3 IntroductionThe I-5 Corridor extends through BPA’s system from Canada to the border of California and Oregon and is a major north to south transmission path through BPA’s system.The Tacoma, Southwest Washington, and Northwest Oregon load areas are served by the I-5 Corridor main grid transmission system.Currently the I-5 Corridor is one of BPA’s most congested paths with the highest loading during peak summer load conditions combined with high north to south transfers through the northwest from Canada to California.
4 Problem DescriptionUnder high north to south flow conditions critical 500kV line outages can cause voltage instability and overloads on the underlying 230 and 115 kV systems.The current practice to mitigate these problems is to use a remedial action scheme (RAS) to trip key generation in the Northwest and Canada to reduce flows through the I-5 corridor.In the event of any of these outages as much as 2700MW of generation can be dropped.
5 Project PurposeThe purpose of the proposed plan of service is to address the following:Transmission service requests (Long-term)There are numerous requests in the queue which affect the I-5 CorridorGeneration interconnection requestsCurrently there are several proposed new generating projects that have an impact on the I-5 corridor transmission system. These projects are located between Satsop and Longview and have a combined capacity of 1476MW.Increasing summer peak loads and the existing contractual obligations to serve themReduce dependence on existing RAS while maintaining transmission system reliability
6 Generation levels (maximum output used in studies) Study AssumptionsBase cases to be usedBPA’s peak summer load budget base casesThe years 2008 (near term) and 2012 (long term) were studiedGeneration levels (maximum output used in studies)Chehalis Power Project MW(PGE) Beaver MW(Clark) River Road MW(PACW) Swift MW(PACW) Yale and Merwin MW(PGE) Port Westward MWMint Farm MW(Grays Harbor) Satsop MW(Pacific Mountain Energy Center) Kalama 600MWLevels studied for critical cut planes/interties affecting the area:Canada-Northwest 2000 to 2850 MWCalifornia-Oregon Intertie 3300 to 4800 MWNorth of John Day 7000 to 8400 MW
7 Area loads forecasted for summer 2008 Study AssumptionsArea loads forecasted for summer 2008PGEWest Metro = 1980MWEast Metro = 1317MWPAC Portland area = 465MWClark County = 659MWThermal limits of critical equipment (summer ratings at 30° C ambient temp)Chehalis-Longview #1 and #3 230kV lines, 1840Amps to tap; 1070Amps individuallyHolcomb-Naselle 115kV line, 430AmpsRoss-Woodland 230kV line, 1070AmpsLongview-Lexington 230kV line, 1070AmpsTrojan-St. Mary’s 230kV line, 1315AmpsMerwin-St. John’s 115kV line, 673AmpsKeeler-St. Mary’s 230kV line, 1757Amps
8 Remedial Action Scheme (RAS) Study AssumptionsRemedial Action Scheme (RAS)The maximum allowable generation dropping for RAS was limited to 2700MW for these studiesRAS generation dropping priority was based on effectiveness as follows:Available I-5 Corridor generation: Chehalis, Big Hanaford, Fredrickson, and new generation as applicableBC Hydro: Revelstoke and MCAUpper Columbia: Grand Coulee and Chief JosephBC Hydro generation armingDefined by the equation 1.5*(IC-800), IC = the Ingledow-Custer flowGeneration dropping at BC Hydro was limited to a maximum of 1850MW.Dropping the generation is an “all or nothing” scheme.In this study it was assumed that if the sum of the I-5 and BC Hydro generation armed exceeded the maximum RAS limit of 2700MW, then generation at BC Hydro would not be dropped. Generating units at Upper Columbia would be dropped instead.South of Chehalis Sectionalizing Scheme (SOCSS)Opens the Chehalis-Longview 230kV and Holcomb-Naselle 115kV lines in the event of an overload following a Paul corridor 500kV double line loss. This scheme is armed, in addition to generator dropping, when pre-contingency flows are very high on the South of Napavine path.
9 Study Methodology Critical outage List N-1 Allston-Keeler 500kV line Keeler-Pearl 500kV lineN-2Double line loss of Paul-Allston and Paul-Napavine 500kV linesDouble line loss of Paul-Allston and Napavine-Allston 500kV linesLine fault and 500kV breaker failure contingency (4283) at Pearl (Keeler-Pearl-Ostrander 500kV)Line fault and 500kV breaker failure contingency (4394) at Keeler (Allston-Keeler-Pearl 500kV)Line fault and 500kV breaker failure contingency (4502) at Allston (Napavine-Allston-Keeler 500kV)Double line loss of Allston-Trojan #1 and #2 230kV linesDouble line loss of St.Marys-Trojan and Rivergate-Trojan 230kV lines
10 Generation pattern development Study MethodologyGeneration pattern developmentSouth of Napavine, South of Allston, and Keeler-Pearl path capacity varies with local load and generation patterns.BPA’s Operations typically operates the I-5 corridor within range of limits determined from studies where multiple generation patterns are considered.The study methodology exposes different problems occurring under different system conditions.The set of generators used in this study included existing plants and the following projects which affect the I-5 Corridor: Mint Farm, Grays Harbor, and Pacific Mountain Energy Center.
12 Study MethodologySCADA data was collected for the Willamette Valley/Southwest Washington load service area and Allston-Keeler 500kV line flows to determine generation patterns most likely to occur under peak load and high north to south flows.The most limiting generation patterns which are likely to occur during peak summer load conditions combined with high north to south flows through the I-5 corridor are:Patterns G0, G2, G5, G8, G16, and G24In these patterns, most of the I-5 Corridor generation was on-line.The conclusion is that most I-5 generation is on-line when the WILSWA area load is peaking in the summer and Allston-Keeler 500kV line flows are high.
14 Reliability Criteria / Planning Standards Study MethodologyReliability Criteria / Planning StandardsThermal Limit Criteria:All lines may not exceed their thermal limit for all conditions.Transformers may not exceed their thermal rating for all lines in service conditions and may not exceed their emergency rating under outage conditions.Voltage Limit Criteria:For all lines in service, maintain a minimum of 1.0 per unit voltage and 0.95 per unit or applicable voltage for outage conditions.Voltage Stability Methodology:Generation on low-side voltage controlCapacitor groups locked from switching (selected 500kV shunt capacitor groups were switched during the contingency)Transformer taps lockedSVCs allowed to adjustThe real power margin criteria were applied using the QV Analysis tool in Power World. QV curves were constructed at various transfer levels near a thermal limit scenario. The voltage stability limit was determined from the transfer or path flow level with zero margin.
15 Existing System Performance In the following analysis of the existing system performance, the peak summer 2008 base case loads were used. As a result of the future load levels used, the South of Napavine and the South of Allston path TTC determined from the studies is lower than the current posted TTC and less than the path capacity sold. This is due to the difference in how the TTC is determined between this planning study and the studies used to set operating limits.The posted TTC levels were set using a WECC summer 2005 operating case. In the operating case loads were modeled at 95 percent of peak. The operating studies model conditions more likely seen on the system during high north to south transfers.This planning study models peak future loads (2008) occurring simultaneously with high transfers. The local loads affect the flows along the I-5 Corridor and, thus, affect the internal path TTC. As a result, higher loads in the Portland and Vancouver load centers will reduce South of Napavine and South of Allston TTC, as this study shows.
16 I-5 Corridor Internal Paths Within the service area, four significant paths are monitored to ensure the system is operated within safe limits. These paths are described below:Raver-PaulRaver-Paul 500kV line rated at 2900Amp capacity, 30°C AmbientSouth of Napavine 500kVPaul-Allston #2 500kV line at 3260Amp capacity, 30°C AmbientNapavine-Allston (Paul-Allston #1) 500kV line at 3220Amp capacity, 30°C AmbientSouth of AllstonAllston-Keeler 500kV line at 3500Amp capacity, 30°C AmbientTrojan-St. Mary’s 230kV line at 1315Amp capacity, 30°C AmbientTrojan-Rivergate 230kV line at 1315Amp capacity, 30°C AmbientRoss-Lexington 230kV line at 1070Amp capacity, 30°C AmbientMerwin-St. John’s 115kV line at 673Amp capacity, 30°C AmbientAllston-St. Helens 115kV line at 850Amp capacity, 30°C AmbientAstoria-Seaside 115kV line at 502Amp capacity, 30°C AmbientKeeler-PearlKeeler-Pearl 500kV line at 2590Amp capacity, 30°C Ambient
18 South of Napavine PathLimiting Outage: The double line loss of Paul-Allston #1 and #2 500kV linesLimiting Elements:Chehalis-Longview #1 and #3 230kV linesHolcomb-Naselle 115kV lineExisting South of Napavine path limit MW (with 2700MW RAS gen drop)South of Napavine path limit from I-5 Corridor study resultsThermal limits: 1830MW (G27) – 2320MW (G2)Voltage Stability: 2600MW (G31) – 2760MW (G0) with SOCSS implemented
20 South of Allston PathLimiting Outage: Line fault and Keeler 500kV breaker 4394 failure outage causing the double line loss of the Allston-Keeler and Keeler-Pearl 500kV linesAdditional outages:Allston-Keeler 500kV line outageDouble line loss of Allston-Trojan #1 and #2 230kV linesLimiting Elements:Ross-Lexington 230kV line (will be upgraded in late 2007)St. Mary’s-Trojan 230kV line (PGE)Longview-Lexington #2 230kV lineHarborton-Rivergate 230kV line (PGE)Keeler-St. Mary’s 230kV line (PGE)Merwin-View 115kV line (PAC)Existing South of Allston path limit MW (with 2700MW RAS gen drop)
22 Keeler-PearlLimiting Outage: Line fault and Pearl 500kV breaker 4283 failure outage causing the double line loss of the Keeler-Pearl and Pearl-Ostrander 500kV linesAdditional outages:Keeler-Pearl 500kV line outageLine fault and Pearl 500kV breaker 4280 failure outage causing the loss of the Keeler-Pearl 500kV line and a Pearl 500/230kV transformerLimiting Elements:Keeler-St. Mary’s 230kV line (PGE)Keeler-Pearl is considered a sub path of the South of Allston and governed by the South of Allston limitSouth of Allston path limit from I-5 Corridor study resultsThermal limits: 2560MW (G27) – 3010MW (G2)
23 Existing System Performance Other lines requiring upgrades in the I-5 corridor to support load service and future generation interconnections:(BPA) Keeler-Forest Grove 115kV line(BPA) Allston-Rainier-Goble-St.Helens 115kV line(PAC) Astoria-Seaside-Cannon Beach 115kV line(BPA & CCP) Longview-Cardwell-Lexington 115kV loop(BPA) Keeler-St. Johns 115kV line(PGE) Orenco-Sunset 115kV line(PAC) St. Johns-Columbia 115kV line(PGE) Sherwood-Tualatin-Durham 115kV line
24 Existing System Performance Summary of Existing System PerformanceThe South of Napavine and South of Allston TTC range based on the load forecast and base cases used is 1830MW to 2310MW and 2560MW to 3010MW respectively. The voltage stability limit of the system, with SOCSS implemented, ranges from 2600MW to 2760MW.Under certain generation patterns the South of Allston path TTC may not be usable due to the voltage stability limit of the South of Napavine path, which is in series with it.Other thermal violations exist that are not directly transfer related, but are aggravated by load growth and new generation interconnections in the I-5 corridor.
25 Options Studied Upgrade Lower Voltage System This option includes rebuilding, re-conductoring, or re-sagging entire lines or sections of 230 and 115 kV lines in the I-5 Corridor (approximately 130 miles), so they can support the high transfers in the event of an outage of the main grid 500kV system. Some of the lower voltage facilities belong to other utilities which operate in parallel to BPA’s main grid transmission system. This alternative mitigates the thermal overloads. However, line upgrades do not mitigate the voltage instability problems identified.The following list only includes lines that require upgrades for increased transfers and does not include some generation interconnection and load service related facility upgradesThe plan of service for this alternative includes the following line upgrades:(BPA) Longview-Chehalis 230kV line from Longview to tap, 1976Amp capacity(PGE) Keeler-St.Marys 230kV line, 1836Amp capacity(PGE) St.Marys-Trojan 230kV line, 1387Amp capacity(BPA) Ross-Woodland 230kV line, 1358Amp capacity(BPA) Longview-Lexington #2 230kV line, 1101Amp capacity(PAC) Merwin-View-Cherry 115kV line, 992Amp capacity(PAC) Astoria-Seaside-Cannon Beach 115kV line, 535Amp capacity(BPA) Allston-Rainier-Goble-St. Helens 115kV line, 945Amp capacityThese are the minimum upgrades required, do not eliminate the SOCSS and assume any new generation is incorporated into existing RAS
26 Options Studied Upgrade Lower Voltage System To completely eliminate the SOCSS and utilize the full South of Allston path capacity for the worst case generation scenario (Pattern G27) the following line upgrades would also be needed:(BPA) Longview-Chehalis 230kV line from Longview to tap, 2982Amp capacity(BPA) Longview-Chehalis #3 230kV line, 1550Amp capacity(BPA) Longview-Chehalis #1 230kV line, 1441Amp capacity(BPA) Olympia-Chehalis 230kV line, 1438Amp capacity(BPA) Holcomb-Naselle 115kV line, 560Amp capacity(BPA) Cathlamet-Cathlamet tap 115kV line, 319Amp capacityThe alternative of upgrading the lower voltage system was not recommended due to the voltage stability performance of the system during the double line loss of Paul-Allston and Paul Napavine 500kV lines and the large number/mileage of line upgrades required to accommodate the new generation in the queue. Also, this alternative does not permit any reduction to RAS or improve voltage stability performance.
27 Options Studied Construct a New Paul-Pearl 500kV line Another alternative studied was a new Paul-Pearl 500kV line. A couple of routes for this line were considered.The Paul-Pearl 500kV line plan of service includes:Construct a new 500kV three breaker ring bus approximately 12 miles north of Allston substation (near Castle Rock, WA) tied into the Napavine-Allston 500kV line.This site was chosen to mitigate common corridor outages in the Paul-Allston transmission corridor.Construct a new Pearl 500kV bay to terminate the new 500kV lineMultiple routes are possible for the Paul-Pearl 500kV line:Construct approximately 100 miles of 500kV line from the new substation north of Allston toward the west side of the Portland/Vancouver load service area through Clatskanie, Timber, Carlton, and Sherwood substations to Pearl. This alternate route may require new right of way through forested areas.Construct approximately 80 miles of new 500kV line from the new substation north of Allston paralleling the Ross-Lexington 230kV, Ross-St. John’s 230kV, St. John’s-Keeler 115kV, and Keeler-Oregon City 115kV lines to Pearl substation. This alternate route uses existing right of way through Forest Park and Portland neighborhoods and may require rebuilding some of the adjacent lines to double circuit with the new 500kV line.Swap the Raver-Paul and Paul-Allston #1 500kV lines 2.6 miles from Paul substationThe line swap was necessary to mitigate common corridor outages in the Paul-Allston transmission corridor.
29 Options StudiedPaul-Pearl Plan of Service-ContinuedThe Paul-Pearl plan of service would require some additional line upgrades to maximize the paths’ increased capacityAdditional improvements identified:Upgrade the (PAC) Merwin-View-Cherry 115kV line to 1000Amp capacityUpgrade the (BPA) Allston-Rainier-Goble 115kV line to 900Amp capacityUpgrade the (BPA) Longview-Chehalis 230kV line from Longview to the tap, approximately 2 miles, to 2140Amp capacity.These additional improvements do not include load service and generation interconnection upgradesA new Paul-Pearl 500kV line was not recommended due to the potential for greater environmental impact, high cost of land through the city of Portland, and increased project cost due to a longer alternate route length. Overall, it is expected that this would be a more costly alternative than the recommended plan of service without significantly greater benefits.
30 Options StudiedConstruct a New Paul-Troutdale 500kV line – Recommended AlternativeThe Paul-Troutdale 500kV line plan of service includes:Construct a new 500kV three breaker ring bus approximately 12 miles north of Allston substation (near Castle Rock, WA) tied into the Napavine-Allston 500kV line.This site was chosen to mitigate common corridor outages in the Paul-Allston transmission corridor.Construct a 500kV three breaker ring bus at the Troutdale 500kV yardRe-terminate the Ostrander-Troutdale 500kV line and the Troutdale 500/230kV transformer into two of the new bay positions. The third bay position will be for the new 500kV line.Construct approximately 70 miles of new 500kV line from the new substation (north of Allston) to Troutdale.Swap the Raver-Paul and Paul-Allston #1 500kV lines 2.6 miles from Paul substationThe line swap was necessary to mitigate common corridor outages in the Paul-Allston transmission corridor.
32 Options Studied Paul-Troutdale Plan of Service - Continued The Paul-Troutdale plan of service would require some additional line upgrades to fully utilize the capacity of the new 500kV lineAdditional improvements which may be included in the plan of service:Upgrade (PAC) Troutdale-Gresham 230kV line, (PAC) Harrison-Lincoln 115kV line, and (PGE) Blue Lake 230/115kV transformerUpgrade (PAC) Merwin-View Tap-Cherry 115kV lineRe-terminate the Keeler-Pearl 500kV line into a new bay at PearlUpgrade the (BPA) Allston-Rainier-Goble 115kV lineUpgrade the (BPA) Longview-Chehalis 230kV line from Longview to the tap, approximately 2 miles, to 2140Amp capacity.These additional improvements do not include load service and generation interconnection upgradesWith the new Paul-Troutdale 500kV line, the “net” TTC increase (TTC increase minus the path flow increase) for the South of Napavine and South of Allston paths are approximately 545MW and 675MW respectively. Additional TTC increases can be achieved by the following:Upgrade the Longview to Longview tap line section to 2140Amp capacityRe-terminate the Keeler-Pearl 500kV line into a new 500kV bay at PearlUpgrade some additional lower voltage lines
33 Comparisons of Alternatives The Paul-Troutdale plan of service provides additional thermal capacity and system reactive support by providing a parallel path to the existing I-5 Corridor 500kV transmission system and also reduces system losses.The Paul-Troutdale plan of service also provides the potential to reduce dependence on RAS generation dropping.The Paul-Troutdale plan of service would accommodate proposed new generation in the interconnection queue.The Paul-Pearl plan of service would have similar performance to the Paul-Troutdale plan of service.The lower voltage upgrade plan of service would require approximately 130 total miles of line upgrades to accommodate the generation in the queue.The lower voltage upgrade plan of service would be expensive and does not enable any reduction in RAS.The lower voltage system upgrades would not reduce losses.Wide spread reactive additions would be required to support voltages in the event the SOCSS is implemented.Operating the system with higher amounts of switched capacitor groups could be difficult to coordinate.Without additional reactive support for the South of Napavine path, it would be unlikely the South of Allston path capacity could be fully utilized, since the paths are in series. Therefore it wouldn’t be possible to achieve the full benefit of the upgraded lines.
34 Recommended Plan of Service BPA’s recommended plan of service is to construct the Paul-Troutdale 500kV line.The new Paul-Troutdale 500kV line provides additional capacity to integrate new generation and accommodate new transmission requests into the I-5 Corridor and potentially reduce dependence on RAS.The new Paul-Pearl 500kV line was not recommended due to potential environmental impact, high land cost through the city of Portland, and higher project cost due to a longer alternate route length.The lower voltage system upgrades were not recommended due to inadequate voltage stability performance, continued dependence on existing RAS, and cost associated with the amount of lines needing upgradesCost estimates are being developed for the Paul-Troutdale 500kV line plan of service. Costs are anticipated to be in the range of $200M (based on previous estimates).