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ABB drives raising the roof in Phoenix

ABB Automation Technologies : 16 March, 2007  (Company News)
ABB variable speed drives are controlling the retractable roof at a new first-of-its-kind stadium in the United States.
The 25-acre stadium in Phoenix, Arizona and home to National Football League team Arizona Cardinals, is the first in the U.S to be equipped with both a retractable roof (that opens and closes to admit or shut out the sun or rain) and a retractable playing field built into a giant steel tray holding more than two acres of natural grass that will move in and out of the stadium on rails - the first of its kind in North America.

The $450-million stadium is widely considered an engineering marvel and has already been featured on the Discovery Channel series “Extreme Engineering” which highlights projects that extend the frontiers of engineering capability.

The dome-shaped roof of Cardinal stadium is unique, because its two retractable panels move in a sloping trajectory. ABB drives were chosen to combat the inherent risks associated with operating a sliding roof on a sloping track.

Designed by U.S. engineering company Uni-Systems, the dome-shaped roof is unlike any other previously constructed in that its two retractable roof panels move along a sloping trajectory. If the brakes holding the panels in place were released and the motors that power retraction failed to start, the panels would collapse and fall to the ground.

Each cable drum has a bull-gear along the outer rim, driven by four, geared 7.5 HP, 480 VAC brake motors, controlled by two 20 HP ABB ACS800 drives. RIGHT: Because the roof panels follow a sloped track, the builders wanted to be able to check drive torque before each roof motion to ensure the drive is fully operational. ABB is the only manufacturer that can measure characteristics from the motor at 0 Hz.

Pioneering design
“An important factor in choosing the ABB drives was to combat the inherent risks associated with running a roof on a sloped track,” says Lennart Nielsen, Uni-Systems’ senior electrical designer.

Nielsen explains that they wanted a variable frequency drive that would enable them to test the drive torque before opening the motor brakes to ensure that each drive was operational and capable of a 100-percent torque output.

The retractable playing field is set in a giant tray that moves in and out of the stadium on rails. It is more economical to move the field into the sunlight than to open the entire roof. ABB motor starters activate the motors that move the tray. Only three other stadiums in the world have retractable playing fields; two are in Europe, one is in Japan.

“We wanted to have this capability all the way down to a motor speed of 0 Hz, and none of the manufacturers, except ABB, could guarantee that,” says Nielsen.

The retractable roof consists of two movable panels divided into eight sections. Each section is powered by 16 motors and eight ABB ACS800 variable frequency drives that are maintenance-free and mounted in air-conditioned enclosures on the roof carriers.

The drives solution has been so successful that Uni-Systems has selected ABB to provide drives technology for two other retractable roof stadiums that the company is currently working on: the RCA Dome in Indianapolis and the Dallas Cowboys’ stadium in Texas.
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