In March 1995, Tampa Electric Co., Tampa, Florida, U.S., signed a bulk power contract with Reedy Creek Improvement District (RCID). Reedy Creek Energy Services, under contract to RCID, provides nine utility services, including electricity, water and sewer services, to the 33,000-acre (133.5-km2) Walt Disney World complex in Orlando, Florida. As part of the contract, Tampa Electric agreed to construct a 230/69-kV substation in Osceola county and install 4.3 miles (6.9 km) of underground 69-kV transmission line to interconnect the new substation with Reedy Creek's existing Studio Substation at Disney-MGM Studios.
To provide a direct power source into the new substation, Tampa Electric purchased 25% capacity of the existing 230-kV Taft-McIntosh transmission line in central Florida owned by Orlando Utilities Commission. The 25% capacity purchased is the equivalent of 111 MW.
A Substation Takes Shape The Osceola Substation posed some unique engineering challenges because it is positioned on a long, narrow 4-acre (0.0162-km2) piece of property owned by Walt Disney World. The substation consists of two 230-kV circuits terminated on a ring bus, one 230/69-kV, 224 MVA autotransformer and one 69-kV underground circuit to the Studio Substation (Fig. 2) with a design for future expansion (Fig. 3). The unusual shape of the site prohibited a traditional layout, and it was necessary to provide for an extension of the future 69-kV bus from the north end to the south end by using underground cable. The initial 69-kV circuit, as well as all future 69-kV circuits, uses underground cable with very low impedance, which, combined with the high available fault current at the substation, requires current-limiting reactors on all 69-kV circuits in the station.
A necessary half-acre stormwater retention pond also limited equipment layout on the site. The substation is sloped from north to south to drain rainwater toward the pond, where it is then naturally filtered of sediment and surface debris before being released to an adjacent wetland area. In addition, since the autotransformer is filled with insulating fluid, safeguards were needed to prevent environmental damage in the event of a fluid leak.
A concrete pit, 10 ft (3.1 m) deep, was installed surrounding the transformer and was designed to contain the transformer's total fluid volume plus any rainwater that might accumulate. Under normal conditions, submersible pumps keep rainwater pumped out of the pit and into the stormwater system. Sensors in the pit automatically shut off the pumps and send an alarm to Tampa Electric's Energy Control Center if insulating fluid is detected in the pit. To minimize the visual impact of the substation, Tampa Electric built a 4 ft (1.2 m) high berm around the site and planted more than 1200 plants and 160 trees to enhance its appearance.
The 230/69-kV autotransformer, manufactured by Ferranti-Packard Transformers, Inc., St. Catherines, Canada, was transported by train to a rail siding in Kissimmee, Florida. At the rail siding, the transformer, which is 15 ft (4.6 m) high and weighs 285,000 lbs (129,274 kg), was loaded on a special 215 ft (65.5 m) long tractor trailer and moved about 20 miles (32.2 km) to a point where it had to cross the median of U.S. Highway 192, the main highway leading to Walt Disney World. The grass median had to be built up and leveled, then restored to its original condition after the move. Traffic was blocked in both directions for about two hours to accommodate the oversize rig. Crews faced some anxious moments when the transformer passed under a highway overpass, with only 4 inches (102 mm) to spare.
Going Underground While construction of the substation took shape above ground, 4.3 miles (6.9 km) of 69-kV transmis-sion line were installed underground, along World Drive, the main entrance into Walt Disney World. The southerly 2 miles of the route pass through Florida flatwoods, which are slated for future roadway expansion, while the northerly 2 miles (3.2 km) of the route run along the existing right-of-way (R/W) of World Drive including 1.6 miles (2.6 km) in the median of the divided highway. The remaining 1000 ft (304.8 m) were located in the back lot of Disney-MGM Studios.
Tampa Electric hired the design and construction management firm Black & Veatch, Kansas City, Missouri, U.S., to oversee the cable installation project. Bids solicited for the cable resulted in the selection of a 1500-kcmil (760-sq-mm) copper, 600-mil EPR-insulated solid dielectric cable with a continuous rating of 1200A, which was manufactured by Kerite Co., Seymour, Connecticut, U.S. In a separate competitive-bid process, UTEC Constructors of Topsfield, Massachusetts, U.S., was selected as the prime contractor for the underground project.
Environmental permits were coordinated by Tampa Electric's Environmental Planning Department. Heidt & Associates, Tampa, prepared a detailed environmental package, which was quickly approved by the appropriate agencies. A permitting process that normally takes six months was completed in just 90 days. Inclement weather soon became another challenge in the project. When construction was ready to begin, near-record rainfalls occurred. As a result, crews used the sock method to rid excess water from the southerly 2 miles (3.2 km) of the construction route (Fig. 4). With this dewatering method, perforated flexible pipe is covered with cloth and inserted 9 ft (2.7 m) underground along the trench route. Large pumps are then located to draw water for 1500 ft (457 m) in either direction. This method costs half as much as traditional well-pointing methods.
Workers cleared nearly 2 miles of land while simultaneously installing the direct-buried cable. Also installed in the trench was a fiber optic communication cable in 2-inch (51-mm) polyvinyl chloride (PVC) duct. A concrete cap protects the line in the direct-buried portions. Eight directional drills were required along the route, totaling 2500-circuit ft (762-circuit m). Each drill consisted of four 6-inch (152 mm) high den-sity polyethylene (HDPE) flexible pipes. Crews drilled under four wetland areas and under four major road crossings. The longest was a 400-ft (122 m) section under wetlands. Drilling proceeded smoothly, averaging one pipe per day (Fig. 5).
With Walt Disney World attracting thousands of visitors a day, it was vital that construction not interfere with normal operations of the theme park. Since nearly 2 miles of the route were located in the median of World Drive, crews planned construction to coincide with times when traffic into the complex was lightest. Crews exercised extreme care not to damage existing utility lines that could interrupt service and to replace sod and landscaping in the R/W as quickly as possible. A 200-ft (61-m) section of cable had to be installed in a 3-ft-wide (0.9 m) area adjacent to the pavement to skirt the bridge abutments of the Osceola Parkway overpass. The entire installation process took nearly four months to complete. Successful cable termination and hi-pot testing were done in February 1996.
Designing a Landmark Tower The concept of a unique 230-kV transmission pole came from Disney artists, who produced a computer-generated picture of a pole in the shape of the world's most famous mouse. The pole would be installed near the new substation. The original picture showed a tangent structure, but the layout of the station required the mousehead pole to be a self-supporting, double dead-end structure. The location of the new substation coincided with the future extension of World Drive, presenting the opportunity to orient the pole where it would have greatest visibility near highway I-4 and the new Disney entrance.
With the exact geometry determined for the trademarked mouse head, requests for bids were sent to traditional steel-pole suppliers for the 105-ft (32 m) pole. North American Pole Corp. (NAPCO), Dallas, Texas, U.S., was awarded the contract.
Although the geometry of the pole was settled, many details had to be worked out involving shipping, constructability and finish on the pole. While it would have been convenient to bring the entire assembly of head and ears to the site for placement on the top of the pole, the 30-ft (9.1-m) diameter head and the 18-by-20-ft (5.5-by-6.1-m) ears could not be shipped in one piece. Cutting down the head to a size that could be shipped presented a problem of field welding and painting. The best solution was to make the head and ears in sections with flange plates at logical places on the head where an insulator or static wire was to be attached. This solution permitted galvanizing the entire structure, shipping it safely and building it with normal construction techniques.
The head and ears were made from 12-by-20-inch (305-by-508-mm) rolled shape structural tubing in compliance with the American Institute of Steel Construction's specifications. These shapes were rolled in Chicago, Illinois, U.S., and bent by Bend-Tec of Duluth, Minnesota, U.S., which had just fabricated the Olympic rings for a bridge in Atlanta for the summer games.
The induction bender rolled out the shape in a constant radius bend, which made the 30-ft (9.1-m) diameter head. The ears presented a different problem since they were shaped in 18-by-20-ft (5.5-by-6.1-m) ellipses. The ellipses were made out of two different constant radii circles, requiring precise work during bending and fabricating.
Shipping Once bent, the sections for the head and ears were shipped to Dallas to be fabricated by NAPCO, which drew the outline of the ear on the floor of the shop and cut and welded the bent sections to fit. The second ear was made on top of the first to ensure that they would be exact copies of each other. The head was assembled in a similar manner.
The material for the neck, weighing 14,000 lbs (6350 kg), was cut with a plasma cutter which read an Auto-Cad design file and cut the shape exactly. The entire head, assembled on the ground to make sure that the pieces fit properly, was then disassembled and shipped to Houston, Texas, to be galvanized. Galvanizing was completed in one week, and the structure was shipped to the substation site.
Lighting Disney's artists produced a rendering of the structure at night, depicting rings of lighting outlining Mickey's head and ears. As the structural design process continued, different lighting options were investigated. Eventually, laser technology was selected. Rings of light consisting of fiber optic cable powered by a laser on the ground were placed around the head and ears (Fig. 7). Laser Fantasy, of Bellevue, Washington, U.S., demonstrated the laser system for Disney personnel and then finalized the design of the lighting system. The design involved a laser at the base of the pole, telecommunications-grade fiber running inside the pole to minimize any loss of light from the laser over a distance of 70 ft (21.3 m) to the neck of the pole, a distribution box mounted on the neck and lossy clear fiber cable outlining the head and ears.
Construction The original plan was to attach the ears to the head on the ground and lift the entire structure to the top of the shaft. Rather than lifting the 41,000-lb (18,597-kg) structure in one piece, Tampa Electric crews placed the 30,000-lb (13,608 kg) head onto the pole shaft, which had already been erected by Reliable Constructors, Orlando. Then, each ear was lifted and installed on the head (Fig. 6). The next week, our crews transferred the the conductors from the existing 230-kV circuit to the mousehead pole using polymer dead ends to minimize the visual impact of the insulators. Finally, Tampa Electric personnel worked with Laser Fantasy to install and test the laser system. On Feb. 15, 1996, the one-of-a-kind mousehead pole was complete.
The Osceola Substation and Osceola to Studio transmission line were placed in service on March 12, 1996, providing a new tie between Tampa Electric and RCID that ensures an ample and reliable power source to the Walt Disney complex. The Mouse-head Pole, as it is now known, serves not only as a trademark for Walt Disney World, but also as a symbol for the success of the project. TDW
Mike Leahy is a senior engineer in Tampa Electric's Transmission Engineering Department. He received the BSCE degree from Virginia Tech in 1988 and the MSCE from the University of South Florida in 1994. He is a registered professional engineer in Florida and a member of American Society of Civil Engineers.
Mike Kotch is a principal engineer in Tampa Electric's Transmission Engineering Department. He received the BSEE degree from the University of South Florida in 1985. He is a registered professional engineer in Florida, a member of the National Society of Professional Engineers, the Florida Engineering Society, and the IEEE Power Engineering Society.