1. NPRR833 Workshop: Contingency Processing in CRR, DAM and SCED
Shams Siddiqi, Ph.D.
Crescent Power, Inc.
(512)
QMWG Meeting
June 27, 2017

2. How are Contingencies created?
Network Operations Modeling Expectations for TSPs, REs, and QSEs:
"Single element contingencies will be programmatically generated and appended to each CIM model."
"The typical modeling criteria for contingency definitions are straightforward; contingencies are modeled breaker-to-breaker between autotransformers, non-radial AC transmission lines, or between a generator and its high-side breaker.“
“ERCOT will submit NOMCRs and model double contingencies in NMMS after consulting with the owners of the equipment in the double contingencies.”
Thus, programmatically generated single contingencies do not include radial lines and, logically, double contingencies also do not result in islanding in the normal status of Network Operations Model
Therefore, all islanding contingencies are inadvertent and due to change in network topology, i.e. transmission element outages
Solution (Option 1 & 2): Run contingency generation tool with current network model (that includes outages) and eliminate contingencies from approved Contingency List that are not in list of contingencies from this run
– no radial/islanding contingency would be modeled in SCED/DAM/CRR
June 27, 2017

3. ERCOT Handling of SPS/RAS
SCED: According to ERCOT, there is pre-positioning of generation for Generators outaged due to activation of SPS/RAS, i.e. EMS does pass to SCED any post-SPS activation overloaded constraints (if Generator backed down or tripped by SPS, pickup factors used to model loss of generation in constraint passed to SCED?)
DAM: No SPS/RAS related constraints are considered in DAM
CRR: No SPS/RAS related constraints are considered in CRR
Generation contingency (G-1) and transmission contingency (T-1) that results in islanding (outage) of generation are similar to SPS
NERC requirements for G-1 are met using Ancillary Services (RRS); T-1 with islanding could take out G-X, with X>>1; there is no requirement to be G-X secure
Option 4: Treat G-1 and T-1 with islanding same as SPS/RAS in DAM/CRR: do not consider in DAM/CRR (G-1 already not considered in DAM and CRR)
June 27, 2017

4. G-1 Problem: Irresolvable Conflict
Does NERC require dispatch to be G-1 secure for post-contingency transmission overload or is the NERC requirement to ensure ERCOT has enough Ancillary Services (like RRS) to meet G-1?
In load pocket, T-1 may require generator G to run full out with high prices (SF ~ -1) whereas G-1 of the same G may require that the G be backed down (SF ~ 0) - how is this resolved? What if there are no other alternatives to resolve these conflicting constraints? Shadow price cap for the G-1 constraint is same as line shadow price cap – this can result in G being backed down with very high price for constraint violation at the "connectivity node“
G-1s exist where the resource node is also outaged – exactly like T-1 with islanding. Then, prices are set using pickup SF or Generation Distribution Factors (GDFs) – large uplifts and oversold CRRs
Unit-specific (not resource node) settlement and pricing required to model G-1 in DAM/CRR with different prices for units at same bus
Solution: Consider G-1 evaluation in EMS but not modeled in SCED
June 27, 2017

5. Decision Points G-1 not modeled in CRR and DAM but is modeled in SCED
Optimization Shift Factor (SF) for G in G-1 different from Settlement SF
May lead to oversold CRRs, uplift and discrepancy between EOC and Base Point
However, modeling G-1 in CRR/DAM raises many issues – not recommended
Consider evaluating in EMS but no constraints in SCED, DAM and CRR
Since T-1 with islanding is unintended, adjust contingency list
Run contingency generation tool with current network model (that includes outages) and eliminate contingencies from approved Contingency List that are not in list of contingencies from this run
No change to CRR and DAM engine required – PTP issue is automatically resolved
Implementation cost impact should be minimal compared to alternative
Avoids Unnecessary cost to system (consumers) through inefficient dispatch to enforce unintended constraints and cost to implement unintended constraints
If unintended T-1 with islanding and G-1 kept, then decide between
(A) Modified ERCOT proposal of modeling such contingencies in CRR/DAM with Generation Distribution Factors (GDF) based on AGC resource headroom – requires ERCOT to post GDFs and market to model these contingencies
(B) Treat similar to G-1; i.e. do not model in CRR/DAM but model in SCED – no change to CRR/DAM engines required but change contingency processing tool
June 27, 2017

6. G-1 Modeling and Settlement
G-1 not modeled in CRR and DAM but modeled in SCED with prices set using “connectivity node” SF – not optimization SF
Potential uplift and gaming opportunities exist
Min 10*G1 + 20*G2 + 50*G3 ST: a) G1+G2+G3 = 100; b) G2+0.5*G1 <= 40
G1=80, G2=0, G3=20, SPa=50, SPb =-80, LMPg1=$10, LMP2=-$30, LMP3=$50
However, ERCOT will settle G1 at “connectivity node” price, i.e. LMP1=$50
Congestion rent = 100*50-80*50-20*50 = $0
CRR payments = 40*(50-(-30))+200*(50-50) = $3,200
Uplift = $3,200 x
June 27, 2017

7. T-1 with Islanding same G1
T-1 with Islanding of the same G1 has exactly the same equations as G-1 in this example but G1 settled using Optimization SF (GDF)
Min 10*G1 + 20*G2 + 50*G3 ST: a) G1+G2+G3 = 100; b) G2+0.5*G1 <= 40
G1=80, G2=0, G3=20, SPa=50, SPb =-80, LMP1=$10, LMP2=-$30, LMP3=$50
Congestion rent = 100*50-80*10-20*50 = $3,200
If modeled the same in DAM and CRR using identical GDFs:
CRR payments = 40*(50-(-30)) or 80*(50-10) = $3,200
Uplift will be from differences in GDFs x
June 27, 2017

8. Why not use GDFs for G-1?
Using GDFs to set prices under G-1 introduces many complexities:
Settlement and prices would have to be at Unit level – not resource node level
Multiple generators at same resource node could have different prices
Min 10*G1+15*G1’+20*G2+50*G3
ST: a) G1+G1’+G2+G3 = 100; b) G2+0.5*G1 <= 40 c) G2+0.5*G1’ <=40
G1=80, G1’=10, G2=0, G3=10, SPa=50, SPb=-80, SPc=0
LMPg1=$10, LMPg1’=$50, LMP2=-$30, LMP3=$50
CRRs would be from units: Congestion rent = 100*50-80*10-20*50 = $3,200
CRR payments = 40*(50-(-30)) or 80*(50-10) + 80*(50-50) = $3,200
G1’=10MW at $15/MWh
June 27, 2017

9. Issues with Islanding Contingencies
The pricing and dispatch outcome from T-1 with islanding is quite unpredictable, depends on QSE behavior and can be manipulated:
If there were another unit G1' similarly connected in a separate node (even the same node for G-1 contingencies) owned by the same QSE as G1, then if the QSE commits both G1 and G1' with exactly the same total generation, there is no congestion and prices are $10/MWh everywhere. By committing only one of those units or keeping G1' at LSL of say 10MW, the QSE gets paid $50/MWh for the 10MW at G1' and $40/MW for each CRR from Node 1-3. This is much more profitable than getting $10/MWh for all its generation and $0 for its CRRs. Thus prices throughout the market are impacted by how this QSE decides to commit and dispatch its units and it's perfectly reasonable for the QSE to commit only G1 since Load is low.
June 27, 2017

10. Islanding Options: Pros & Cons
Eliminate Unintended Islanding Contingencies
Pros:
Contingency modeled similarly in CRR, DAM and SCED
Minimal cost to implement: rerun programmatic contingency generation
Cons:
None – islanding contingencies should not exist to begin with
Modified ERCOT approach:
Expensive - between $325k and $425k
Unnecessary cost to system (consumers) through Inefficient dispatch to enforce an unintended G-X (X>>1 in some cases when only G-1 required) constraint and cost to implement
Extensive changes and testing in CRR and DAM engines required
Electrically similar nodes may have significantly different prices – restrictions on activities in electrically similar nodes may mitigate some manipulation potential
GDFs need to be posted and these new type of contingencies need to be modeled by stakeholders to forecast congestion
June 27, 2017

11. Islanding Options: Pros & Cons
Treat Similar to G-1 approach (if G-1 is still modeled in SCED):
Pros:
Consistent treatment for exactly same outcomes
Expensive change to CRR/DAM engine not required – only contingency screen
No need for GDF posting and modeling by market for forecasting congestion
Cons:
Similar to G-1 – likely to result in larger uplift
June 27, 2017

12. Option 1: Eliminate Inadvertent Islanding
Contingency effect
SCED
DAM
CRR
#1 Outages branches
If violations, constraints developed
Same as SCED
#2 Outages branches and load
Eliminate any inadvertent radial and islanding contingencies
#3 Outages branches, load, generation, and resource node
#4 Outages unit
Evaluate in EMS for possible mitigation plan; no constraint sent to SCED
Contingency not considered (no change proposed)
June 27, 2017

13. Option 2: Remove Island; Keep G-1
Contingency effect
SCED
DAM
CRR
#1 Outages branches
If violations, constraints developed
Same as SCED
#2 Outages branches and load
Eliminate any inadvertent radial and islanding contingencies
#3 Outages branches, load, generation, and resource node
#4 Outages unit
Pickup used – i.e. use GDFs in optimization but settle using “connectivity node” prices if available; otherwise GDF-based prices
Contingency not considered (no change proposed)
June 27, 2017

14. Option 3: ERCOT Proposal
Contingency effect
SCED
DAM
CRR
#1 Outages branches
If violations, constraints developed
Same as SCED
#2 Outages branches and load
Implement load rollover if available, otherwise generators back down. If violations, constraints developed – i.e. contingency LDFs changed based on distributing load to rollover bus or to all other load zone buses
Implement load rollover scheme if available, if not load is redistributed in load zone. If there are violations, constraints developed – i.e. contingency LDFs changed based on distributing load to rollover bus or to all other load zone buses
Same as DAM, except doesn’t implement load rollover. – i.e. contingency LDFs changed based on distributing PTP source/sink bids at load zone to all other load zone buses
#3 Outages branches, load, generation, and resource node
Pickup used for outaged generator, constraint developed – i.e. LDFs changed in contingency as #2 but use GDFs for distributing outaged generation
Pickup used for generator and for transactions at resource node. PTP will be included in the pickup. – i.e. LDFs changed as #2 but use GDFs for generation and bids/offers at resource node
Similar to DAM – i.e. LDFs changed as #2 but use GDFs for PTP source/since at resource node
#4 Outages unit
Pickup used – i.e. use GDFs in optimization but settle using “connectivity node” prices if available; otherwise use GDF-based prices
Contingency not considered (no change proposed)
June 27, 2017

15. Option 4: Treat Islanding Like G-1
Contingency effect
SCED
DAM
CRR
#1 Outages branches
If violations, constraints developed
Same as SCED
#2 Outages branches and load
Implement load rollover if available, otherwise generators back down. If violations, constraints developed – i.e. contingency LDFs changed based on distributing load to rollover bus or to all other load zone buses
Contingency not considered
#3 Outages branches, load, generation, and resource node
Pickup used for outaged generator, constraint developed – i.e. LDFs changed in contingency as #2 but use GDFs for distributing outaged generation
#4 Outages unit
Pickup used – i.e. use GDFs in optimization but settle using “connectivity node” prices if available; otherwise GDF-based prices
Contingency not considered (no change proposed)
June 27, 2017