THE EXISTING AIR-INSULATED SWITCH RACK AT THE GRAYSON POWER PLANT DID NOT HAVE THE CAPACITY FOR EXPECTED NORMAL LOAD GROWTH and it occupied a lot of precious real estate. Furthermore, there were other expansion projects, including new generation, that would strain the capabilities of the facility.

The solution to these and other problems was found with the installation of a modern gas-insulated switchgear (GIS) station at Glendale Water & Power (GWP; Glendale, California, U.S.), a municipal-owned utility. The new GIS project took 21 months to complete at a cost of approximately US$20 million. The project was finished under budget and two weeks ahead of the scheduled completion date.

EXISTING SITE

The new GIS station, with its associated disconnect switches, ground switches, control house and other equipment, was constructed in a 150-ft by 65-ft (46-m by 20-m) area. It replaces a nonsectionalized air-insulated 69-kV switch rack at GWP's Grayson Power Plant, which occupied a 70-ft by 205-ft (21-m by 62-m) space for nearly 34 years. The new station saves 4600 sq ft (427 sq m) of valuable land that can be used for future expansion of GWP's electrical distribution system or new generators.

The new compact GIS system has the required interruption capacity of breakers and will provide the flexibility to meet the growing power demands of Glendale. In addition to occupying less space, it provides less visual impact, because it is a height of 8 ft (2.4 m) compared to the 25-ft (7.6 m) height of the old air-insulated station.

NEW STATION

The new GIS station has 17 69-kV bays of double-breaker and breaker-and-a-half arrangements on two 3150-A double buses. The buses can be sectionalized using two 3000-A circuit breakers. In all, the GIS consists of 42 circuit breakers that serve GWP's Grayson Power Plant, Air Way Switching Station and four distribution substations. Spare positions can be used to interconnect with future generation or a new distribution substation.

The GIS project was a turnkey design-build contract. ABB Inc. (Zurich, Switzerland), the primary contractor, provided the engineering and construction design and supplied the GIS station. The GIS station was fabricated in Germany, then assembled and installed at GWP. ABB subcontracted with Henkels & McCoy Inc. (H&M; Blue Bell, Pennsylvania, U.S.) for the civil construction and power-line work, and with Miron Electric (Chatsworth, California, U.S.) for the supervisory and control wiring of the GIS station.

The three organizations — ABB, H&M and Miron Electric — worked closely together with GWP to coordinate the schedule to avoid interrupting services during cutover periods. It was critical to the schedule that the cutover of the 69-kV circuits be completed before the summer peak load to maintain the n-1 reliability criteria. Through a cooperative effort, the project was completed without any interruption of service and on-time to meet GWP's new peak load record of 336 MW. The GIS station operated adequately without any glitches during the unprecedented heat wave in July 2006, with sustained temperatures reaching highs of 112°F (44°C).

CONSTRUCTION

The project, just like any large construction project, encountered a few major challenges, but they did not delay the project. As a result of effective project management and cooperative teamwork, the challenges were overcome by working the plan and timely decision making.

The first challenge was in the substructure construction work. The conduit duct bank was originally engineered using a trench that was 16.4 ft (5 m) wide and 2.6 ft (0.8 m) deep, 4 ft (1.2 m) below natural grade. It was designed to spread all conduits horizontally with the concept of intercepting 21 existing conduits for seven 69-kV lines located in close proximity to other existing 69-kV underground substructure and other utilities in the vicinity of the work.

The field construction personnel encountered difficulties because of existing sandy soil conditions, which required supporting the existing underground duct bank that contained several medium-voltage energized circuits, plus a nearby reclaimed water pipe. Electrical service could not be interrupted; therefore, the crews had to work near the energized cables during construction. H&M suggested redesigning the single big-duct bank with two separate smaller-duct banks that are 3 ft (0.9 m) wide and have a maximum depth of 10.5 ft (3.2 m). This change made it more practical to intercept the existing conduits and facilitate the installation of the new cables for cutover to the existing circuit. The only time the power cables needed to be de-energized was during the actual interception work to interconnect existing circuits to the new GIS station. Only those circuits being worked on were de-energized, keeping the other circuits energized to meet the system's reliability requirements. Special excavation, support and shoring methods were used to protect existing substructure.

There were three 69-kV 1500 MCM Al power cables coming from Grayson Power Plant, three 69-kV paralleled 2000 MCM Cu cable lines coming from the 230-kV Air Way Switching Station, two 69-kV 1500 MCM cable lines going to the two tie transformers for 69 kV to 34.5 kV at the Glendale Switch Rack and eight 69-kV 1500 MCM cable lines going to the distribution substations at Western, Rossmoyne, Columbus and Tropico. All of these cables had to be rerouted without interruption of service and not affect GWP's power import and export. Rerouting of these 16 69-kV lines required close coordination between the GWP, ABB and H&M project team.

The 69-kV cables required specially made terminators for installation in the GIS and were supplied by ABB. H&M field personnel were specifically trained to prepare the cables, construct the terminators and install the assembly inside the GIS. H&M's construction personnel's experience in cable terminations and installations allowed them to pull, terminate, install, commission and test all cable without any difficulties.

TEAMWORK

Proper coordination between GWP and H&M resulted in 21 existing conduits for seven 69-kV circuits being intercepted and rerouted without undermining reliability of the energized electrical system. This teamwork also made it possible for the cutover to move forward in a rapid, safe and efficient manner, in spite of having to schedule cutovers to conform to GWP's reliability requirements.

The new GIS station provides GWP more reliability and flexibility in the operation of its electrical system. The sectionalized double bus provides improved flexibility to switch and isolate circuits for maintenance. The new relays and other intelligent electronic devices provide endless capabilities to collect data for analysis during system anomalies. Pilot wire relays were upgraded to use GWP's fiber-optic system.

The project started on Aug. 18, 2004, with completion originally targeted for summer 2006 to ensure that the electric system would be able to provide for the summer peak load, as GWP is a summer-peaking utility. The contract between GWP and ABB required that the project be completed before June 2006 to maintain a reliable system during the summer. Assembly of the new system was completed in January 2006, which allowed five months of cabling work to transfer the interconnection from the air-insulated switchgear to the new GIS, plus the testing and commissioning of the system in its entirety. The project was completed early, on May 16, 2006.

The final cost of the project was $18.7 million, which was below the budgeted $19.8 million. Completing a project this size on schedule and under budget was a major accomplishment. This was made possible through good project planning by GWP, overall good project management and a thorough understanding of project goals and existing site conditions by ABB, the field experience and creativity by H&M, and excellent teamwork by all parties.

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Ramon Abueg is the electrical services administrator for Glendale Water & Power. Abueg holds a BS degree in electrical and electronics engineering from California State University Sacramento and a MBA degree from Woodbury University. He is a registered professional electrical engineer in the state of California. rabueg@ci.glendale.ca.us