Methods for Establishing IROLs

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Suzan Elliott
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1 Methods for Establishing IROLs Informational Webinar NERC Methods for Establishing IROLs Task Force (MEITF) January 25, 2019

2 Logistics This is an informational webinar to describe the efforts of the NERC Methods for Establishing IROLs Task Force (MEITF) Multiple industry presenters who were deeply involved in the MEITF efforts The webinar will be recorded and posted on the NERC MEITF webpage All attendees are muted upon entry Please submit questions along the way via the Q&A feature of the WebEx meeting As time permits, presenters will address the submitted questions 2

3 MEITF Background NERC Project Establishing and Communicating SOLs Standards Drafting Team (FAC SDT) Attempted to create IROL-related requirements to balance specificity and flexibility Concerns raised by FERC staff FAC SDT reached impasse Methods for Establishing IROLs Task Force (MEITF) formed to support FAC SDT SDT moved forward with SOL-related requirements 3

4 MEITF Objectives Create technical guidance and reference material for methods for establishing IROLs Develop a framework for potential future FAC standards revisions related to IROLs (IROL Framework) Provide potential future revisions to NERC Glossary terms to provide clarity and consistency with standards requirements Provide clarity for reporting IROL Exceedances (NERC M8) 4

5 MEITF Deliverables Original IROL Framework (approved by NERC PC and OC in December 2017) Recommended Glossary Terms (approved by NERC PC and OC in December 2017) Guidance for IROL Exceedance Reporting (to NERC PAS) Reliability Guideline: Methods for Establishing IROLs (approved by NERC PC and OC September 2018) IROL Framework Assessment (approved by NERC PC and OC in September 2018) 5

6 NERC MEITF Membership Vic Howell Peak* Dean LaForest ISO-NE* Hari Singh Xcel Energy* Lee Taylor Southern Co.* Charles-Eric Langlois Hydro Quebec* Dan Woodfin ERCOT* Andrew Arana FPL Ryan Quint NERC* Kyle Thomas Dominion* Emanuel Bernabeu PJM Wayne Guttormson SaskPower Gary Keenan NWPP Gary Kobet TVA Durgesh Manjure MISO Nathan Schweighart TVA David Souder PJM John Stephens City Utilities of Springfield Eddy Lim FERC Hamody Hindi BPA * Denotes webinar speaker. 6

7 Proposed IROL-Related Definitions and IROL Framework 7

8 Proposed Definitions 8

9 Original IROL Framework (Framework A) Each Reliability Coordination shall include in its SOL Methodology a description of how the subsets of SOLs that qualify as IROLs are established. This methodology should, at a minimum: 1. Describe the analytical techniques used to study and determine Instability, System Instability, Uncontrolled Separation, and Cascading 2. Require that IROLs are established to prevent System Instability 3. Require that loss of load greater than 2000 MW caused by Instability, Uncontrolled Separation, or Cascading is unacceptable and warrants the establishment of an IROL 4. Establish a risk assessment process for determining which SOLs should be considered IROLs to prevent an unacceptable loss of load between 300 MW and 2000 MW due to Instability, Uncontrolled Separation, or Cascading. This risk assessment process shall, at a minimum, include considerations for: a. Amount of pre-contingency load shedding necessary b. Resulting impacts to neighboring Reliability Coordinator Areas c. Nature of the load (e.g., economics, criticality, geographic region, etc.) at risk d. Restoration plans and estimated time to restore the affected load at risk e. Risk of contingencies more severe than single contingency events 9

10 MEITF Efforts MEITF developed initial framework based on group consensus More rigid than existing framework in place Adds clarity to definitions and application in standards Provides some flexibility to RC for their specific system FERC Staff expressed concerns regarding framework Too flexible Does not align with Reliable Operation definition MEITF decided to do an assessment of their framework versus an alternative framework that was believed to be somewhat supported by FERC Staff 10

11 Alternative IROL Framework (Framework B) 11

12 Assessment Example 12

13 Assessment Example 13

Assessment Example IROL Established (Scenario #1) Framework B SOL Established (Scenario #2) Framework A Value Units Description Value Units Description 148 hrs Hours above load level that would

14 Assessment Example IROL Established (Scenario #1) Framework B SOL Established (Scenario #2) Framework A Value Units Description Value Units Description 148 hrs Hours above load level that would exceed IROL 3 hrs Hours to restore load following collapse 100 % Likelihood of load tripping 1.7 % Likelihood of load loss due to collapse 30 MW MW that must be shed to remain below IROL 160 MW MW that would be lost during collapse 4447 MWh Expected annual at-risk energy loss from enforcing IROL 8.2 MWh Expected annual at-risk energy loss due to exceeding SOL Conundrum: 4447 MWh (deterministically) vs. 8.2 MWh (probabilistically) 14

15 Reliability Guideline: Methods for Establishing IROLs 15

16 Principles for Defining IROLs An IROL is a limit, not a condition IROLs are a subset of SOLs, and both IROLs and SOLs exist IROLs address an elevated risk to BES reliability IROLs require pre-contingency load shedding to mitigate exceedance, if all other options have been exhausted; SOLs do not IROLs are generally established prior to real-time operation during off-line studies When unforeseen operating conditions are encountered, focus should be on returning to a secure operating state and not on establishing an IROL in real-time Either an SOL or an IROL can be the more restrictive operating limit If an IROL is less limiting than other SOLs, studies and engineering judgment should be used to identify where the IROL exists IROLs should be established in coordination with other activities including outage coordination Real-time tools may refine or update IROL limits How Operating Plans for SOLs are developed may affect the frequency and duration of any potential IROL exceedances IROLs have a mitigation time (Tv) and may require actions to prevent or mitigate an exceedance up to and including pre-contingency load shedding 16

17 IROL Construct Constraint: The set of limiting system elements that are monitored to manage the risk of system instability, cascading, and uncontrolled separation. Limit: The limiting value of the constraint to ensure that system instability, cascading, and uncontrolled separation do not occur if the critical contingency(ies) were to occur. 17

18 Process of Establishing IROLs 18

19 Time Frames of Establishing IROLs 19

20 Study Considerations Study assumptions* Demand level Generation dispatch High transfers and/or loop flows Facility outages Load model sensitivity Fault clearing time Contingency Event Selection Continuity of Performance Criteria *Study assumptions can add reliability margin to resulting limits established 20

21 Types of Operating Limits Facility Ratings System Voltage Limits Transient Stability Limits Frequency Stability Limits Voltage Stability Limits High Frequency and Control-Related Stability 21

22 Proxy Limits 22

23 Operating Limit Margin Operating Limit Margin: a value or range applied to a System Operating Limit 23

24 Classification of Power System Stability Adapted from IEEE/CIGRE

25 Instability Impact Considerations Amount (MW) of generation or load lost due to instability Resulting system conditions from loss of gen, load, or elements Number of tripped transmission elements or affected buses Impacted electrical and geographical area Margin to more widespread instability issues Criticality of the load being served System restoration time and blackstart considerations Impacts to neighboring TOPs or RCs 25

26 Rotor Angle Instability 26

27 Rotor Angle Instability 27

28 Small Signal Instability Oscillation in Actual System Oscillation in Stability Simulation 28

29 Voltage Instability Analysis 29

30 Voltage Instability 30

31 Voltage Instability Analysis 31

32 Soft Outage Approach Approach for ensuring that diverged powerflow is indicative of actual instability versus simulation numerical issues Engineering judgement needed to determine when soft outage applicable Divergent powerflow does not necessarily equate to unbounded cascading or system instability Is indicative that further analysis needed to determine extent of instability Entails gradual change in state (e.g., topology, statuses, etc.) Line impedance increase, generation ramp, reactive output steps, etc. Applies to instability and cascading analysis 32

33 Voltage Instability 33

34 Voltage Instability 34

35 Controls-Related and Other Types of Instability Stable Frequency Scan Unstable Frequency Scan Source: ERCOT 35

36 Using Real-Time Stability Tools Potential Benefits Timely execution Increasing tools capabilities More accurate assessment Effective support to Operation Plans Less conservative assumptions/margins Potential Challenges Complexity of instability assessment Computational limitations Tools simplifying assumptions Need for engineering judgment Database maintenance and management Sensitivity analysis 36

37 Uncontrolled Separation vs. Controlled Separation 37

38 Uncontrolled Separation vs. Controlled Separation Source: FPL 38

39 Cascading Analysis Bounded Cascading: 39 Cascading that stops after some number of elements have been removed from the system All elements are within pre-defined thresholds and no further successive tripping risks exist More common where higher impedance elements exist in a meshed lower impedance system Also common in load/gen pockets where cascading risk eliminated upon tripping of pocket Unbounded Cascading: Cascading that subsequently results in system instability The cascading does not reach a new steady-state; system enters truly dynamic, uncontrolled condition May consider number elements threshold as proxy for unbounded cascading

40 Cascading Analysis Series Cascading Parallel Cascading Source: TVA 40

41 Cascading Analysis Source: Dominion, PJM 41

42 Cascading Analysis Source: ISO-NE Cascading analysis needs to consider technically viable post-contingent flows where action can be taken. The time-based aspects of Facility Ratings should drive cascading threshold selection. 42

43 Cascading Analysis 43

44 Conclusions Technical reference material should be considered by ALL RCs RC SOL Methodologies should be improved with materials from guideline Guidance provided to SDT (or future SDT) on IROL Framework, for consideration in future SDT efforts to develop IROL-related requirements in FAC Standards Framework assessment of pros and cons regarding original and alternative IROL frameworks 44

45 Relevant Materials MEITF Webpage HERE Reliability Guideline: Methods for Establishing IROLs HERE IROL Framework Assessment HERE Includes Framework A and B Includes proposed Glossary definitions Questions? Send to Ryan Quint (ryan.quint@nerc.net). 45

46 46

Supporting Reference for Indentification of Interconnection Reliability Operating Limits

Supporting Reference for Indentification of Interconnection Reliability Operating Limits Purpose Planning Authorities (PAs), Transmission Planners (TPs), and Reliability Authorities (RAs) identify System Operating Limits (SOLs) via various planning and operating studies and real-time experience.