Keeping it up to Speed Off-Nominal Frequency Operations. CETAC 2018 San Ramon

Transcription

1 Keeping it up to Speed Off-Nominal Frequency Operations CETAC 2018 San Ramon 1

2 Welcome CETAC 2018 San Ramon Valley Conference Center General Class Information: Safety/Fire evacuation In event of emergency, do not call 911 from your phone. Instructors will call front desk and they will notify first responders. Restrooms: Breaks: Hourly Cell phones on silent or outside. 2

3 Introduction Charles Asaah Steve Collins Boris Frenkel TID OE/Trainer PG&E Trainer PG&E Trainer 3

4 Class Objectives Review applicable NERC & WECC standards & individual Company procedures Given multiple, varied, grid scenarios, students will: Identify & desribe the effects to the bulk electric system (BES) of operating in Off-Nominal frequency ranges. Identify the relationships between system frequency, transmission and generation resources and transient grid events. 4

5 Class Objectives Given multiple, varied, grid scenarios, students will: Identify automatic systems, thresholds and associated activities designed to respond to grid underfrequency events. Identify the similarities & differences between the WECC Coordinated Underfrequency Plan & the Southern Island Load Tripping Plan. Coordinate grid restoration from transient area wide underfrequency events in coordination with transmission neighbors via manual & automatic modes. 5

6 Class schedule Review applicable standards & procedures Instructional Review of frequency theory Simulation Exercises & Worksheet Breaks = 1/hour 6

7 Student Credit CEH provided 4.0 Operating Topics, 4.0 Emergency Operations, 2.0 Simulation, 1.0 Standards Must complete the following: Sign roster Active classroom participation Worksheet (all exercises) Class Evaluation 7

8 Applicable standards & procedures NERC WECC variance + Coordinated plans Individual company UFLS procedures 8

9 EOP 011.R1 NERC Standards Each Transmission Operator shall develop, maintain, and implement one or more Reliability Coordinator-reviewed Operating Plan(s) to mitigate operating Emergencies in its Transmission Operator Area. The Operating Plan(s) shall include the following, as applicable: 1.2. Processes to prepare for and mitigate Emergencies including: Provisions for operator-controlled manual Load shedding that minimizes the overlap with automatic Load shedding and are capable of being implemented in a timeframe adequate for mitigating the Emergency; and 9

10 NERC Standards PRC 006 WECC Regional Variance D.B.3 Each Planning Coordinator shall adopt a UFLS program, coordinated across the WECC Regional Entity area, including notification of and a schedule for implementation by UFLS entities within its area, that meets the following performance characteristics in simulations of underfrequency conditions resulting from an imbalance scenario, where an imbalance = [(load actual generation output) / (load)], of up to 25 percent within the identified island(s). 10

11 PRC 006.R9 NERC Standards Each UFLS entity shall provide automatic tripping of Load in accordance with the UFLS program design and schedule for implementation, including any Corrective Action Plan, as determined by its Planning Coordinator(s) in each Planning Coordinator area in which it owns assets. 11

12 PRC 024.R1 NERC Standards Each Generator Owner that has generator frequency protective relaying activated to trip its applicable generating unit(s) shall set its protective relaying such that the generator frequency protective relaying does not trip the applicable generating unit(s) within the no trip zone of PRC-024 Attachment 1, 12

13 PRC 024, Attachment 1 NERC Standards 13

14 PRC 024, Attachment 1 NERC Standards 14

15 How does my company (or the company that performs TO and/or BA functions for my company) meet these standards? MID OB-52 PG&E TD-1426 SDG&E EOP-5130 EOP-5130A (Load) EOP-5130B (Gen) SMUD PSE 112 TID Off-Nominal Frequency Load Shedding & Restoration Plan, Rev. 19 WAPA OP-14 ISO 4510C

16 Frequency Theory What does system frequency represent? How is it changed; either above or below nominal? What system elements impact frequency? How does off nominal frequency impact the system and/or equipment? 16

17 Frequency Fundamentals NERC video = 1/video/

18 Frequency Fundamentals *EPRI Power Systems Dynamic Tutorial 18

19 Frequency Fundamentals So what are the characteristics of normal frequency deviations? How does the system maintain this state of normal deviations? 19

20 Managing System Frequency Effective management of frequency and reducing the risk of possible cascading outage has two main parts: Steady State Operations = Maintain adequate reserve of un-loaded generation (each control area must maintain adequate reserves) Transient Operations = Implement and maintain an under frequency load shedding program 20

21 Frequency Deviations: Normal & Transient *EPRI Power Systems Dynamic Tutorial 21

22 Frequency Fundamentals So what are the characteristics of abnormal/off-nominal frequency deviations? What does the system and/or Operators do to respond to these abnormal deviations and return the system within limits? 22

23 System Response to Low Frequency What is the initial system equipment that responds to frequency deviations? Generators/Governors Stages of Generator/Governor Response 1. Electromagnetic Energy Storage 2. Inertial Stage 3. Governor Response Stage 4. AGC Stage *EPRI Power Systems Dynamic Tutorial 23

24 Stages of Generator Response Identify the points (A-D) of the frequency chart below; what is occurring on the system and the synchronized generation at these points? A. Pre-disturbance frequency B. Undershoot or spike frequency (i.e. the point where the frequency drop is arrested ) C. Frequency stabilization point (i.e. the point where the initial generator governor response settles ) D. Frequency returns to nominal 24

25 Stages of Generator Response 25

26 Is frequency the same everywhere? The magnitude of the frequency undershoot varies with the observer s location. The stabilized value is the same no matter where the location in the interconnected system. Why is this? 26

27 Stages of Generator Response 27

28 System Response to Low Frequency Stages of Generator Response 1. Electromagnetic Energy Storage 2. Inertial Stage *EPRI Power Systems Dynamic Tutorial 28

29 System Inertia Inertia is defined as the property of an object that resists a change to the object s current speed and direction. The inertia of a generator refers to the generator s resistance to changes in its speed of rotation. 29

30 System Response to Low Frequency Stages of Generator Governor Response 1. Electromagnetic Energy Storage 2. Inertial Stage 3. Governor Response Stage 4. AGC Stage *EPRI Power Systems Dynamic Tutorial 30

31 System Response to High Frequency How does the system respond when the frequency is high? 1. Overshoot governor response 2. Overspeed generator tripping *EPRI Power Systems Dynamic Tutorial 31

32 PRC 024, Attachment 1 NERC Standards 32

33 Frequency Control Governor control is often referred to as primary frequency control while AGC is referred to as secondary frequency control. What happens when governor control/ generator response is not sufficient to arrest the frequency decline? What additional tools/actions are in place to stabilize the system? 33

34 Frequency Control What happens when governor control/ generator response is not sufficient to arrest the frequency decline? What additional tools/actions are in place to stabilize the system? The system requires one or more additional automatic system responses to equalize load & generation within limits; i.e. UnderFrequency Load Shedding (UFLS). 34

35 Load/Frequency Relationship Rule of thumb = 1% change in frequency = 2% change in load. Non-motor load does not vary with frequency. Motor load most impacted by frequency change; 1% change in frequency = 3% change in load. *EPRI Power Systems Dynamic Tutorial 35

36 Under Frequency Load Shedding OK, so the frequency didn t drop much, so what's the big deal? Loss of Generators Intertie impacts (O/Ls or separation) Islands (that must rebalance) Partial/full blackout 36

37 Under Frequency Load Shedding UFLS has multiple advantages for the system Decreased load demand Generation remains on line Frequency stabilized or rising In short, UFLS acts as a safety net to prevent frequency from getting too low and causing loss of additional generators and eventual cascading outages. 37

38 UFLS Design Purpose The intent of UFLS is NOT to recover the frequency to 60 Hz but rather to ARREST or STOP the frequency decline. Once UFLS has operated, manual intervention by the system operators is likely required to restore the system frequency to a healthy state. 38

39 UFLS Design What type of load is shed using UFLS? Distribution load (usually) at the feeder level 39

40 Governor Control v. Governor Control + UFLS 40

41 Equipment Damage as a result of Frequency Deviations Damage can occur to the following equipment: Turbine Blading Due to vibration as a result of abnormal frequency oscillations Longer, low pressure blading is the most susceptible There is a cumulative hour limit for off-frequency operations Transformer cores Can become overexcited Impacted by the ratio of (system) voltage to frequency Protected by???? 41

42 Why Off-Nominal Frequency Operation is undesirable Intermediate Pressure Turbine Low pressure turbine where blading is most susceptible to damage during low frequency/shaft RPM operation. High Pressure Turbine Turbine Front Standard including Governor and Main Oil Pump 6 0 person

43 Why Off-Nominal frequency operation is undesirable Utilizing Off-Nominal under frequency load shedding or over-frequency generator tripping limits the exposure to over/under frequency conditions to generating, transmission, and distribution and customer facilities to protect against damage

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45 UFLS: A Brief History Existing Under Frequency Load Shedding Program is based on requirements set forth by WECC after the July 2, 3, and August 10, 1996 West Coast black out. At the time of the disturbances, UFLS systems were implemented at many utilities, but they were uncoordinated Some areas dropped more load than they should have, others dropped too little or none at all. This resulted in very large flow increases on some inter-ties and caused them to open. This can even be worse than having no UFLS. 45

46 WECC Uniform Off-Nominal Frequency Program Objectives In the event of a system-wide disturbance, the WECC Coordinated Plan is designed to: Maintain Interconnection integrity Prevent unbalanced load shedding, extreme voltage deviations, and equipment damage Limit system islanding Allow quicker restoration and interconnection.

47 WECC Uniform Off-Nominal Frequency Program Design The Plan is designed and simulated to address the following performance criteria Accounts for load/generation imbalances of up to 25% Sufficient load must be dropped to keep frequency within the continuous operating range of the generating units (59.5 Hz and 60.5 Hz). Minimum permissible dynamic frequency during a disturbance is 58 Hz. The maximum permissible dynamic frequency during a disturbance is 61.0 Hz.

48 WECC Uniform Off-Nominal Frequency Program Design Well, what about Distributed Generation (DG; i.e. renewables)? Is it set to operate during off nominal conditions? It depends

49 WECC Uniform Off-Nominal Frequency Program Design Well, what about Distributed Generation (DG)? DG can be activated by two different thresholds triggers depending upon it s initial design IEEE 2003 IEEE 2014 PRC-024 settings The most recent WECC studies have addressed a 20-25% Distributed Generation (DG) loss scenario (loss of ~21,000 MW of DG) IF ALL DG tripped prior to UFLS schemes activating, the system could only remain stable for < 15% generation loss

50 WECC Uniform Off-Nominal Frequency Components The Coordinated Plan includes (but is not limited to): Frequency set-points Size of corresponding load shedding blocks (percent of connected loads) Intentional and total tripping delays Generation protection Tie-tripping schemes Islanding schemes Automatic load restoration schemes Any other schemes that are part of or otherwise affect this Coordinated Plan

51 WECC Coordinated Off-Nominal Frequency Load Shedding Plan The plan consists of designed system response to multiple scenarios: 1. WECC Island 2. Northern Island and 3. Southern Island

52 WECC Off-Nominal Frequency Plan Phases The plan consists multiple automatic responses 1. Load Block Tripping 2. Load Restoration

53 WECC Off-Nominal Frequency Plan Phases The plan consists multiple automatic responses 1. Load Block Tripping 37.1% pro rata for every entity 8 total load blocks Trip at distribution level 5 or 6 high speed (6 cycle) starting at 59.3 or 59.1 Low speed (~30 seconds) stalling blocks

54 WECC Off-Nominal Coordinated Plan High Speed Load Blocks Load Shedding Percent of Customer Pickup Block Load Dropped (Hz.) 1 5.3% 59.1 Tripping Time Not > than 14 cycles 2 5.9% % % % 58.3 Total 31.1%

55 WECC Off-Nominal NWPP Plan High Speed Load Blocks Load Shedding Percent of Customer Pickup Block Load Dropped (Hz.) 1 5.6% 59.3 Tripping Time Not > than 14 cycles 2 5.6% % % % 58.6 Total 28.0%

56 WECC Off-Nominal Frequency Plan Automatic Load Shedding to correct Under Frequency Stalling Load Shedding Block Percent of Customer Load Dropped Pickup (Hz.) Tripping Delay 6 2.3% sec 7 1.7% sec 8 2.0% sec Total 6.0%

57 WECC Off-Nominal Frequency Plan Phases The plan consists multiple automatic responses 2. Load Restoration Blocks Manual, controlled restoration is the preferred method Automatic time based restoration (30 min) Frequency must be above If frequency is above nominal; restoration times are proportionate to frequency Limited load pickup no more than 2% every 5 minutes

58 WECC Off-Nominal Frequency Plan Load Automatically Restored from 59.1 Hz Block to Correct Frequency Overshoot Load Shedding Block Percent of Customer Load Picked-Up Pickup (Hz.) Tripping Delay 1 1.1% sec 1 1.7% sec 1 2.3% sec Total 5.1%

59 WECC Off-Nominal Frequency Plan Generation Tripping Requirements Under Frequency Limit (Hz.) Over Frequency Limit (Hz.) Tripping Delay > 59.4 < 60.6 Continuous Seconds Seconds Seconds.75 Seconds 57.0 >61.7 Instantaneous Systems that have generators that do not meet the tripping requirements in table 5A must automatically trip load, in addition to that required in table 2A to match the anticipated generation loss and at comparable frequency levels.

60 Exercise Working in groups of 2-3 & using student worksheet Complete UFLS Exercise scenarios Be prepared to discuss the Application Questions. 60

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62 Southern Island Load Trip Plan Southern Island Load Tripping Plan (LTP) is designed to trip loads at higher frequency levels than the standard underfrequency load-shedding plan in order to reduce the potential of generator tripping following system separation and thus the need for additional load shedding. The load-tripping plan needs to be sufficiently robust to work under varying system operating conditions (southern island import levels, load, and transfer conditions). Slide 62

63 Southern Island Load Trip Plan The LTP will reduce the likelihood of generator tripping and loss of tie lines by reducing the voltage and frequency swings. During the August 10, 1996 disturbance that separated the system into islands, 12,000 MW of load was lost in northern California and 16,000 MW of load was lost in the remainder of the southern island (Arizona, southern California, Nevada, New Mexico and northern Baja Mexico) Slide 63

64 Southern Island Load Trip Plan The LTP provides for load tripping to protect against the loss of the COI lines and system separation under high north to south transfers into the southern island. For COI loss, three equal levels (1200 MW each) of load tripping would be armed in the southern island, based on southern island import and stored energy levels. Slide 64

65 Southern Island Load Tripping Plan or LTP Load Shedding can be implemented by: 1. Direct Load Tripping (DLT) 2. High-Level Under-Frequency Load Shedding (HLUFLS) Can Operate at 59.6 or 59.5 Can be added to the overall load requirements for UFLS Block 1 Slide 65

66 LTP LTP Consists of 3 parts: Study results indicate a maximum of 3600 MW of DLT or HLUFLS need to be tripped under light load conditions and high imports into the southern island at to Hz. The total California load-tripping responsibility is approximately 2650 MW DLT or HLUFLS. The LTP recommends allocation of load-tripping responsibility totaling 950 MW DLT or HLUFLS to load control areas in the Desert Southwest with allocations based upon peak demand. Slide 66

67 Southern Island Load Trip Plan The California load tripping responsibility is divided evenly between northern (50%) and southern (50%) California and then apportioned out to the individual organizations based upon peak demand. Slide 67

68 Exercise Working in groups of 2-3 & using student worksheet Complete SILT Exercise scenarios Be prepared to discuss the Application Questions. 68

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70 Operator Actions During Under Frequency Events What action(s) should the Operator take during an UF event? 70

71 Operator Actions During Under Frequency Events Determine actual frequency Determine if source of frequency deviation is internal or external Check flow of inter-ties; Direction & magnitude of load Determine if overall system load has dropped Did any UFLS circuits operate? Determine if any RAS scenarios or actions occurred Did it operate as designed? If possible/time allows, Dispatch additional generation 71

72 Wrap Up Review applicable NERC & WECC standards & individual Company procedures Given multiple, varied, grid scenarios, students will: Identify & describe the effects to the bulk electric system (BES) of operating in Off-Nominal frequency range(s). Identify the relationships between system frequency, transmission and generation resources and transient grid events. 72

73 Wrap Up Given multiple, varied, grid scenarios, students will: Identify automatic systems, thresholds and associated activities designed to respond to grid underfrequency events. Identify the similarities & differences between the WECC Coordinated Underfrequency Plan & the Southern Island Load Tripping Plan. Coordinate grid restoration from transient area wide underfrequency events in coordination with transmission neighbors via manual & automatic modes. 73

74 74

75 Assessment 75

76 Course Credit Did you sign roster? Did you actively participate in class? Did you fill out a worksheet? Did you complete the assessment? Did you complete the course evaluation? 76