Examples of Current Paradigm vs. Future Proposed Paradigm

Transcription

1 Examples of Current Paradigm vs. Future Proposed Paradigm 10/30/2013 POTF Meeting Webinar Created by Dede Subakti (CAISO), Bert Peters (APS), Vic Howell & Brett Wangen (WECC RC) Presented by Dede Subakti

2 Current Path SOL Paradigm Operating limits and scheduling limits are combined into a single parameter used in real-time operations the historical Operational Transfer Capability (OTC). Transfer Capability for WECC Paths = SOL; i.e., TTC = Path SOL. Example: o Path 66 (COI) has SOL = 4800 MW o Path 66 (COI) has TTC = 4800 MW 2

3 3 Proposed Alternate Paradigm 1. OTC/Path SOL concept retired 2. Paths have TTC as defined by NERC 3. SOLs are simply BES Facility Ratings and voltage limits that are not to be exceeded in both the pre- and post-contingency state. SOLs could also be stability limit that should not be exceeded in precontingency state*. 4. TTC is separate and distinct from SOLs (though overlap may occur for stability limits). TTC is not the SOL itself; rather, TTC respects SOLs. 5. Commercial considerations are upheld, but they do not determine the SOL; rather commercial considerations respect SOLs. 6. Transfer Capability/TTC and SOLs/IROLs work together to ensure operating reliability. Note:* stability limit is a contingency-based SOL. It is a proxy limit that is intended to protect the system against the adverse impacts of a pre-identified Contingency. It already includes a contingency notion in it. Protecting for contingency-based SOL proxy limit for post-contingency state is N-1-1 situation. As such, RTCA indication of a post-contingency exceedance of a contingency-based SOL does not generally require mitigating action

4 Examples The following slides present examples and compare the current paradigm with the new paradigm Example 1: Thermally Limited Path Example 2: Voltage Limited Path Example 3: Voltage Stability Limited Path Example 4: Transient Stability Limited Path 4

5 Example 1: Thermally Limited Path Path 66 - COI Flow Direction Summer 2013 OSS study shows: Northern CA Hydro COI SOL/TTC 60% 4800 MW 70% 4800 MW 80% 4680 MW 90% 4615 MW 100% 4373 MW 5

6 Example 1: Thermally Limited Path Path 66 - COI With hydro at 60% and 70%, COI is limited by Path Rating No SOL is exceeded and transfer analysis is stopped at 4800 MW With hydro at 80%, COI is limited to 4680 MW by the N-1 post contingency loading in Round Mt-Table Mt #1 for loss of #2 6

7 Lets examine the 4680 MW limit (What does it mean?) This means, In the OSS summer 2013 study case: with hydro at 80% with load level at the summer 2013 case with load distribution modeled in the case with gen dispatch modeled in the case According to the seasonal study, when COI = 4680 MW, the N-1 post-contingency loading in Round Mt Table Mt #1 for loss of #2 is right at 99.9~%. 7

8 In current Paradigm: All Line In Service If hydro is expected at 80%, then: Path 66 (COI) TTC will be set to 4680 MW The COI TTC is shared between BANC and CAISO according to its contract Path 66 (COI) SOL is set to 4680 MW All congestion management is done with regards to the 4680 MW limit 8

9 In current Paradigm: Forced Outage Hydro is running at 80% Path 66 (COI) TTC has been set to 4680 MW Path 66 (COI) SOL has been set to 4680 MW Table Mountain-Tesla 500kV line is forced out. Procedure limit is used and COI is set to a new limit of 3100 MW Operator curtailed tags and move COI down to 3100 MW 9 COI TTC is then set to 3100 MW; COI SOL is then set to 3100 MW; congestion management done with regards to 3100 MW

10 Lets examine the 3100 MW limit (What does it mean?) This means: in some study case: with hydro at 80% or 90% (depending study methodology) with load level in the case with load distribution modeled in the case with gen dispatch modeled in the case When COI = 3100 MW, then the N-0 pre contingency loading in TableMt-VacaDixon is right at 99.9~% of normal rating (there is no other SOL exceedance for N-1 or N-2; pre-ctg is more limiting) 10

11 11 Proposed Alternate Paradigm 1. Study to determine TTC still needs to be done 2. COI has TTC as defined by NERC 3. The TTC is as followed Northern CA Hydro COI TTC 60% 4800 MW 70% 4800 MW 80% 4680 MW 90% 4615 MW 100% 4373 MW 4. Contract allocation between BANC/WASN and CAISO still the same No change up to this point

12 Proposed Alternate Paradigm 5. COI does not have SOL 6. For this example, SOLs are simply BES Facility Ratings that are not to be exceeded in both the pre- and post-contingency state: Facility SOL Normal Emergency Round Mountain Table Mountain 500 kv line # Amp 3280 Amp Round Mountain Table Mountain 500 kv line # Amp 3280 Amp Table Mountain Vaca-Dixon 500kV line 2200 Amp 3280 Amp etc. etc 12 SOL is exceeded when: Real Time flow (in SCADA) is observed to be above its normal limit Real Time tools (such as RTCA) show N-1 flow is observed to be above its emergency limit

13 In Proposed Paradigm: All Line In Service So, if hydro is expected at 80%, then: Path 66 (COI) TTC will be set to 4680 MW o The COI TTC is shared between BANC and CAISO according to its contract o No change in TTC process Path 66 (COI) does not have SOL 13 System Operator will monitor: o Real Time flow (in SCADA) and ensure that real time flow in each of the transmission facility is below its normal limit o Real Time tools that calculate N-1 (or N-2) post-contingency flow and ensure that post-contingency flow in each of the facility is below its emergency limit All congestion management is done with regards to the real time flow and N-1 (or N-2) post contingency flow (as calculated by Real Time tools)

14 14 In Proposed Paradigm: All Line In Service What happens if COI flow is around 4680 MW? Note: All congestion management is done with regards to the real time flow and N-1 (or N-2) post contingency flow as calculated by RT tools Scenario 1: If COI is flowing at 4750 MW (above 4680 MW) and the RT tool shows that N-1 post contingency flow in Round Mountain-Table Mountain #1 for loss of #2 is still at 3200 A (below 3280 A), and no other N-0 or N-1 exceedance is observed, that means no SOL is exceeded Scenario 2: If COI is flowing at 4650 MW (below 4680 MW) and the RT tool shows that that N-1 post ctg flow in Round Mountain-Table Mountain #1 for loss of #2 is at 3300 A (above 3280 A) and there is no automatic action to resolve the thermal overload, then that means SOL is being exceeded in Post-Contingency. Operator is expected to do congestion management pre-contingency

15 In Proposed Paradigm: Forced Outage Hydro is running at 80% Path 66 (COI) TTC has been set to 4680 MW Path 66 (COI) SOL has no SOL Table Mountain-Tesla 500kV line is forced out. 15 Expected operator actions is that System Operator will monitor: o Real Time flow and ensure that real time flow is below or moving below its normal limit within the given facility rating (e.g. 30 min thermal rating, 4 hour thermal rating, etc..) o Be prepared for the next N-1 contingency by monitoring Real Time tools and ensure that N-1 post-contingency flow is below its emergency limit (as calculated by RT tools) These are the two goals that: 1. Engineering support staff will establish prevention/mitigation plans for prior to real-time, and 2. System Operators will focus on in real-time

16 In Proposed Paradigm: Forced Outage In achieving these two goals, the System Operator may: o Utilize Procedure limit and establish COI TTC to a new limit of 3100 MW o Operator curtailed tags, move generations and move COI flow down to 3100 MW Note: Based on study result, when COI = 3100 MW, then: The N-0 pre contingency loading in TableMt-VacaDixon is right at 99.9~% of normal rating There is no other SOL exceedance for N-1 or N-2; 16 But: The SOL is no longer exceeded when TableMt-VacaDixon is below its 2200 Amps limit with no other SOL exceedance for N-1 or N-2 COI TTC of 3100 MW is no longer relevant for use in measuring SOL exceedance because COI does not have SOL

17 Example 2: Voltage Limited Path Path XYZ Summer 2013 seasonal study shows Path XYZ is limited to 3250 MW because of voltage limitation 17

18 In current Paradigm: All Line In Service Scheduling and TTC of Path XYZ is set to 3250 MW Path XYZ has SOL of 3250 MW All monitoring and congestion management is performed utilizing the 3250 MW limit 18

19 Let s Examine the 3250 MW limit (What does it mean?) This means, In the OSS Summer 2013 study case: with load level at the summer 2013 case (1-in-10 summer peak case) with load distribution modeled in the case with gen dispatch modeled in the case When Path XYZ=3250 MW, then the N-1 post contingency loss of Line 4, voltage at Bus 1 = 218 kv 19

20 In current Paradigm: Forced Outage Line 3 is forced out of service Path XYZ TTC and SOL is now set to the procedure limit of 2050 MW due to post contingency voltage at Bus 1 for the next loss of Line 1 Operator moves to 2050 MW 20

21 Let s Examine the 2050 MW limit (What does it mean?) 21 This means, In the OSS Summer 2013 study case: with load level at the summer 2013 case (1-in-10 summer peak case) with load distribution modeled in the case with gen dispatch modeled in the case With Line 3 out; When Path XYZ=2050 MW, then the N-1 contingency loss of Line 1, Post contingency voltage at Bus 1=218 kv

22 In Proposed Paradigm: All Line In Service 22 Path XYZ will continue to have TTC of 3250 MW o No change in TTC process Path XYZ does not have SOL Bus 1 will have SOL of 218kV o 218 kv is the Normal and Emergency Voltage Limit of Bus 1 (maybe due to the requirement imposed by load served at Bus 1) System Operator will monitor: o Real Time flow and voltage and ensure that real time flow and voltage is acceptable o Real Time tools to calculate N-1 (or N-2) post-contingency flow and post contingency voltage and ensure that post-contingency flow and voltage is acceptable (flow is below its emergency limit and voltage is within its emergency limit) All congestion management is done with regards to the real time flow and voltage and N-1 (or N-2) post contingency flow and voltage (as calculated by Real Time tools)

23 In Proposed Paradigm: All Line In Service Scheduling and TTC of Path XYZ is set to 3250 MW Path XYZ has no SOL All monitoring and congestion management is performed utilizing the 218 kv limit of Bus 1 o o If Path XYZ is at 3300 MW (above 3250 MW) and RT tool show that postcontingency voltage of Bus 1 is still at 220kV (above 218 kv low emergency limit) - and no other pre- and post-contingency unacceptable condition; then there is no SOL being exceeded no congestion management is needed If Path XYZ is at 3200 MW (below 3250 MW) and RT tool shows that postcontingency voltage of Bus 1 is at 217kV (below 218kV low emergency limit), then SOL is being exceeded and congestion management is needed 23

24 In Proposed Paradigm: Forced Outage When Line 3 is forced out, the expected operator actions is that System Operator will monitor: o Real Time flow and voltage and ensure that real time flow and voltage is acceptable o Real Time tools to calculate N-1 (or N-2) post-contingency flow and post contingency voltage and ensure that post-contingency flow and voltage is acceptable (flow is below its emergency limit and voltage is within its emergency limit) These are the two goals that: 1. Engineering support staff will establish prevention/mitigation plans for prior to real-time, and 2. System Operators will focus on in real-time 24

25 In Proposed Paradigm: Forced Outage In achieving these two goals, the System Operator may: o Utilize Procedure limit for Line 3 outage and establish Path XYZ TTC to a new limit of 2050 MW o Operator curtailed tags and move flow down to 2050 MW Note: Based on summer season study result, when Path XYZ = 2050 MW, then: The N-1 post contingency voltage in Bus 1 for loss of Line 1 is right at 218 kv There is no other SOL exceedance for N-1 But: The SOL is no longer exceeded when the calculated post-contingency voltage in Bus 1 for the next N-1 loss of Line 1 meets its 218 kv criteria The Path XYZ TTC of 2050 MW is no longer relevant for use in measuring SOL exceedance because Path XYZ does not have SOL 25

26 Example 3: Voltage Stability Limited Path Summer 2013 seasonal study shows that Path 99 is limited to 15,000 MW because of voltage stability concern 26

27 In current Paradigm: All Line In Service Scheduling and TTC of Path 99 is set to 15,000 MW Path 99 has SOL of 15,000 MW All monitoring and congestion management is performed utilizing the 15,000 MW limit 27

28 Let s Examine the 15,000 MW limit (What does it mean?) 28 This means, In the OSS Summer 2013 study case: with load level at the summer 2013 case (1-in-10 summer peak case) with load distribution modeled in the case with gen dispatch modeled in the case When Path 99 > 15,750 MW, then the N-1 post contingency loss of Line 3, voltage collapse (WECC requires 5% margin for N-1)

29 In Proposed Paradigm: All Line In Service 29 Path 99 will continue to have TTC of 15,000 MW o No change in TTC process Path 99 will still have pre-contingency SOL. The SOL could be 15,000 MW o But: No change here either. SOL could be re-calculated utilizing real time tool o If TOP and TSP agree, TTC can be re-calculated utilizing real time tool in hourly basis System Operator will monitor: o Real Time flow and voltage and ensure that real time flow and voltage is acceptable. Same for post-contingency. o If TOP/RC has Real Time tools to calculate voltage stability limit (or can perform real time study), then real time voltage stability limit could be utilized for Path 99

30 In Proposed Paradigm: Forced Outage When Line 3 is forced out, the expected operator actions is that System Operator will monitor: o Real Time flow and voltage and ensure that real time flow and voltage is acceptable o Real Time tools to calculate N-1 (or N-2) post-contingency flow and post contingency voltage and ensure that post-contingency flow and voltage is acceptable (flow is below its emergency limit and voltage is within its emergency limit) Real Time tools to monitor for N-1 (or N-2) unsolved contingencies which may be indicative of post-contingency voltage collapse o If TOP/RC has Real Time tools (or real time studies) to calculate voltage stability limit, then real time tools could be utilized 30 These are the goals that: 1. Engineering support staff will establish prevention/mitigation plans for prior to real-time, and 2. System Operators will focus on in real-time

31 In Proposed Paradigm: Forced Outage In achieving these goals, the System Operator may: o Utilize Procedure limit for Line 3 outage and establish Path 99 TTC to a new limit of 13,000 MW o Path 99 SOL could be set to 13,000 MW o Operator curtailed tags and move flow down to 13,000 MW But: o If TOP/RC has Real Time tools (or can do real time studies) to calculate voltage stability limit, then real time tools could be utilized to establish new SOL for Path 99 o If TOP and TSP agree, TTC can be re-calculated utilizing real time tool in hourly basis 31

32 Example 4: Transient Stability Limited Path 32 The same similar approach with Voltage Stability Limited Path Path will continue to have TTC o No change in TTC process Path will still have pre-contingency SOL. The SOL could be based on procedure limit or it could be recalculated utilizing real time tool or studies o If TOP and TSP agree, TTC can be re-calculated utilizing real time tool in hourly basis System Operator will monitor: o Real Time flow and voltage and ensure that real time flow and voltage is acceptable. Same for post-contingency. o If TOP/RC has Real Time tools to calculate transient stability limit, then real time transient stability limit could be utilized (same with real time studies)

33 What if a path has both thermal and voltage stability limitation Study shows the following: 33 o When Flow in Path ABC = 3000 MW, the N-1 loss of Line 3 could overload Line 1: Line 1 and Line 3 both have 700 MVA normal rating and 900 MVA emergency rating Here the thermally limited TTC for Path ABC = 3000 MW o When Flow in Path ABC > 3255 MW, the N-1 Loss of Line 3 could cause a voltage collapse WECC requires 5% margin Voltage Stability limited TTC for Path ABC = 3100 MW

34 What if a path has both thermal and voltage stability limitation In Summary: o Thermally Limited TTC for Path ABC = 3000 MW o Voltage Stability Limited TTC for Path ABC = 3100 MW o The posted TTC in accordance to NERC MOD Reliability Standards need to respect all operating criteria; o TTC posted = 3000 MW 34

35 What about the SOLs What happens in Real Time? o For Thermal Limitation:, SOLs are simply BES Facility Ratings that are not to be exceeded in both the pre- and post-contingency state: Line 1 and Line 3 both have 700 MVA normal limit and 900 MVA emergency limit o For Voltage Stability: Path ABC will still have pre-contingency SOL. The SOL could be based on seasonal study/procedure study (which leads to SOL = 3100 MW) Operator will be monitoring Real Time Tools 35

36 What happens if Path ABC flow is around 3000 MW? Scenario 1: If Path ABC is flowing at 3050 MW (above 3000 MW) and the RT tool shows that N-1 post contingency flow in Line 1 for the N-1 loss of Line 3 is still at 850 MVA (below 900 MVA), and no other N-0 or N-1 exceedance is observed with acceptable N-0 and N-1 voltage, that means no SOL is exceeded Scenario 2: If Path ABC is flowing at 2950 MW (below 3000 MW) and the RT tool shows that that N-1 post contingency flow in Line 1 for the N-1 loss of Line 3 is at 910 MVA (above 900 MVA) and there is no automatic action to relief the thermal overload, then that means SOL is being exceeded in Post- Contingency. Scenario 3: If Path ABC is flowing at 3250 MW (above 3000 MW and above 3100) and the RT tool shows that N-1 post contingency flow in Line 1 for the N-1 loss of Line 3 is still at 890 MVA (below 900 MVA), but there is no real time study performed (or the actual RT tool show N-1 loss of line 3 shows divergence), then voltage stability based SOL on Path ABC is exceeded. 36 Scenario 4: If Path ABC is flowing at 3300 MW (above 3000 MW and above 3100) and the RT tool shows that N-1 post contingency flow in Line 1 for the N-1 loss of Line 3 is still at 895 MVA (below 900 MVA), and the RT Voltage Stability Tool/ RT studies shows voltage stability limit of 3500 MW, with RTCA shows acceptable N-1 voltage; then no SOL is exceeded.

37 Summary 1. Path has TTC 2. Path does not have SOL 3. SOLs are simply BES Facility Ratings and voltage limits that are not to be exceeded in both the pre- and post-contingency state. 4. SOLs could also be stability limit that should not be exceeded in precontingency state. 5. SOLs do rely on real-time tools and information If real time tools are unavailable, the transmission system should be operated to the study-based SOLs (which is often documented in procedures) 6. New paradigm do not require System Operator to Chase TTC if real-time tools shows that no SOL is being exceeded 7. When there is relatively small difference between thermal-based TTC and stability based TTC, the TOP is expected to operate to the most limiting condition that meets both criteria. 37

38 Questions?