WALC Operations Study Report

2008-2009 Winter

OPERATING

STUDIES

REPORT

WESTERNDESERT SOUTHWEST REGION

August 21,2008

Prepared by

Nick Saber

WALC BA OPERATING COMPREHENSIVE STUDY REPORT

2008-2009

Table of Contents

PAGE

  1. Executive Summary 1
  1. Purpose2
  1. Background 3
  2. Conclusions 7
  1. Findings 8
  2. Power Flow Analysis
  3. Short Circuit Studies
  4. Stability Analysis
  1. Study Assumptions 12
  1. Methodology 13
  1. Base Case Development 14
  1. Operating Nomograms 15
  1. Blythe Matrix 36

REFERENCES

  1. Power System’s Dispatcher SOP 510
  1. Facility Ratings Methodology, May 2007
  1. SYSTEM OPERATING LIMITS (SOL) METHODOLOGY

FOR SYSTEM PLANNING May, 2007

4. DSW Voltage Stability Assessment

August 31, 2007 - Appendix D - Detail Listing of System Voltage Performance Violations

APPENDICIES

Appendix AStudy Plan Page 37

Appendix BWALC Study Criteria

Appendix C Reserved

Appendix DStability Plots (PDF)(available upon request)

Appendix E Blythe Matrix (.xls)

Appendix F Distribution Factors (.xls) )(available upon request)

ATTACHMENTS

(available upon request)

Attachment A WECC approved cases and associated dynamic files

Attachment B.1 study results for N-0

Attachment B.2 study results for N-2

Attachment B.3 category C cases and dynamics

Attachment C planning methodology and procedures

Attachment D Arizona Security Manual -year 08

Attachment E past season/years studies

Attachment F Extended List of DSW N-1 Outages

Attachment G Extended List of WALC N-2 Outages

Attachment H DSW Grounding Requirements

WALC Operations Study Report

1.0EXECUTIVE SUMMARY

The findings from this transmission system assessment support that the Western DSW Transmission System can performreliably and as required in the NERC/WECC applicable standards shown below.

This comprehensive system operating study is performed to confirm the system operating limits SOL for the 08-09 Winter operating season. Since the results of the study do not show any WALC system violations no revisions or updates to present Standard Operating Procedures are planned at this time.

The findings of these studies are documented in this Report which will be posted on Western’s OASIS Web site and issued to each adjacent Balancing Authority and made available to others upon request.

2.0PURPOSE

The purpose of this study is to examine WAPA Lower Colorado Balancing Authority (WALC) and Western’s Desert Southwest Region (DSW) transmission system performance in the 2008 -2009 winter seasonand to confirm the SOL for the 08-09 operating seasons.

The report examines potential facility overloads as a result of N-1 and N-2 category outages. If results of studies demonstrate the need foroperating procedures to be reviewed and/or developed to address Operator actions to be made to the DSW System in accordance with the applicable NERC/WECC Reliability Standards. These adjustments may include implementing a remedial action scheme (RAS) or possible generation re-dispatch within the DSW Balancing Authority.

The following NERC Reliability Standards are applicable to this study:

Standard / Req. / Title
FAC-011 / R2.2, R2.3, R5, and E1 / System Operating Limits Methodology for the Operations Horizon
TOP-002-2 / R2,R3,R4,R10,R11 / Normal Operations Planning
TOP-004-1 / R1,R2,R6 / Transmission Operations
TPL-001-0 / R1.1,R1.3.2,R1.3.5-R1.3.9,R3 / System Performance Under Normal Conditions
TPL-002-0 / R1.1,R1.3.1,R1.3.5-R1.3.12,R3 / System Performance Following Loss of a Single BES Element
TPL-003-0 / R1.1,R1.3.1,R1.3.3,R1.3.5-R1.3.12,R3 / System Performance Following Loss of Two or More BES Elements

3.0BACKGROUND

Western’s DSW transmission system is sensitive to the operations of the surrounding EHV transmission system and loadings of the Arizona – California tie lines including East-of-the-River (EOR) and West -of -the River transmission path. Western DSW participates, reviews and comments on regional studies that may impact its transmission system. Western DSW participates with the California Operating Studies Subcommittee (OSS). The OSS members include the Los Angeles Department of Water and Power, Nevada Power Company, San Diego Gas and Electric, Southern California Edison, PG&E, CAISO, Western DSW. The OSS is primarily concerned with the 500-kV transmission lines and the Pacific DC intertie limitations. Also, Western DSW is a member of the Arizona Coordinated Transmission Study Group (WATS), this group is made up of entities within the ArizonaValley and USBR, its focus is on system changes affecting transmission system performance in Arizona.

DSW Real-Time Operating Engineer conducts outage studies using base cases developed from WECC OTC studies and modified for the season and near term operating conditions. Scheduled outages and or operating problems are identified in this process and lower OTC limits are communicated to the Operators to protect the system. Also, RDRC day-ahead study results are reviewed daily and RDRC directives implemented when needed.

The DSW Real-Time Operations Engineer participates in weakly and or daily conference calls with other Operations staff from neighboring utilities during summer peak and abnormal events. Additionally, Western DSW participates in the seasonal outage coordination meetings conducted by RDRC.

Dispatcher has 30 minutes to bring a transmission element that is in an overload back to operate within NERC/WECC operating criteria.

Dispatcher has authority to shed load or open an overloaded circuit. When an overload is detected that may be a result of n-1 system condition or over scheduling of a path, the EMS SCADA system first alarms and gives annunciation that a lower set point 90-95% of SOL is reached if curtailments are not reached SCDA EMS follows with an alarm at 110% SOL this requires immediate dispatch corrective action.

Dispatcher communicates with scheduling entity making requests for curtailment. Dispatcher has the authority to shed load. For the case of the Blythe area transmission system WALC has implemented a RAS scheme to automatically curtail generation of the Blythe generating plant for an overload condition on any of the transmission lines interconnected to the Blythe 161-kV bus

Western DSW participates in RMR studies and operates its system in a manner that does not require load shedding for single contingency conditions.

4.0CONCLUSION

  1. Because there has been no topology change to the DSW transmission system from the 07-08 summer season comprehensive study, the operating studies for the 08-09 Heavy Winter operating season are performed as case checks using the WECC operating season base case. The study performed case checks and n-1, n-2 power flow runs to ensure that safe and reliable operation of the DSW system in accordance with present operating procedures and that the nomograms are valid for the current operating season.
  2. For TPL-002 category B compliance N-1, steady state N-1 power flow cases were ran. The power flow case review and assessment indicate no WALC system violations. The results of the three phase to ground fault with normal clearing runs using WECC System Performance Criteria for category B analysis also show no WALC system violations.
  3. For TPL-002 category B compliance N-1, 199 steady state N-1 power flow cases were ran (comprising all of WALC”s BES lines and joint tie lines). The power flow case review and assessment indicate no WALC system violations. The results of 86 three phase to ground fault with normal clearing runs using WECC System Performance Criteria for category B analysis also show no WALC system violations. For the outage list and results
  4. For TPL-003 category C compliance nine credible (same tower, common right-of-way, etc) N-2 steady state power flows and thirty N_2 with delayed clearing stability runs were made.The power flow case review and assessment as well as the stability runs indicate no WALC system violations.
  5. Under system normal conditions for high or moderate power flows on the DSW transmission system, there are no violations of NERC/WEECC Standards and Criteria. There are no overloads on the DSW lines following an N-1 outages. WALC has Special Operating Procedures to mitigate overloads in the Blythe area associated with the operation of the Blythe Energy generation. Also there is the GlenCanyon unit drop procedures for use in the case of loss of a transmission element on the Glen Canyon Pinnacle Peak Transmission system.
  6. The DSW annual Fault Duty analysis shows that fault duty continues to be below equipment ratings at all DSW as well as any of the surrounding substations, one bus away. There is no issue of encroachment of fault currents on the existing breaker ratings at all DSW Substations.. Recommendations have been given to Maintenance to plan for replacement of certain breakers at PinnaclePeak and GlenCanyon because these breakers were getting close to the 95% fault current encroachment margin.
  7. Results of studies investigating worst-case N-1 outagesindicate that there is no stability problems at any IPP generating station, or at any of the federal hydro plantsintegrated within the WALC balancing authority. Stability was maintained for all faults studied without generator dropping or other remedial action schemes. Only in the case of a close in 3 phase fault on the Julian Hinds – BuckBlvd 230-kV line and for highly stressed EOR case unless the Blythe Energy generator reactive output is high we may observe a violation of the WECC voltage dip and dip duration criteria. In all stability runs we have observed positive rotor damping. Operating studies completed by Western validate the need for Blythe generator curtailment as shown on the Blythe Matrix.
  8. Results of stability studies showed no system performance violations occurred for NERCCategoryB (single contingency) conditions, for three phase faults with normal (5 cycle) fault clearing time.
  9. Stability Studies for NERCC stability contingencies, generator stability for several generators within the WALC foot print can be a problem. The critical NERCC stability contingencies conducted for the GlenCanyon and Griffith plants show that 1) GlenCanyongenerators can become unstable for stuck breaker condition It was found that the minimum fault clearing time at GlenCanyon can be as short as 6 cycles. Also,at Griffith the minimum fault clearing time is 9 cycles.
  10. Further stability studies are needed to ensure adequacy of generator protection schemes at Federal Hydro plants specifically the GlenCanyon, Hoover, Davis and Parker plants. The studies will be conducted jointly with Reclamation.
  11. Under voltage conditions are observed especially with IPP generators off. Further voltage studies will be conducted to examine the need for distributed shunt capacitors and or under voltage automatic load shedding.

5.0FINDINGS

5.1Findings – Power Flow Analysis

5.1.1The power flow studies conducted examined the operating performance for heavy summer and winter cases during normal and contingency conditions based on line flows and voltage profile for various operating conditions. All single and credible multiple DSW contingencies and critical contingencies for EHV tie lines in Arizona were run to determine any line overload or voltage problems. No system performance violations occurred for NERCCategoryB (single contingency) conditions.

Reference is made to SOP 510 which lists continuous and emergency ratings for all DSW transmission lines and transformers.

5.1.2With Griffith Generation off, with Davis McConnico and Griffith – Peacock in an n-2 condition will cause a voltage collapse at the Peacock 230-kV bus, Hill Top 230-kV bus 0.765 pu and RoundValley. Also, an overload on Prescott Wilowlk 123%., as shown on power flow plots . Recommended Operator action includes possible load shed: 40 mw UES load tripped at Griffith 69-kV, 33 MW UES load is tripped at Hilltop 69-kV and APS load at Hilltop.

5.1.3Results show that the Liberty-Peacock line does not need to be derated when both its series caps are bypassed accordingly APS was requested to make a change to this effect in the "Arizona Security Manual" so that the Manual:

1. Do not derate the Liberty-Peacock 345 kV line if only the Mead 345 kV series caps are bypassed; but the Liberty 345 kV series caps are switched-in and the Liberty 230 kV PST is available.

2. Do derate the Liberty-Peacock 345 kV line if either the Liberty 345 kV series caps are bypassed and/or the Liberty 230 kV PST is unavailable.

5.1.4With high flows south on the GlenCanyon-PinnaclePeak lines the loss of either one of the two 345/230-kV transformers causes and overload on the remaining transformer. The Operator will alleviate the overload using the Glen - Shiprock phase shifting transformer. A recommendation is made for long term solution to add a third 345/230 transformer.

5.1.5For the following N-2 conditions reduce BEP from 520 MW to a generation level that can be sustained without going over the emergency limit of any of the lines out of Blythe.

  1. For the IOS outage of Blythe – Niland 161 kV transmission line condition and a forced outage of the Blythe – Blythe SCE 161 kV line, to reduce the overload on the Blythe – Knob 161 kV transmission line reduce the BEP to a maximum of 320 MW.
  2. For the IOS outage of Blythe – Blythe SCE 161 kV transmission line condition and a forced outage of the Blythe – Knob 161 kV line, to reduce the overload on the Blythe – Niland161 kV transmission line reduce the BEP to a maximum of 340 MW.
  3. For the IOS outage of Blythe – Knob 161 kV transmission line condition and a forced outage of the Blythe – Blythe SCE 161 kV line, to reduce the overload on the Blythe – Niland 161 kV transmission line reduce the BEP to a maximum of 340 MW
  4. For the IOS outage of Blythe – Headgate 161 kV transmission line condition and a forced outage of the Blythe – Blythe SCE 161 kV line, to reduce the overload on the Blythe – Niland 161 kV transmission line reduce the BEP to a maximum of 430 MW.
  5. For the IOS outage of Blythe – Parker 161 kV transmission line condition and a forced outage of the Blythe – Blythe SCE 161 kV line, to reduce the overload on the Blythe – Niland 161 kV transmission line reduce the BEP to a maximum of 430 MW.
  6. For the IOS outage of PaloVerde – N. Gila 500 kV transmission line condition and a forced outage of the Blythe – Knob 161 kV line, to protect and reduce the overload on the Blythe – Niland 161 kV transmission line below emergency reduce the BEP to a maximum of 380 MW.

5.2Findings - Short-Circuit Studies

The Study compared the total bus fault current at the faulted station against the station’s lowest rated breaker (in terms of its symmetrical interrupt rating). When the total bus fault current encroached on or exceeded 95% of a breaker interrupt rating, the Study judged the breaker to be inadequately sized and a candidate for replacement by the Project. Conversely, when the total bus fault current did not exceed a breaker interrupt rating, the Study judged the breaker is not a candidate for replacement.

Short-circuit studies showed the need for certain breaker replacement. Short-circuit study results are available upon request.

The DSW implements a program for breaker replacements if the breaker approaches or is over the 95% margin. Fault Studies identified the following:

  1. 8 circuit breakers that are underrated at PinnaclePeak substation. The DSW Maintenance Department is proceeding with plans for replacement. G5200 will purchase two new breakers in fiscal year 2008 (3282 and 2282) and installed in the fall of fiscal year 2009. Breakers 3482 and 3682 will be purchased at the beginning of fiscal year 2009 (October 2008) to be installed in the spring (March-April 2009) of that fiscal year.

* FY2008: 3 breakers (Fall – 1. Spring = 2).

* FY2009: 2 breakers (Fall - 1. Spring = 1).

* FY2010: 3 breakers (Fall - 2. Spring = 1).

PPK breakers 230-kV breakers are 50-kA plan to replace margin is 47.5 kA:

Breaker 182 maximum fault current is 47.9 kA which is over the 95% margin and should be replaced. This is the breaker for transformer KU1A.

Breaker 2682 maximum fault current is 48.361 kA which is over the 95% margin and should be replaced. This is a tie breaker for the North main and transfer buses.

Breaker 3082 maximum fault current is 48.327 kA which is over the 95% margin and should be replaced. This is the breaker for the SRP West bus connection.

Breaker 3282 maximum fault current is 48.361 kA when switch 3185 is closed. If switch 3185 is open, the maximum fault current is 48.325 kA. In either case, this breaker is over the 95% margin and should be replaced. This is the tie breaker between the South and North main buses.

Breaker 2282 maximum fault current is 47.9 kA which is over the 95% margin and should be replaced. This the breaker for transformer KU3A.

Breaker 3482 maximum fault current is 48.361 kA which is over the 95% margin and should be replaced. This is the tie breaker for the South main and transfer buses.

Breaker 3682 maximum fault current is 48.348 kA which is over the 95% margin and should be replaced. This is the breaker for the SRP East bus connection.

2.Replace the 25kV circuit breaker 4032at GlenCanyon substation. The circuit breaker is under rated. The circuit breaker was manufactured in 1986.

5.3Findings -Transient Stability Studies

The transient stability studies focused exclusively on 3-phase bus faults on the WALC transmission system. The Study examined a bus fault on each of the substations within WALC BA. The transient stability studies simulated both normal fault clearing under NERCCategoryB as well as normal and delayed fault clearing under NERCCategoryC.

All contingencies showed damped oscillations and do not result in large changes to the voltage stability characteristics of DSW system. All single contingencies were within the 7% post-transient limit for percent voltage change. All double contingencies were well within the 10% post-transient limit for percent voltage change.

A 3-phase fault was simulated near each bus marked with an asterisk.

All studies were run with PSS on -unless otherwise noted.

Appendix?? includes transient stability plots for simulations run.. Reference is made to Voltage Stability Study Report dated ??.

The Study found that a stuck breaker condition at GlenCanyon lines simulated with delayed (15 cycle) fault clearing causes the Glen units to go out of step. Maximum clearing time was found to be 6 cycles. DSW and Reclamation are discussing accuracy of model.

The Study used a modified version of the WECC-distributed alldyns.p EPCL program to batchrun the transient stability simulations in version 16 of the GE PSLF/PSDS software.

The Study evaluated generator stability by visually examining the plots of relative rotor angles (in degrees), terminal voltages (in per unit), generator electrical active power (in MW), generator shaft speed (in per unit), and bus frequency (in Hz). The Study evaluated transient dip and dip duration criteria by using the Worst Condition Analysis (WCA) command in the General Electric PSDS software in a batch-run program. WCA began two cycles after fault clearing.