Completed for Transmission Customer Proposed Resource & Transmission Carbon County, MT & 230 kv Transmission in North Wyoming August 2016
Table of Contents 1.0 Description... 1 2.0 Overall Assumptions... 1 3.0 Study Results... 2 4.0 Conclusions... 4 Transmission Customer i August 2016
1.0 Description Transmission Customer and PacifiCorp Transmission are parties to a Transmission Consulting Study Agreement ( Agreement ). The Agreement allows for Transmission Customer to engage PacifiCorp Transmission for transmission planning consulting services where PacifiCorp shall act as Transmission Customer s consultant to evaluate specific study requests submitted from time to time by Transmission Customer, and provide high level descriptions and general cost estimates of facility requirements, for possible Network Resource designations or terminations. In accordance with Section 2 of the Agreement, Transmission Customer submitted a written request for study. This study report evaluates the Transmission Provider s main grid system to identify any system constraints in order to supply the requested service for the following request: Transmission Customer requests that PacifiCorp Transmission include in its study report a complete examination of Transmission Customer s planning redispatch options (and any associated costs) under the Network Operating Agreement (NOA) between Transmission Customer and PacifiCorp Transmission, Section 8.1, Planning Redispatch Procedures. Transmission Customer also requests that PacifiCorp Transmission study three (3) different planning redispatch alternatives: 1. Redispatch with all three projects (240 MW total). a. Pryor Caves Wind Project, LLC (80 MW) b. Mud Springs Wind Project, LLC (80 MW) c. Horse Thief Wind Project, LLC (80 MW) 2. Redispatch with only two projects, Pryor Caves and Horse Thief (160 MW total). 3. Redispatch with only one project, Pryor Caves (80 MW total). PacifiCorp Transmission has performed the study considering the three (3) different planning redispatch alternatives mentioned above and the study findings are described in Section 3. 2.0 Overall Assumptions Mentioned below are some assumptions that were used for the study and are common for all three redispatch alternatives that were studied. The three new wind resources located in Carbon County, Montana are interconnecting to the same Point of Interconnection (POI) on PacifiCorp s transmission system. The new resources are interconnected on the 230 kv line between Yellowtail and Frannie delivering project output to Frannie. Transmission Customer 1 of 5 August 2016
For all three alternatives, a conventional resource (thermal) in eastern Wyoming was commensurately backed down in order to accommodate these new resources. All three projects were assumed to have the Gamesa G114 2.0 MW wind turbines. Only existing resources and resources with transmission service requests in that area were considered for this study. Resources that are currently in PacifiCorp s Generation Interconnection Queue that are neither designated network resources nor have a transmission service request were not considered in the study. All facilities will meet or exceed the minimum Western Electricity Coordinating Council ( WECC ), North American Electric Reliability Corporation ( NERC ), and the Transmission Provider s performance and design standards. All existing and proposed Remedial Action Schemes (RAS) are assumed to be in service for this study. A synchronous condenser at Standpipe Substation is assumed to be in service for this study. The following power factor requirement was assumed for the Project: 9.6.1 Power Factor Design Criteria. Interconnection Customer shall design the Large Generating Facility to maintain a composite power delivery at continuous rated power output at the Point of Interconnection at a power factor within the range of 0.95 leading to 0.95 lagging, unless Transmission Provider has established different requirements that apply to all generators in the Control Area on a comparable basis. Non-synchronous generators shall only be required to maintain the above power factor when their output is above 10 percent of the Generating Facility Capacity. 3.0 Study Results A Western Electricity Coordinating Council (WECC) approved 2016 Heavy Summer operating case modified to represent the 2017 heavy load conditions and a 2018 Light load conditions case were used to perform the power flow studies using PSS/E version 33.7. Power flow studies were performed on both peak and off-peak load cases. The off-peak load case was chosen to demonstrate the stress on the higher kv transmission system under light load conditions. Based on the location of the interconnection, the three proposed projects would be considered on the north side of the Yellowtail South (YTS) cutplane and would have to cross this cutplane in order to serve network load. The YTS is defined as follows: (1) Yellowtail (PacifiCorp) Frannie 230 kv line (measured at Yellowtail) (2) Yellowtail (PacifiCorp) Goose Creek 230 kv line (measured at Yellowtail) (3) Yellowtail (WAPA) Lovell 115 kv #1 line (measured at Yellowtail) Transmission Customer 2 of 5 August 2016
(4) Yellowtail (WAPA) Lovell 115 kv # 2 line (measured at Yellowtail) The definition of the YTS cutplane may change with the interconnection of the proposed projects. YTS is operated by Western Area Power Administration (WAPA) and the capacity across this cutplane is shared among PacifiCorp and WAPA. WAPA also has established a nomogram between Yellowtail generation and YTS operating limit. The interconnection of any of these three projects may trigger a restudy and a new nomogram may need to be developed to determine the new operating limits in coordination with WAPA. The proposed projects will have to use the TOT4A path as well in order to serve the network load and the firm capacity across this cutplane is fully subscribed. TOT4A path is defined below: (1) Standpipe Platte 230 kv line (measured at Standpipe) (2) Mustang Spence 230 kv line (measured at Spence) (3) Riverton Wyopo 230 kv line (measured at Riverton) If additional capacity on TOT4A path is requested then new transmission will be required in order to increase capacity across this path. The local 230 kv and 115 kv transmission system outages were considered during the study. The results of the individual redispatch alternatives studied are explained below. Alternative 1) Redispatch with all three projects (240 MW) For this alternative, all three projects (Pryor Caves, Mud Springs & Horse Thief) were redispatched. The flows across the Billings Steam Plant 230 kv phase shifter, Crossover 230 kv phase shifter and Rimrock 161 kv phase shifters were adjusted in order to ensure that flows across YTS are not exceeded. A 240 MW resource in the area was redispatched, keeping the flows across TOT4A below its limit. Several local area contingencies were studied on both a peak and off-peak case in order to determine the impacts of the addition of all three projects. The thermal overloads and low voltages observed for this scenario are shown in Table 1 below: Table 1: Thermal Overloads and Voltage Issues Thermal Overloads Contingency Overloaded Element Overload in Peak Case (%) Overload in off-peak Case (%) POI Oregon Basin Basin Nahne Jensen 103 N/A 230 kv line 115 kv line (WAPA owned) Low Voltages Contingency Low Voltage Bus Voltage (PU) in Peak Case Voltage (PU) in Offpeak Case Transmission Customer 3 of 5 August 2016
POI Oregon Basin 230 kv line Nahne Jensen 115 kv 0.887 N/A Greybull 115 kv 0.894 N/A Basin 115 kv 0.895 N/A A Remedial Action Scheme (RAS) will be required to alleviate the overload on the Basin Nahne Jensen 115 kv line for the outage of the POI Oregon Basin 230 kv line until WAPA performs a planned reconductoring of the Worland Tap Basin Nahne Jensen 115 kv line; the exact timing of the reconductoring is not known but is anticipated in the five year range. The RAS will monitor the thermal loading on the Lovell Nahne Jensen Basin Worland Tap 115 kv line and will curtail the wind generation due to overload for the outage of POI Oregon Basin 230 kv. This RAS will be temporary until the reconductoring of the line is completed. The high level non-binding cost estimate for this RAS is $1,000,000. No additional thermal overloads or voltage issues were observed for the local area contingencies that were studied. Alternative 2) Redispatch with only two projects, Pryor Caves and Horse Thief (160 MW total) For this alternative, two of the three projects (Pryor Caves & Horse Thief) were redispatched. The flows across the Billings Steam Plant 230 kv phase shifter, Crossover 230 kv phase shifter and Rimrock 161 kv phase shifters were kept similar to Alternative 1. The flows across YTS are slightly reduced due to a reduction in wind generation north of the cutplane. A 160 MW resource was also redispatched, keeping the flows across TOT4A below its limit. Several local area contingencies were studied on both a peak and off-peak case in order to determine the impacts of the addition of these two projects. No thermal overloads and voltage issues were observed for the contingencies studied. Alternative 3) Redispatch with only one project, Pryor Caves (80 MW total). For this alternative, only one of the three projects (Pryor Caves) was redispatched. The flows across the Montana Southeast path were kept similar to Alternative 1. The flows across YTS are reduced due to a reduction in the wind generation north of the cutplane. A generation resource was also redispatched by 80 MW, keeping the flows across TOT4A below its limit. Several local area contingencies were studied on both a peak and off-peak case in order to determine the impacts of addition of these two projects. No thermal overloads and voltage issues were observed for the contingencies studied. 4.0 Conclusions The planning redispatch options were studied for the three proposed projects (1) Pryor Caves Wind, LLC (2) Mud Springs Wind, LLC & (3) Horse Thief Wind, LLC in three different alternatives as described earlier. Transmission Customer 4 of 5 August 2016
Considering the Transmission Customer will manage its resources to stay within existing transmission rights across TOT4A path and YTS cutplanes by redispatching resources in the area, the study for Alternative 1 (240 MW) showed thermal overloads on WAPA s 115 kv transmission line between Lovell and Worland Tap. WAPA is planning to reconductor this 115 kv line in the next five years. Until WAPA performs the reconductoring, a RAS to trip a portion of the generation will be required to alleviate the overloads. Alternatives 2 (160 MW) and 3 (80 MW) did not show any thermal overloads or voltage issues for the local area 230 kv and 115 kv contingencies that were studied. Irrespective of the Alternative chosen to interconnect, coordination with WAPA will be required in order to determine the new operating limits and develop new nomogram for the YTS cutplane that includes the new proposed wind generation. Additional transmission in form of Gateway is required in order to increase capacity across TOT4A and Bridger West in order to serve network load if additional capacity is required across TOT4A to serve network load. Transmission Customer 5 of 5 August 2016