525-kV Self-Contained Oil-Filled Cable Systems for Grand Coulee Third Powerplant Design and Development

The more important requirements, and the design features developed to meet these requirements, are discussed in detail for the first three 525-kV oil-filled underground cable systems to be installed for the transformer circuits at Grand Coulee Third Powerplant. The cable systems will bq of the self-contained type and will be energized in 1974, the first at this voltage for commercial operation in the U.S.A. Consideration of unusual parameters such as the 600 feet (183 meters) elevation difference between terminals, installation in a 6-foot (1.83-m) wide tunnel, ambient temperature range from minus 27°C to plus 45°C, 1,800-kV cable B.I.L., along with insulation and accessory requirements for 525 kV, provided many unique design features that will be applicable to other similar projects, in addition to those with less stringent requirements.