Avista Closes In on 230-kV System Upgrade

Jul 1, 2007 12:00 PM
By David James, Avista

Avista Utilities is wrapping up a five-year project to increase capacity and reliability of its 230-kV transmission system. Avista (Spokane, Washington, U.S.) finalized the infrastructure plan in August 2002 after many years of system-planning analysis and close coordination with a group of Northwestern transmission stakeholders that included the Bonneville Power Administration (BPA; Portland, Oregon, U.S.). The plan involves adding nearly 100 circuit miles (161 km) of 230-kV transmission line and upgrading the capacity on another 50 miles (80 km). Avista also added two transmission substations and reconstructed three existing stations.

In total, Avista will perform upgrade work at 12 of its 13 230-kV substations. The utility opted to install nearly 200 miles (322 km) of fiber-optic cable to control, monitor and protect its investment. That system also will enable a new remedial action scheme to allow better coordination between hydro resources and transmission capacity.

BEACON-RATHDRUM TRANSMISSION LINE

A major portion of Avista's electric service territory involves two cities: Coeur d' Alene, Idaho, U.S. and Spokane. The original 230-kV link between the cities was constructed in the early 1950s and was rapidly reaching capacity limits. In the upgrade, Avista constructed a double-circuit 2000-MVA transmission line — the largest capacity line in Avista's history. The utility also reconstructed the Rathdrum station to a double-breaker, double-bus configuration, representing Avista's first fully redundant 230-kV substation. The transmission line and substation were commissioned in April 2004.

Avista's Beacon-Rathdrum circuit is electrically parallel to BPA's Taft-Bell 500-kV transmission line. Previously, outages on the 500-kV circuit created severe overloads on Avista's parallel path transmission line. To increase the capacity, Avista selected 1590-kcmil ACSS “Lapwing” conductor from Southwire. The 200°C (392°F) conductor design resulted in a capacity rating of 2000 MVA for the double-circuit line, a substantial increase over the 350 MVA single-circuit line constructed in the early 1950s. However, for these transmission line capacities to be fully realized, Avista significantly upgraded substation line position equipment to support the additional line loading. In some cases, line position ampacities were increased from 1600 to 3000 A through upgrades to equipment disconnects, power circuit breakers, larger main bus and line position terminal bus equipment.

At Rathdrum substation, issues related to a main bus outage and/or equipment failure led Avista to convert its main/auxiliary bus 230-kV station into a full double-breaker/double-bus configuration. In a double-breaker/double-bus scheme, a failure in a single piece of equipment is isolated to a single main bus, while the remaining bus stays in service. Not only does the topology guard against loss of service due to forced outages, the station design allows more flexibility when planning maintenance outages.

In conjunction with changes to the physical configuration of the station, design engineers matched the upgraded design with the latest protective relay and communication equipment combining Schweitzer Engineering Laboratory's (SEL; Pullman, Washington) 421 and 311L relays to provide redundancy in both design form and operational function. The combination of digital impedance and current differential relays implemented at Rathdrum has become Avista's standard design for 230- kV transmission lines.

GREENFIELD SUBSTATIONS

Following the success of the Beacon-Rathdrum project, Avista constructed two greenfield substations in Clarkston and Spokane Valley, Washington. The Dry Creek 230-kV substation, which was commissioned in June 2005, included a 200-MVAR shunt-capacitor bank supplied by Cooper Industries (Milwaukee, Wisconsin, U.S.). Avista operates 400 MVAR of shunt-reactive compensation on its 115-kV system. The installation at Dry Creek, however, was the first installation at 230 kV and represented a 50% increase in the company's reactive supply. Each 67-MVAR capacitor-bank segment is connected to an asynchronous Mitsubishi power circuit breaker. At 115 kV, Avista had used circuit switchers with pre-insertion devices to mitigate switching transients, but chose to employ the zero-crossing breakers at Dry Creek.

The Dry Creek substation was Avista's first greenfield 230-kV substation since the early 1980s. Faced with the task of developing several hundred engineering drawings, the company elected to partner with Electrical Consultants Inc. (ECI; Billings, Montana, U.S.), which later assisted with the design of the Boulder substation in Spokane Valley.

COMMUNITY COLLABORATION

Prior to the commissioning of Dry Creek, ground-breaking occurred at the Boulder substation. Commissioned in October of 2005, Boulder is Avista's second-largest 230/115-kV substation supporting nine area transmission lines and integrating 500 MVA of 230/115-kV transformation capability from VA TECH Ferranti-Packard de Mexico, S.A. de C.V. However, the uniqueness of Boulder is not the number of transmission lines connected, the station's capacity or new technology employed, but the public process that created the project.

In 2003, Avista sponsored a series of community workshops to explain the need for and solicit comments to expand the company's nearby Otis Orchards 115-kV substation. Over the course of the weekly sessions, the utility gathered stakeholder input and created a series of project alternatives such as developing a new site near the Boulder generating station, a small gas-fired generating plant constructed in 2002. Avista discussed and evaluated many community-sponsored options including under-grounding portions of existing 115-kV transmission lines. But in the end, the “Boulder option” gained overwhelming public support and was embraced by the company for its strategic location near existing 230-kV lines.

Public involvement is not new to either Avista or the utility sector; however, the company recognized the constructability of the Boulder option along with other operational and reliability advantages. In turn, the community worked collaboratively with the utility during the permitting and rights-of-way acquisition phases of the project.

PALOUSE 230-KV UPGRADE

The most ambitious component of Avista's plan is a US$54 million investment involving the construction of a 60-mile (97-km) 230-kV transmission line through the heart of Washington's Palouse farm country. The line will connect the urban load centers of Avista's system. Following a three-year period of siting, permitting, design and material acquisition, Avista broke ground in April 2006 on the transmission line with International Line Builders (ILB; Portland, Oregon, U.S.) and its foundation subcontractor Tri-State Drilling.

During the first year of construction, ILB installed more than 200 self-supporting tubular-steel structures from Valmont Industries Inc. (Omaha, Nebraska, U.S.), which supplied 100% of the steel structures used by Avista during the 230-kV upgrade initiative. As worldwide demand for steel increased in the years following 2003, Avista forged an alliance with Valmont to allow more flexibility in Valmont's production schedule, and to base the cost of finished products on the combination of fixed labor costs plus the incremental costs of raw steel. By sharing the risk of steel cost escalation between Avista and Valmont, both companies were able to achieve a lower-cost product.

In addition to the supply-side alliance, design consultants POWER Engineers (Hailey, Idaho) developed a series of cost-containment measures, including the use of braced-line post structures in lieu of steel poles with davit arms. By eliminating the need for steel davit arms on tangent structures, the utility saved more than $1 million. POWER Engineers used a computer-aided design from Pondera (Spokane) to spot the towers over the 60-mile line route. Since its first use in 2004 on the Palouse line, Avista has integrated Pondera's software into its regular design process. Computerized design allows the project engineer flexibility when evaluating route options during preliminary design and provides the necessary horsepower to rapidly prepare the final design, specify materials and establish construction standards.

In the spring of 2007, Avista began construction on the remaining 26-mile (42-km) line segment from Rosalia, Washington, to the Benewah substation. The line is expected to be operational by the end of November 2007 and will mark the end of Avista's $130 million effort to upgrade its 230-kV transmission infrastructure.

David James earned his BSEE degree from the University of Idaho, his MSEE degree from Washington State University and completed a project management certificate program from Washington State. He has worked for Avista since 1991 both in transmission design and operations. Most recently, he served as the project manager for Avista's 230-kV upgrade project and now serves as the company's transmission design manager. dave.james@avistacorp.com

Avista is installing nearly 200 miles of fiber-optic control cable to support the protection and communication control of newly added transmission circuits and substation facilities and to meet NERC reliability standards. A remedial action scheme will be implemented to control generation on the Clark Fork River. Avista is using digital radio communication to avoid stringing fiber lines through mountainous terrain. The utility used optical ground wire on new steel tower lines, together with all-dielectric, self-supporting fiber cable on existing wood-frame transmission lines.