Flywheel technology
May 1, 2007 12:00 PM, BY GARY RACKOW
As spring storms begin, stations should consider this technology as an alternative power system.
Continuous power is vital to the broadcast industry. People rely on television and radio in emergency situations, and being off the air as the result of a powerful weather or electrical event can result not only in lost viewers and listeners, but also in lost advertising revenue. In addition, a sudden loss of power can prove costly in terms of the damage that sensitive broadcast equipment can suffer due to an unexpected hard shutdown. As broadcast engineers continually seek better and more efficient solutions to address this situation, a new twist on an established technology is becoming a serious option when it comes to choosing the best uninterruptible power supply (UPS) solution.
The power gap
On October 17, 1989, the Oakland Athletics were squaring off against the San Francisco Giants in game three of the World Series. Oakland won the first two games, and the Giants were anxious to wrest some momentum back from their bay area rival.
As game time approached, the weather was beautiful. It was a typical Northern California afternoon, the diamond was meticulously groomed for the most important game of the baseball season, and game time excitement was building. As the players prepared for the game, the broadcast announcers ran through statistics and the various story angles that infuse baseball with its sense of drama.
Suddenly, people began to sense that something was wrong. The earth began to vibrate, and the fans assembling in the stadium became uneasy. Within moments, it was clear that nature was intervening in America's pastime and that this was a significant event. Al Michaels, the ABC Sports play-by-play commentator, addressed the audience with the following: “I'll tell you what; we're having an earth…” Michaels' commentary was cut short due to a power failure. ABC quickly had the power up and running and began broadcasting news coverage of the unfolding seismic events.
Michaels' words were lost in a “power gap,” the space between full power and backup power caused by the temporary interruption of power flow. The interruption can last for milliseconds, seconds or even a matter of minutes, but it can be disproportionably costly to broadcasters. With the sensitive electronic equipment now in use in almost every facet of broadcasting, even the slightest interruption of power, or the provision of poor quality power, can cause capital loss and mounting difficulties for engineers.
Historically, batteries have been the primary energy storage medium for UPS systems, but increasingly the broadcast industry is turning to UPS systems using flywheel technology. This change is occurring because flywheel technology has proven to be more reliable, more cost-effective and a more environmentally sound alternative to traditional lead-acid battery-based systems.
UPS systems meeting power grid challenges
According to a report created by the North American Electric Reliability Council, over the next 10 years, the demand for electricity is expected to increase 19 percent, while power generation will only grow by 6 percent. This alone points to the potential forces working against broadcasters who face considerable challenges and cost in maintaining continuous power for their operations. Power grid infrastructure shortcomings, coupled with erratic weather conditions, power surges and brownouts, are all serious sources of concern for broadcasters.
Fortunately, UPS systems are easily justified in studio broadcast applications that cannot tolerate any interruptions, including maintenance interruptions that are scheduled in advance. In these situations, the cost of the UPS system is usually a small part of the total infrastructure cost and the potential loss in revenue due to the interruption in program transmission.
Flywheel-based UPS systems are financially attractive to a wide range of broadcasting studios and transmitters sites. They can:
- reduce maintenance costs, particularly those related to batteries;
- reduce additional utility costs that result from UPS system efficiency losses;
- handle crowbar events and keep the transmitter protected; and
- improve UPS system reliability.
Maintenance and utility costs
Valve-regulated lead-acid (VRLA) batteries are commonly used at all UPS power levels. They are the predominant UPS battery used in studio operations because they cost less and require less space than conventional vented lead-acid batteries (wet cells).
Batteries, particularly VRLA batteries, are recognized as being the highest failure component of UPS systems. For a typical 240-cell battery system, one would expect a few batteries to fail in the first couple of years and then about 50 or more to fail in each of the next two years.
VRLA batteries predominantly fail in open circuits, so any single-cell failure results in failure of the entire battery system. Therefore, the mean time between failures of the entire battery system will be measured in months or weeks rather than years.
Additionally, batteries leak, are toxic and must be disposed of in a costly and environmentally sound way. Thus, eliminating batteries greatly improves overall reliability, and at the same time, eliminates the costs associated with battery maintenance and replacement.
Some flywheel UPS systems use a line-interactive design that makes them much more efficient than conventional double-conversion, battery-based UPS systems. As a result, utility costs resulting from UPS system efficiency losses are lower.
UPS systems designed with integrated flywheel energy storage can achieve efficiencies of 98 percent compared with 93 percent or 94 percent for conventional battery-based UPS system. In the 1000 kVA size range, such as at large transmitter sites, the difference can easily amount to an annual energy savings of $18,000 to $20,000. In addition to the electrical characteristics, the smaller space requirements and wider operating temperature range of flywheel UPS systems make them easier and less costly to retrofit and install.
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