1. FREQUENCY CONTROL DURING BLACK START OPERATIONS
The Isochronous Governor Control Generator and QSE Remote Constant Frequency Control
Sydney Niemeyer: NRG Energy

2. Introduction
Frequency Control During Black Start Operations is intended to provide basic dos and don’ts of frequency control during system recovery following a Black out. Review of Isochronous Governor Control of a Resource and Constant Frequency Control of an Island is included.

3. Objectives At the completion of this course of instruction you will:
Identify the importance of understanding the amount of Primary Frequency Control available during Black Start and Island grid operations.
Identify the amount of Primary Frequency Control available on an Island grid.

4. Objectives Continued: Identify the effects of cold load pick-up
Identify the importance of one Isochronous Governor Control Resource per island.
Identify the importance of having one QSE on Constant Frequency Control per island.

5. Definitions
Area Control Error (ACE): The instantaneous difference between a Balancing Authority’s net actual and scheduled interchange, taking into account the effects of Frequency Bias, correction for meter error, and Automatic Time Error Correction (ATEC), if operating in the ATEC mode. ATEC is only applicable to Balancing Authorities in the Western Interconnection.

6. Definitions Area Control Error (ACE): Continued.
Since ERCOT is not synchronously connected to any other Balancing Authority the net actual and scheduled interchange values are always zero.
ERCOT does not correct for meter error in the measurement of actual interchange.
ERCOT does not utilize ATEC.
QSE’s on Constant Frequency Control (Flat Frequency Control) implement the ACE calculation exactly as ERCOT.

7. Definitions
Automatic Generation Control (AGC): Equipment that automatically adjusts generation in a Balancing Authority Area from a central location to maintain the Balancing Authority’s interchange schedule plus Frequency Bias. AGC may also accommodate automatic inadvertent payback and time error correction.

8. Definitions
Black Start Resource – A generating unit(s) and its associated set of equipment which has the ability to be started without support from the System or is designed to remain energized without connection to the remainder of the System, with the ability to energize a bus, meeting the Transmission Operator’s restoration plan needs for real and reactive power capability, frequency and voltage control, and that has been included in the Transmission Operator’s restoration plan.

9. Definitions
Frequency Bias: A value, usually expressed in megawatts per 0.1 Hertz (MW/0.1 Hz), associated with a Balancing Authority Area that approximates the Balancing Authority Area’s response to Interconnection frequency error.
Frequency Bias Setting: A value, usually expressed in MW/0.1 Hz, set into a Balancing Authority ACE algorithm that allows the Balancing Authority to contribute its frequency response to the Interconnection.

10. Definitions
Frequency Bias Setting: (approved by NERC, not approved by FERC) A number, either fixed or variable, usually expressed in MW/0.1 Hz, included in a Balancing Authority’s Area Control Error equation to account for the Balancing Authority’s inverse Frequency Response contribution to the Interconnection, and discourage response withdrawal through secondary control systems.

11. Definitions
Droop governor: a governor that changes the electricity generated proportionally to the change in electrical frequency. The slope of this change represents the ratio of electricity generated change to the frequency change.
100% electricity change for a 5% change in frequency is 5% droop.

12. Definitions
Isochronous governor: 1) a governor that maintains the same speed in the mechanism controlled regardless of the load. 2) The frequency of the electricity generated is “Flat” or constant and there is zero generator droop.
RTU – Remote Terminal Unit

13. Content The Black Start Generator and Frequency Control
The next Start Generator and Frequency Control
Sources of Primary Frequency Control
Sources of Load Dampening
Island Frequency Control

14. Black Start Resource
Must operate with Isochronous governor in service.
As electrical load is connected to the Black Start resource the governor responds to control the prime mover to maintain frequency to the frequency reference of the governor, 60 Hz.

15. Isochronous Governor Controller
Turbine actual speed = 3600 rpm
2 pole generator = Hz
Comparator
Device
Increase Prime Mover if frequency is low, Decrease Prime Mover if frequency is high.
Reference input equal to Hz

16. Isochronous Generator Controls to Target Frequency
Load must remain within generator’s capability.
The Isochronous Governor Controller does the rest. 60 57 63
Generator
Frequency Hz

17. The “Grid”
Black Start
Black Start

18. Busses cleared except for Black Start plant.
Next Start
Black Start
Busses cleared except for Black Start plant.
Next Start
Black Start

19. Second Black Start unit running. Two islands.
Next Start
Black Start
Next Start
Second Black Start unit running. Two islands.
Black Start

20. Preparing to Start the Next Start units.
Black Start
Preparing to Start the Next Start units.
Next Start
Black Start

21. Next Start units on in the two islands.
Black Start
Next Start units on in the two islands.
Next Start
Black Start

22. Island 2
10 MW
20 MW Capacity
8 MW Output
300 MW Capacity
90 MW Output
Island 1
Black Start 1
Next Start D
10 MW
15 MW
House Load
Next Start 2
400 MW Capacity
12 MW Output
5 MW
Black Start A
60 MW Capacity
30 MW Output
Island 1:
420 MW Capacity
20 MW Load
Island 2:
360 MW Capacity
120 MW Load
100 MW

23. Island 1 Next Start 2 generator is operating near minimum load.
Unit is typically less stable.
Risk of over-heating steam turbine from too little steam flow.
Minimum flow is 2% to 5% of nameplate depending on manufacturer.
Increase Island load if possible.

24. Island 2
Should start next generator to balance load on generators. Increases reserves.
Consider minimum operating conditions on each generator added to the island.
Operating above minimum load on generator provides ability to place controls in AUTO at plant.
Improves Primary Frequency Response delivery.

25. Island 2 10 MW Island 1 20 MW Capacity 8 MW Output 300 MW Capacity
Black Start 1
Next Start D
10 MW
400 MW Capacity
70 MW Output
15 MW
House Load
Next Start 2
400 MW Capacity
12 MW Output
Island 2: Now with 3 generators on line. Prepare for Constant Frequency Control.
15 MW
Black Start A
60 MW Capacity
30 MW Output
Island 1:
420 MW Capacity
20 MW Load
Island 2:
760 MW Capacity
170 MW Load
100 MW
40 MW

26. Island Remote Constant Frequency Control
QSE should have MW telemetry from each generator connected.
QSE must have frequency telemetry from the island.
At least one generator must be capable of remote dispatch (AGC).
Black Start generator must be switched to “droop” governor control from isochronous control.

27. Preparation for Constant Frequency Mode
QSE of the Island generators will not be following ERCOT Base Points.
QSE will calculate Base Points for each controllable generator.
QSE will calculate Island Area Control Error (ACE) using Constant Frequency (Flat Frequency) mode.
Verify that Scheduled Frequency is set to Hz.

28. Determine Island Frequency Response
To calculate ACE of the island, the Frequency Response of the island must be estimated.
ACE = (HzActual – HzScheduled ) * -10 * Bias
Where Bias is the estimated Frequency Response of the island, a negative number.
Determine MW capacity of all generators connected to the island that have a working “droop” governor.

29. Determine Island Bias Sum the island MW generation capacity.
Divide the capacity by 30.
The result is the estimated frequency response of the island in –MW/0.1 Hz.
Capacity of frequency responsive generators = 760 MW.
760 MW/30 = 25.3 MW/0.1 Hz.
Bias setting should be -25 MW/0.1 Hz.

30. Bias Setting and Load Dampening
Synchronously connected loads provide some frequency response to the island.
Synchronous AC motors on fans, pumps etc.
Florescent lighting.
Under normal conditions on the ERCOT grid, the frequency response of load on the grid can be estimated by multiplying the load (MW) by to get its MW/0.1 Hz contribution.

31. Bias Setting and Load Dampening Continued
For a 30,000 MW load the frequency response provided by load dampening would be 30,000 * = 73.5 MW/0.1 Hz.
During very cold weather with ERCOT load above 42,000 MW, the multiplier will reduce to since resistive heating load is not frequency responsive.
During early stages of building an island, the load dampening contribution will be very small and can be ignored.

32. Know Your Generator Control System
Some QSE Generator Control Systems require the Bias value to be entered as a positive number. It is converted to a negative value within the ACE calculation.
It is simple to determine if you have Bias set correctly.
If frequency is below target, the ACE value should cause generation to increase output.
If frequency is above target, the ACE value should cause generator to decrease output.

33. Bias Setting Lower Better
Initially set Bias lower than calculated until several load pickups have been observed.
Cold Load Pickup will initially appear as 10 times the load increase but will decrease with time. It is better to under control (raise generation slowly) to avoid frequency oscillations as the cold load pickup will decay with time and aid frequency recovery to normal.

34. Cold Load Pick-up
When adding load remember that cold load pickup is 10 times the steady state load and takes up to 30 minutes to decay.
1 MW pick up looks like 10 MW and will cause frequency to drop to from 60 Hz with an island Bias of 25 MW/0.1 Hz.
3 MW pick up looks like 30 MW and will cause frequency to drop to Hz.

35. Frequency Control in Constant Frequency Mode
Will NOT be similar to having the Black Start Generator on Isochronous control.
Frequency movement will be much greater.
Frequency recovery to schedule will be dependent on the ramp rate of the generator(s) on AGC.
Sustained Primary Frequency Response from all generators connected is critical for stable frequency control.

36. Keep Operating Margin
The QSE should closely monitor operating margins on all the AGC generators.
If Up or Down margin gets low, manually adjust non-AGC generators to give AGC generators more room to operate.
When moving other generation, consider the ramp rate of the AGC generators to avoid excessive ramping demands.

37. Prepare for Tying Islands Together
Synchronize smaller island to the larger island. (Smaller in MW load.)
Before synchronization, determine MW capacity of incoming island that will not be on Constant Frequency Control.
Calculate new Bias Setting of combined area by adding capacity of frequency responsive generators to existing island.

38. Bias Setting For Two Islands Connected
Existing Island on Constant Frequency Mode capacity: 1260 MW.
Incoming Island on Isochronous governor control by the Black Start generator. Capacity 420 MW.
Combined capacity: 1680 MW.
Bias Setting: 1680/30 = -56 MW/0.1 Hz.
Be sure to include only generation capacity that is frequency responsive.

39. Preparing to synchronize Island 1 to Island 2.
10 MW
20 MW Capacity
8 MW Output
300 MW Capacity
70 MW Output
Island 1
Black Start 1
Next Start D
Sync Point
10 MW
400 MW Capacity
70 MW Output
15 MW
House Load
Next Start 2
500 MW Capacity
90 MW Output
400 MW Capacity
12 MW Output
Island 2
15 MW
Preparing to synchronize Island 1 to Island 2.
Black Start A
60 MW Capacity
30 MW Output
Island 1:
420 MW Capacity
20 MW Load
Island 2:
1260 MW Capacity
260 MW Load
100 MW
130 MW

40. Synchronizing Two Islands
In the smaller island, take the Isochronous Black Start generator out of Isochronous governor control and place it in droop mode.
At Sync point, observe island voltages and match appropriately.
Observe Sync scope and adjust generation in smaller island to achieve a slightly “fast” rotation of the scope. Close the breaker at the proper phase alignment.

41. Connecting Two Islands When Both are on Constant Frequency
The process is the same as the isochronous generator.
Take the smaller MW load island (incoming generation) off Constant Frequency mode.
Field operator at Sync location should have contact with QSE of the incoming island to direct generation up or down to achieve proper synchronization.
Only one QSE remains on Constant Frequency mode after synchronization.

42. 10 MW 20 MW Capacity 8 MW Output 300 MW Capacity 70 MW Output 1 Island
Black Start 1
Next Start D
Sync Point
10 MW
400 MW Capacity
70 MW Output
15 MW
House Load
Next Start 2
500 MW Capacity
90 MW Output
400 MW Capacity
12 MW Output
15 MW
Synchronized
Black Start A
60 MW Capacity
30 MW Output
Island:
1680 MW Capacity
280 MW Load
Bias Setting: -56 MW/0.1 Hz
100 MW
130 MW

43. After Connecting Islands
QSE that remains on Constant Frequency mode adjusts Bias Setting to account for the additional frequency responsive generation.
Communicates through ERCOT for adjustments in generation operated by the other QSE.
Close additional tie lines to strengthen island connections.

44. 10 MW 20 MW Capacity 8 MW Output 300 MW Capacity 70 MW Output 1 Island
Black Start 1
Next Start D
10 MW
400 MW Capacity
70 MW Output
15 MW
House Load
Next Start 2
500 MW Capacity
90 MW Output
400 MW Capacity
12 MW Output
15 MW
Synchronized
Black Start A
60 MW Capacity
30 MW Output
Island:
1680 MW Capacity
280 MW Load
Bias Setting: -56 MW/0.1 Hz
100 MW
130 MW

45. One Generator on Isochronous Governor Control per Island or
One QSE on Constant Frequency Control per Island
Only one boss

46. Two Isochronous Governor Controls Active on One Island
Each generator will control to a slightly different frequency.
The generator controlling to the higher frequency will increase output.
The generator controlling to the lower frequency will decrease output.

47. Isochronous Governor Controller
Small conversion errors can exist at several locations.
1. Resolution of actual frequency, turbine speed.
Turbine actual speed = 3600 rpm
2 pole generator = Hz
Comparator
Device
Increase Prime Mover if frequency low, Decrease Prime Mover if frequency high.
3. Resolution of the comparator circuitry/logic.
Reference input equal to Hz
2. Resolution of reference frequency, is it an analog signal or digital.

48. Gen B switched to Isochronous Control and controlling to 60.002 Hz.
Gen A operating at 20 MW output and on Isochronous Control. Controlling to Hz
Gen B switched to Isochronous Control and controlling to Hz.
Gen B operating at 15 MW output and on Droop Control.

49. Why Only One QSE on Constant Frequency Mode
Just like having two Isochronous governor control generators active on the same island, Constant Frequency mode will generally result in undesired actions.
The problem is that neither control system will measure the exact same value for the frequency.
Neither control system will measure the exact same value for the frequency reference.

50. QSE Constant Frequency Mode
QSE A on Constant Frequency Control
Island ACE = (HzActual – 60.00) * -10 * Bias
Island Frequency
Bias
ACE
RTU
RTU
Target Frequency
60.00 Hz
Gen 2 MW and/or AGC Telemetry
Gen 1 MW, Hz & AGC Telemetry

51. QSE AGC Control Loop QSE’s AGC Generator
Converts Digital Count to Engineering Units (Hz) and sends Control Signals to AGC Generator based on ACE. 4
Converts 13.8 KV to 120 VAC
Potential Transformer 1
QSE Generation Control System
Frequency Transducer
Converts 120 VAC to madc or vdc 2
Converts madc or vdc to a Digital Count and transmits to QSE when requested.
RTU
Data Request 3
Data Reply
Generator Control

52. Summary
The Isochronous Governor Controlled generator will manage frequency of the island.
Don’t ask it to do more than it is capable of doing.
One Isochronous generator per island.
One Constant Frequency QSE per island.
Consider Generator minimum operating level before connecting to the island.

53. References
NERC Glossary:

54. Questions ? ?

55. Initially during the first energization of an island grid, frequency control in Real Time will be managed by the ___________________.
ERCOT Load Frequency Control (LFC) system.
QSE on Constant Frequency Control.
Resource on Isochronous Governor Control.
Resource on Droop Governor Control.

56. When a QSE initially begins controlling the island grid and places its Control System on Constant Frequency Control, they should set their Bias in their ACE equation to ________.
699 MW/0.1 Hz, the present ERCOT Bias setting.
698 MW/0.1 Hz, 1% of ERCOT Forecast Peak Load.
Total MW Capacity of the island being controlled divided by 30.
Sum of the frequency responsive MW Capacity of the island being controlled divided by 30.

57. Cold load pick up will initially appear as _____ times the load increase but will decrease with time. 5 7 9 10

58. Before a QSE places its Control System on Constant Frequency Control and begins controlling island frequency it must have _____________________.
ERCOT Frequency and ability to control one Resource connected to the island on AGC.
QSE Control System frequency and ability to control one Resource connected to the island on AGC.
Frequency of the island and ability to control one Resource connected to the island on AGC.
Resource on Isochronous Governor Control and one Resource on AGC, frequency input not needed.

59. When synchronizing two islands where both islands have one Resource on Isochronous Governor Control, what is the correct procedure in synchronizing the two islands?
Take both units off Isochronous Governor Control after synchronization to maintain stability, and leave the largest Island on Isochronous Governor Control.
Take the unit in the smallest Island off Isochronous Governor Control and place in droop prior to synchronization and leave the largest Island on Isochronous Governor Control.
Take the unit in the largest Island off Isochronous Governor Control and place in droop prior to synchronization and leave the smallest Island on Isochronous Governor Control.