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MISO Investigation Report on the Level 5 TLR Event Rockdale 345/138kV Transformer #2 for the outage of Paddock 345/138kV Transformer

Flowgate 3014 February 20, 2002

Report issued: April 2, 2002

This report is submitted in accordance with the NERC Transmission Loading Relief (TLR) Investigation Procedure for the TLR event that occurred on Flowgate 3014 on February 20, 2002. Flowgate 3014 is an American Transmission Company (ATCo) Flowgate in the Alliant Energy East (ALTE) Control Area. The duration of TLR Level 5a was approximately four hours. There was no curtailment of firm transmission service as a result of this TLR. Generation resources were acquired by ATCo and redispatched in order to mitigate impacts on the flowgate allow all affecting firm point-to-point transactions to continue to flow. Generation resources were also acquired by both ATCo and Commonwealth Edison (ComEd) in order to meet their respective Network Native Load (NNL) Service relief amounts - as specified by the Interchange Distribution Calculator (IDC). The NERC TLR Log is included as Appendix A. 1. Description of purpose/cause of hold/curtailment Flowgate 3014, an OTDF Flowgate, consists of the following elements. Monitored Facility: Rockdale 345/138kV Transformer #2 Contingent Facility: Paddock 345/138kV Transformer On Wednesday February 20, 2002 a variety of scheduled outages both internal and external to the Midwest ISO contributed to increase loading on Flowgate 3014. Contingency analysis determined that an overload of the Rockdale 345/138kV Transformer #2 would occur during the contingency outage of the Paddock 345/138kV T21 Transformer. NERC TLR had been issued at a level of 3a and increased to a level 4 and ultimately a 5a during the day. Outages that contributed to the necessity of a TLR level 5 included Columbia Unit 2, the Columbia-Rockdale 345 kV line, the Nelson-Electric Jct. 345 kV line (CE), and the Zion-Silver Lake 345 kV line (CE). 2. Facility/Flowgate limitations and flow at the time the TLR was initiated The short-term thermal limit of Flowgate 3014 (Rockdale 345/138kV Tr #2 for Paddock 345/138 Tr) was 336MVA. An ATCo Operating Guide was in place at the time that allowed the operating limit of the flowgate to be raised to 385MVA. Analysis conducted by the MISO and ATCo showed that the LODF (percentage of flow on the contingent facility Paddock 345/138kV T21 Transformer transferring onto the Rockdale 345/138kV Transformer #2) for Flowgate 3014 was 28.4% on this day (30.5% was indicated in the NERC IDC). The Flowgate was in TLR level 4 from 0754 CST until 1534 CST. During this time, there were no non-firm scheduled transactions flowing with 5% or greater impact on the flowgate. In lieu of going to a TLR level 5A, ATCo elected to redispatch sufficient generation to allow all firm point-to-point transactions to continue flowing and to sufficiently meet all NNL responsibilities

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as indicated by the IDC. The companies with NNL responsibilities on the flowgate as indicated by the IDC included Alliant East (ALTE), Madison Gas & Electric (MGE) and Commonwealth Edison (ComEd). Shortly after 1500 CST, ATCo elected not to continue redispatching generation to reduce ComEd’s NNL responsibility on the flowgate, but rather to only mitigate its own NNL responsibility as well as all firm point-to-point transactions on the flowgate. As a result, a TLR 5a was issued at 1534 CST effective at 1600 CST and remained in effect until 1928 CST. During this time, no firm point-to-point transactions were curtailed. ATCo redispatched generation per the TLR 5 curtailment list to meet relief requirements for all- firm transactions, ALTE NNL, and MGE NNL impacting the flowgate. At 2000 CST, a TLR 3A went into effect on flowgate 3014. The 100MW generation redispatch contract that had been set up by ATCo with ALTE’s Christiana Unit remained in effect until 2200 CST, though the MISO Reliability Authority did not require it after 2000CST. The generation redispatch contract set up by ComEd with ALTE’s Christiana Unit remained in effect until 2300 CST, though the MISO Reliability Authority did not require it after 2000CST. Non-firm transactions were permitted to reallocate and reload via Level 3a as of 2100 CST although there were no such schedules available to reload at that time. The chart below compares the calculated post-contingent loading on Flowgate 3014 to the short-term thermal limit (with the Operating Guide in place) throughout the course of the event.

Rockdale XFMR Flow and Post-contingent Flow (2/20/02 CST)

0

50

100

150

200

250

300

350

400

450

000

0:00

010

0:00

020

0:00

030

0:00

040

0:00

050

0:00

060

0:00

070

0:00

080

0:00

090

0:00

100

0:00

110

0:00

120

0:00

130

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140

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0:00

Rockdale XFMR 2 Flow

Post-Contingent Flow

OSL

TLR 4

TLR 5aTLR 4

TLR 3a

TLR 0

From the graph, it can be seen that the post-contingent loading on Flowgate 3014 exceeded its short-term limit for approximately 13 minutes before ATCo re-dispatch took effect in TLR 4.

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The loading remained near the Operating Guide enhanced limit throughout the day until approximately 1900 CST. Once the loading appeared to stabilize below the Flowgates OSL, the TLR level was reduced from a 5a to a TLR level 4. Eventually a TLR 3a and was issued and the event concluded with a TLR 0 at 22:20 CST. The IDC was unavailable from approximately 05:45 to 07:50 CST during the initial stages of the event, which caused the delay in initiating the TLR process. 3. TLR Levels, timing (CST) and relief amounts TLR LEVEL

Effective TIME (CST)

Flowgate Relief Entered into IDC (MW)

Number of transactions curtailed, priority, and magnitude of transactions

4 0754 0 ATCo Redispatching. 4 0848 0 ATCo Redispatching. 4 0931 0 ATCo Redispatching. 4 1030 0 ATCo Redispatching. 4 1139 0 ATCo Redispatching. 4 1231 0 ATCo Redispatching. 4 1329 0 ATCo Redispatching. 4 1426 0 ATCo Redispatching. 5a 1600 23 No Transactions Curtailed-ATCo

Redispatching for both 7-F and NNL responsibilities.

5a 1700 40 No Transactions Curtailed-ATCo Redispatching for both 7-F and NNL responsibilities.

5a 1800 29 No Transactions Curtailed-ATCo Redispatching for both 7-F and NNL responsibilities.

5a 1900 18 No Transactions Curtailed-ATCo Redispatching for both 7-F and NNL responsibilities.

4 1928 0 ATCo Redispatching. 3a 2100 0 No Non-Firm transactions available. 3a 2200 0 No Non-Firm transactions available. 0 2320 End Event No Non-Firm transactions available. 4. Transmission and generation outage or changes from prediction that may have

contributed No significant forced transmission or generation outages contributed to this loading problem.

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5. Procedures implemented prior to hold/curtailment ATCo voluntarily re-dispatched generation in the area in order to mitigate the loading on Flowgate 3014 prior to the issuance of TLR 5. 6. Compare Complete Transaction Curtailme nt List with the Whole Transaction List as

generated by the IDC, before and after curtailments There were no non-firm transactions that impacted Flowgate 3014 by 5% or greater during this event, therefore none were curtailed and reloaded as required by NERC policy. Firm transactions impacting flowgate 3014 by 5% or greater were allowed to continue flowing, as ATCo elected to redispatch generation resources in order to compensate for the impact of these transactions in lieu of curtailing them. As a result, the impact of these transactions on the constrained flowgate was negated as required by NERC policy. 7. Known Transactions not in the IDC and actions taken There were no known transactions not in the IDC at the time this TLR was in effect. 8. SCIS or other system messages Information was provided to NERC Security Coordinators via the NERC IDC. The IDC automatically sent TLR Level information via the SCIS. Curtailment information was sent out via the MISO Messaging System to the MISO Control Areas. At 09:00 CST Time Error Correction “S” began. At 18:00 CST Time Error Correction “S” ended. 9. State estimator snapshots and security analysis including contingency analysis or

stability analysis along with any other recorded data indicating the need for TLR Relief requirements were calculated by using real-time loadings on monitored and contingent elements. Post-contingency flow was calculated using the LODF (Line Outage Distribution Factor). Security analysis results were compared and confirmed with ATCo Operators. The ATCo Operating Guide for the loss of Paddock 345/138 T21 Xfmr significantly increases the operating limit for the Flowgate. The Operating Guide consists of 3 basic steps.

a. Open 646-S at Rockdale (Jefferson 138 KV line) LODF is 19.8%

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b. Open 242-S at Academy (Box Elder-Rockdale 138 KV line) LODF is 20%

c. Call Commonwealth-Edison via hotline and request open on 15503 at Nelson

(Cordova 345 line) Expected relief per CE studies is 10MVA. According to Midwest ISO studies, this Operating Guide would cause no immediate base-case overloads. Following the loss of Paddock 345/138 T21, the reconfiguration of the transmission system in steps a-c would reduce overloading on the Rockdale 345/138 Xfmr from approximately 117% to approximately 101%. 10. ATC Limitations before, during, and after the event

On Tuesday February 19, 2002, AFC calculation results showed firm available capability for Flowgate 3014 for the next day due to modeling issues created in part from inaccurate generation dispatch merit order data being submitted to MISO. The Christiana units, which impact flows on Flowgate 3014 significantly, are combustion turbine peaking units and were incorrectly modeled as on- line and generating in the AFC calculations. This resulted in less estimated flow on Flowgate 3014 and more AFC than should have been available. The Christiana units were ultimately brought on-line during the event as redispatch generators to mitigate flow on Flowgate 3014. The indicated positive AFC resulted in a 150 MW daily firm reservation from CE to ALTE being approved 2/19/02 for 2/20/02. Three 50 MW transactions were scheduled utilizing the 150 MW reservation and subsequently resulted in 22 additional MWs impacting Flowgate 3014. 11. Description of actions taken to avoid future hold/curtailments ATCo is in the process of adding a third Rockdale 345/138kV Transformer that is now scheduled to be in service July, 2002 that should eliminate the need for TLR on Flowgate 3014. MISO has corrected the problem of inaccurate merit order dispatch data being introduced into the AFC process and is improving AFC calculation results.

Available Flowgate Capability (AFC) on Flowgate 3014 Rockdale 345/138kV Transformer #2 for the outage of Paddock 345/138kV

Transformer1 Date Hours (EST) Firm (MW) 2 Non-Firm (MW)

2/19/02 0000 – 2400 35 Ranged from 74 to 198 2/20/02 0700 – 0800 Not Available3 Ranged from 81 to 2044

1: MISO calculates AFC rather than Available Transmission Capability (ATC) and offers transmission service via OASIS on the basis of AFC. 2: Last AFC value remaining on 2/19/02 for firm service on 2/20/02. 3: Firm service is not available for same day service. Therefore, firm service was not available for 2/20/02 on 2/20/02. Non-firm AFC was zero during the event. 4: No firm or non-firm service impacting flowgate equal to or greater than 5% was granted when the event during the event when TLR levels were 3 or higher.

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12. Re-dispatch actions taken Prior to the issue of TLR level 5A, ATCo performed voluntary re-dispatch in order to mitigate the loading on Flowgate 3014. Once the TLR 5A was issued, both ComEd and ATCo performed re-dispatch in order to cover their NNL responsibilities, in addition, ATCo performed re-dispatch in order to protect all priority 7-F transactions sinking in ATCo.

ATCo implemented redispatch for ALTE NNL, MGE NNL, and all Priority 7 Firm Transactions

Hour Ending (CST)

ATCo Total

Required Redispatch

(MW)

Units Redisptched Redispatch (MW)

GSF Relief Provided

(MW)

1700 13.3 MGE(BLT) to ALTW Sheepskin to ALTW Total

50 36

0.170 0.167

8.500 6.012 14.512

1800 23.9 Christiana to ALTW Sheepskin to ALTW MGE (FCH BLT) to ALTW Total

25 36 50

0.250 0.167 0.170

6.250 6.012 8.500 20.72

1900 17.9 Christiana to ALTW 100 0.25 25 2000 11.2 Christiana to ALTW 100 0.25 25 2100 0 Christiana to ALTW 100 0.25 25

ComEd implemented redispatch for ComEd NNL

Hour Ending (CST)

ComEd Total

Required Redispatch

(MW)

Units Redisptched Redispatch (MW)

GSF Relief Provided5

(MW)

1700 9.6 See Table

Below6 1800 16.1 Christiana to CE See

Table Below7

1900 11.1 Christiana to CE 50 0.28 148 2000 6.8 Christiana to CE 150 0.28 429

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Hour Ending (CST)

5: ComEd actions during 02/20/02 NERC TLR level 5 Event

General comment: After being informed of the initial NNL obligation at approximately 15:35 effective at 16:00, ComEd attempted to access the NERC GSF viewer, only to find out that it was inoperable. ComEd waited approximately 30 minutes before receiving a faxed document containing shift factors from their Reliability Authority. Evaluation of possible generation redispatch options could not be performed until this information was available.

1700 6: ComEd’s NNL relief obligation was calculated to be 9.6 MW. With no viable internal redispatch options and limited time to investigate external sources for redispatch, ComEd offered a post-contingency transmission reconfiguration that would relieve 10 MW from flowgate #3014. This reconfiguration option was communicated to the American Transmission Company and was available, if needed, throughout the event.

1800 7: ComEd’s NNL relief obligation was calculated to be 16.1 MW. Prior to the hour, after further discussions with the American Transmission Company, ComEd requested Exelon Powerteam to buy at least 70 MW from Duke Energy to be sourced off of the Christiana plant within the ALTE control area. A Christiana to ComEd transaction had a calculated 28% distribution factor on flowgate #3014. Due to unit starting issues, and tagging problems, schedules did not begin flowing until 18:30.

1900 8: ComEd’s NNL relief obligation was calculated to be 11.1 MW. Due to unit starting issues, and tagging problems, schedules did not begin flowing until 18:30. At that time there was a 50 MW schedule from ALTE (sourced off of the Christiana plant) to ComEd.

2000 9: ComEd’s NNL relief obligation was calculated to be 6.8 MW. For this hour there was a 150 MW schedule from ALTE (sourced off of the Christiana plant) to ComEd. This schedule also ran at this level for the following 3 hours due to ‘minimum take’ requirements.

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13. If Firm transaction curtailments took place, description of Transactional Contribution Factor calculation and results as well as how necessary relief was obtained through network service and native load contributions.

According to the IDC the there were small generation to load distribution factors (GLDF) that were attributed to ALTE and MGE, as well as a larger GLDF attributed to ComEd. The Network and Native Load (NNL) responsibilities ranged from 6.8 MW to 16.1 MW for ComEd during the TLR 5a event. The ALTE NNL requirement ranged from 0.7 MW to 1.6 MW and the MGE NNL requirement ranged from 0.9 MW to 2.0 MW. In addition, the priority 7-F transaction curtailments ranged from 9.6 MW of relief to 20.3 MW of relief. The relief associated with these responsibilities was obtained exclusively through the re-dispatch of generation. The amounts of relief that were achieved on the Flowgate due to the re-dispatch performed are shown in ITEM 12 above. Time Hour

Ending (CST)

ComEd NNL (MW)

ATCo (ALTE)

NNL (MW)

ATCo (MGE) NNL (MW)

ATCo Priority 7

Firm Transactions

(MW)

Total Redispatch

(MW)

1700 9.6 0.9 1.2 11.2 23 1800 16.1 1.6 2.0 20.3 40 1900 11.1 1.1 1.4 15.4 29 2000 6.8 0.7 0.9 9.6 18

14. Other options considered before/during to avoid hold/curtailment. Before the curtailment, ATCo provided voluntary re-dispatch. ATCo was not obligated to provide further re-dispatch, and as a significant portion of flows on the element were due to Commonwealth Edison Network and Native Load service, a TLR 5 was issued.

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Appendix A: NERC TLR Log for Flowgate 3014

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Appendix B – Weather temperatures during event.