal to the system load MW.

  19. From a central site, you increase or decrease the 60HZ set-points until the sum of the 60HZ set-points is equal to the system load. Then the frequency will stabilize at 60HZ.This form of supplemental control is called Automatic Generation Control (AGC) and more specifically, Load Frequency Control (LFC).

  20. Load of 367MW and 60HZ SPs increased by 7 MW

  21. Load as a function of frequency (load damping)

  22. Governor and load characteristic curve intersection

  23. Illustration of typical governor dead band

  24. Generation oscillations at the dead band frequency

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