| The retractable roof at Lucas Oil Stadium comprises two roof panels, each approximately 150 feet long by 600 feet wide, that weigh a total of 2.9 million pounds. The panels meet at the top of the roof to form the peak when in the closed position, and slide down along 5 parallel rails to rest over the lower half of the roof when in the open position. When the retractable roof is closed, a large movable cap covers the entire peak of the roof and provides a weather-tight seal between the two panels. Each of the two roof panels has two cable drums over the two outboard rails and has four cable drums over the three inboard rails, for a total of 16 cable drums per roof panel. Each cable drum is driven by four 7.5-horsepower motors for a total of 64 motors per roof panel. The motors are controlled by sophisticated variable frequency drives (VFDs) that work together and ensure that all cable drums maintain the correct cable tension to share the roof loads equally. As the retractable roof panels roll downhill to the open position, the electric motors must restrain rather than drive the load, and in the process act as generators in order to keep it from running away. Each VFD is equipped with an integrated regenerative drive that turns the generated power back into regular 60Hz current and feed it back into the power grid. This system keeps the roof panels under control as they roll downhill to the open position, and provides a little extra energy, which can be used to drive the ... |
