Retrofitting Allis-Chalmers AIS switchgear
02/01/2004 - Volume I - Issue I
Case study: switchgear upgrade minimizes down-time, boosts substation uptime transfer capacity at Boeing
When you are reworking the electrical supply structure of a facility the size of Boeing's Everett District in Washington, a shutdown is inevitable. Boeing's Everett plant, the largest enclosed space in the world, produces the 747, 767, and 777 twin aisle airplanes. The total energy usage for the site is approximately 60 megawatts, and this energy is supplied through an infrastructure that consists of three 115,000 volt lines from the local utility, feeding three 40MVA, 115KV-to-12.47KV primary substations, and subsequently 214 individual 480 volt secondary substations.
When the main substation was originally designed, the main transformers were rated 28MVA and the site was manufacturing one airplane model. Boeing now has increased the transformer capacities to 40MVA and is manufacturing three additional airplane models. With production rising and the company installing more machine tools and computers to support the increased activity, it became clear that the load on the 2000 amp-rated buses as rapidly approaching the maximum rating of the 1200 amp bus tie.
Typical air-magnetic breakers
Every 1000 / 2000 operations
- Visual inspection
- Megger / hi-pot
- Measure / adjuct arc contacts
- Measure / adjust main contacts
- Check hinge / pivot arms
- Arc chute inspection and arc residue removal
- Check puffer bellows and tubes
- Significant lubrication
- Speed / motion timing
- Power factor testing
- Hi-pot testing
- Operational testing
1-2 men, > 8 hours
Siemens 3AF / 3AH vacuum breakers
Every 10 years or 10,000 operations
- Visual inspection
- Go / no-go erosion
- Dry cloth wipe down
- Minor lubrication
- Vacuum check
- Hi-pot testing
- 'Ductor' test
- Operation testing
1 man, < 4 hours
Under normal conditions, the existing configuration can supply the entire Boeing Everett site, but increasing the tie bus capacity to 2000 amps and the tiebreaker rating to 750MVA has a number of advantages. In an emergency, the plant would be able to operate the main substation with all main circuit breakers and tie breakers closed in order to seamlessly switch from one main transformer to another or remove one main transformer from service. This would prevent having to perform open transition switching and/or load shedding. The same outage required to perform the bus tie and tie-breaker upgrade would also provide the conditions to upgrade the main and branch breakers from 26 30-year-old Allis-Chalmers 15FCV 500-1200 air breakers to new, more reliable, Siemens 15 FSV 750-1200/2000 vacuum breakers. After studying the options, we decided on a dual approach: upgrade the tie bus to 2000 amps and replace all of the old 500MVA air breakers with 750MVA vacuum breakers. Although this was technically the best option for upgrading the substation, it required a site-wide electrical shutdown. A shutdown of this size had not been attempted in 25 years.
To accomplish the upgrade, a strategy to minimize downtime and a technical partner who could provide the on-site factory expertise and experienced field service personnel was essential. After some discussion with production management, Boeing scheduled 10 hours of downtime on Thanksgiving Day, 1998. Allis-Chalmers, a company now owned by Siemens, manufactured the existing switchgear, so it seemed prudent to purchase the equipment from Siemens and minimize interference and interface problems. Boeing had previous positive experiences with Siemens sales and field service personnel. After some discussion, Siemens assured Boeing that the equipment could be shipped in a timely manner to support its schedule. The companies then brainstormed the potential risks and the necessary mitigation, as a design-build partnership, so as to reduce communication breakdowns.
The planned shutdown also proved a welcome event for the Everett plant's electric utility company, as the manufacturing schedule provided no opportunities for the utility to perform with yard maintenance. They would piggyback on the outage and perform transformer and breaker testing on the utility-owned infrastructure supplying power to the plant.
By spring of 1998, Boeing gained full approval of a plan to have Siemens and a local sub-contractor install the new bus tie. As the time for installation approached, the pace of preparations gained momentum. In early November, the components arrived at the Everett site. Siemens verified completeness, dimensions, and quality of each delivery before Boeing staged the material near the substation.
The main power was taken out of service at 7 a.m. via the 115KV breakers, and the public utility linemen and Boeing electricians proceeded to clear all equipment and install safety grounders. Work commenced at approximately 7:30 a.m. When the existing bus tie and duct were disconnected, a Boeing crane lifted the new bus assembly from a flat bed trailer onto the roof of the main substation. By 4:45 p.m., the new bus tie, tiebreaker bottles, tiebreaker, and main breakers were installed and tested. Personnel grounds on the Boeing and utility sides were lifted and clearance tags were removed. At 5:30 p.m., the 115KV breakers were closed and the process of systematically energizing the site began. Fortunately, concerns about possible disturbances to the programmable plant equipment that had not gone through a stop cycle proved to be largely unwarranted. Electricians and operations personnel quickly returned equipment to operational mode in preparation for the third shift coming back to work that evening.
The substation upgrade represented a convergence of good planning, careful engineering, and a competent contractor with proven ability to complete a job in the face of challenging time constraints.