Palo Verde to Westwing Double Line Outage Probability Analysis SRP
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Palo Verde to Westwing Double Line Outage Probability Analysis SRP Tatyana Len Dhaliwal [email protected] <mailto:[email protected]> Executive Summary This report details the mitigating factors and a double contingency outage analysis of the Palo Verde to Westwing lines 1 and 2. This outage is considered of such low probability of occurrence and recurrence, that it warrants submittal to the WECC Phase I Probabilistic Based Reliability Criteria (PBRC) Performance Category Evaluation (PCE) Process. Under this process, a project with an accepted Mean Time Between Failure (MTBF) in the range of 30 to 300 years may be adjusted to Category D, but with the added condition of “no cascading” allowed. A project with a MTBF in excess of 300 years is considered an “Extreme Event” in the same sense as all other events in the NERC Category D. This report follows the Probability Reliability Evaluation Work Group (RPEWG) recommended steps provided in Appendix I, Figure 10 RPEWG Recommended Analysis Steps. Analysis of the Palo Verde to Westwing Lines 1 and 2 double contingency (N-2) qualifies to be moved to Category D based on the following statistical analysis and mitigating factors: 1) An MTBF estimated by a traditional statistical reliability analysis method is on average once in 2824 years. 2) In the 11 years of accurately recorded outage history in electronic format, there has never been a double contingency outage of the Palo Verde to Westwing lines. Evidence suggests that since both lines were in service, this outage has not ever occurred. 3) Both Westwing and Palo Verde switchyard use breaker and a half arrangement. 4) As a result of the Rudd line installation, the Palo Verde to Westwing lines 1 and 2 outage is no longer the most critical outage. 5) According to UFSAR, the failure of this line at the crossing over the PV-WW 1 and 2 is no longer postulated under the revised 10CFR50.59 rules. Therefore grid studies need not address this scenario. 6) The Robust design features are overhead ground wires, lines are built 130 feet apart (centerline to centerline) with towers designed to fail in the middle. The failure and fall of one tower does not jeopardize the continued safe operation of the other tower. 7) Palo Verde to Westwing 500kV lines are located outside the areas of consideration for air traffic. The elevation of the lines in beyond and beneath the criteria FAA defines for consideration as an obstacle or hazard. 8) The isokeraunic level near Palo Verde and Westwing is one of the lowest in the Western US, ranging from 1.0 strikes per square mile per year near Palo Verde to 2.5 strikes per square mile per year near Westwing switchyard. 9) The risk of earthquakes in Maricopa County is the lowest in the Western US. 10) The risks of flood, snow, and fire are negligible. 11) The PV-WW foundations are over designed in the range of 137 to 199%. 12) The lattice tower design is conservative for weather related loads. 13) Lines are designed with state of the art spacer dampers to control conductor motion. 14) The insulation level exceeds EPRI’s guidelines. 15) Electronic protection is provided by redundant microprocessor based technology with communication via fiber optics and digital microwave systems on independent paths. A third microprocessor based relay system operating in current differential scheme is provided for backup protection. 16) SRP aggressively maintains the lines with twice yearly patrols, bird guard systems in place, an insulator-washing program, and a spacer damper replacement program. In summary, based on an MTBF estimated by traditional statistical reliability analysis of 2824 years and excellent design and maintenance practices, it is recommended that this N-2 outage be moved to Category D (Extreme Events) with no other conditions or requirements. Description of the Palo Verde to Westwing Lines 1 and 2 Path. SRP (Salt River Project) is a major multipurpose reclamation project comprising two principal operating groups: the Salt River Project Agricultural improvement and Power district, a political subdivision of the state of Arizona; and the Salt River Valley Water Users’ Association, a private corporation. The district provides electricity to more than 625,000 customers in the Phoenix area. It operates or participates in seven major power plants and numerous other generating stations, including thermal, nuclear, and hydroelectric sources. The District serves a 2,900-square-mile area spanning portions of Maricopa County (the metropolitan Phoenix Area), Gila, and Pinal counties in central Arizona. The two 500kV transmission lines discussed in this report connect the Palo Verde Nuclear Generating Station near Wintersburg to the Westwing Receiving station, north- northeast of Sun City West. The line length is 45.1 miles. The lines are located to the west of the Phoenix metropolitan area. Below is the photograph of the Westwing yard looking south; the Palo Verde to Westwing lines are to the right. Below, are two photographs of the Palo Verde to Westwing lines towers. The photo below depicts a tower on Palo Verde to Westwing Line 1 near the Westwing substation. The photo above depicts a tower on Palo Verde to Westwing Line 2 near the Westwing substation. From the Westwing substation the lines proceed west for 19 miles, then south west for 3.1 miles, then 9.5 miles in the south direction, then 8 miles in the south west direction, 4 miles west- south west, and finally west for the last 1.5 miles to Palo Verde yard, as shown in the diagram below: Two to three miles outside of the Westwing substation, the Mead to Phoenix 500kV line crosses over the two Palo Verde to Westwing lines. Here are some photographs of the crossing: 27.6 miles from Westwing, the two Palo Verde to Westwing lines cross over the Liberty to Mead 345kV line, as shown below: 29.6 miles from Westwing, the two Palo Verde to Westwing 500kV lines cross over the Harcuvar to Buckeye 230kV line and the Parker to Liberty 230kV line, as shown below: The new Palo Verde to Rudd line is in the same corridor with the two Palo Verde to Westwing lines for several miles outside of Palo Verde switchyard. The Rudd 500kV is the rightmost line. Here is the photo of the Palo Verde to Westwing lines (the two rightmost lines) emanating from the Palo Verde switchyard. System Configuration and Fault Analysis Palo Verde – Westwing Double Line Outage Reclassification The Palo Verde – Hassayampa Hub area is a major electrical energy trading hub in the United States. There are currently Independent Power Producer generators at the Palo Verde hub in addition to the existing Palo Verde Nuclear Generating Station. This year there are 230kV & 500kV transmission system enhancements and new generator interconnectors synchronizing to the transmission system. Current Current Jun/2003 Generators Total Equivalized Equivalized Palo Verde Nuclear(existing) 3861MW 3861MW 3861MW Duke Arlington Valley(existing) 600MW 600MW 600MW Pinnacle West Red Hawk(existing) 1000MW 1000MW 1000MW Sempra Mesquite(2003) 525MW 525MW 1050MW PGE National Harquahala(2003) 1148MW 1148MW 1148MW TECO Panda Gila River(2003)(network) 1560MW 780MW* 1040MW* Total Generation Value 8694MW 7914MW 8699MW *The TECO Panda Gila River interconnection is not a radial connection to the Palo Verde – Hassayampa hub. This interconnection has a 230kV tie into the Gila Bend – Liberty circuit. This generation interconnection has a reduced interaction, 0.5 to 1 as compared to the direct interconnectors, at the Palo Verde – Hassayampa hub, as measured in enhancing generating capability and requirement of curtailment. As evidenced by the above list, there is much existing and new interconnecting generation at the Palo Verde – Hassayampa hub. There are currently 6 - 500kV circuits emanating out of the Palo Verde – Hassayampa hub; Palo Verde – Westwing #1 & #2, Hassayampa – Jojoba – Kyrene(Palo Verde East) & Palo Verde – Devers, Hassayampa – North Gila(Palo Verde West) and Palo Verde to Rudd lines. Operating studies were performed in 2002 to determine the amount of generation that could be safely interconnected to the Palo Verde – Hassayampa hub without Remedial Action Scheme (RAS) and with RAS. Spring 2003 studies were performed with the same methodology, to determine the amount of generation that could be in service with and without RAS. The conclusions of this Spring 2003 study is a little different in that there is a thermal limit that is the upper bound of allowable safe generation. This limit is a simultaneous loading of the 500kV lines to the east and to the west of the Palo Verde – Hassayampa hub. Only 7,301MW of equivalized generation may operate at one time, this is the thermal limit. The thermal limit is an n-0 limit. The interconnection of a 500kV circuit from Palo Verde to Rudd, a local load serving circuit to serve SRP and APS load was energized in June of 2003 and has increased the thermal capacity of the 500kV circuits emanating from the Palo Verde – Hassayampa hub. The amount of MVARs that are produced or absorbed by the Palo Verde nuclear units determines the amount of generation that has to be used in the RAS for safe operation. As the amount of MVARs absorbed by Palo Verde increases, the amount of interconnector generation that has to be used in the RAS increases. The most limiting condition studied was with the Palo Verde 500kV bus at 525kV and the Palo Verde units absorbing 800MVARs. These constraints come from the operators of the Palo Verde Nuclear Generating Station. New interconnector generation, a 4th Panda Gila River unit and the 2nd Mesquite unit are synchronizing after the Rudd line in-service date. Therefore, the rightmost column in the above table will also have the new 500kV circuit in service.