When American Electric Power (AEP) designed its new Energy Delivery Headquarters, one of the things they knew they would need was a premium grade of power.
For a business operation with a PC on every desk, the risk of losing power even momentarily to the PCs and servers was unacceptable. After considering several alternatives for premium power quality in the new office building, AEP's team selected an uninterruptible power supply (UPS) system with an Active Power flywheel.
"We looked at a number of ways to protect our sensitive digital equipment," according to Bruce Renz, Vice President of Energy Delivery Support for AEP. "The Active Power solution was the best technical and economic solution for our specific situation."
The UPS-and-flywheel solution enables the group to run their PCs with little fear of interruption.
American Electric Power's Flywheel-based System
The solution selected combines a UPS with flywheel technology, an energy-storage technology which the Electric Power Research Institute (EPRI) describes as "an economical and elegant alternative to other methods of storing and providing premium power."
Although flywheels have been around since the days of the spinning wheel, there is nothing old-fashioned about the flywheel component of the system. It is a totally integrated motor-generator-flywheel, 11 inches high and 31 inches in diameter, that can produce 200 kVA of power.
The system combines an MGE UPS rated at 150 kVA with an Active Power CleanSource CS 200 flywheel rated at 200 kVA. The office building's power distribution environment consists of one group of electrical panels for standard power and a separate group of panels -- served by the flywheel-based system Ñ for premium power. Each PC user in the building has a designated orange electrical receptacle in their work space for premium power delivery.
The UPS converts AC power to DC power and the flywheel, which is connected to the DC side of the converter, provides energy to the DC bus. Then, on the device output, the DC power is converted back to AC power to serve the premium power circuits. This way, if there is any voltage sag or interruption on the source side of the device, the DC bus Ñ supported by the flywheel Ñ can convert to a generator state and provide the energy for AC power to continue to come from the unit.
The CleanSource family of flywheels delivers a power density of 50 kW per square foot and is offered in a range of models from Active Power. Each CleanSource flywheel is a simple, two-terminal DC device for providing safe, reliable energy in situations where a higher-than-standard quality of power is desirable. (The range of products corresponds to the popular power ranges of typical UPS systems.)
A Centralized, Cost-efficient Solution
AEP's UPS-and-flywheel solution employs one UPS for the entire installation, rather than using a separate UPS for each PC Ñ or even each floor of the four-story building.
"Having separate UPSs would have required more space and more maintenance," explained Vollkommer. "We're more comfortable with a centralized approach. It's less costly to centralize. With individual UPSs, you'd have a higher kVA, because you'd be adding more capacity at each individual PC site." According to Joe Pinkerton, the president of Active Power, the centralized type of solution costs about half as much as purchasing individual UPS devices for each desktop PC. The centralized approach also greatly simplifies the hassle of reconfiguring offices and computer systems.
In addition, centralization helps control costs because it requires less capacity to serve a diversified load. This is because not everyone is using their PC at the same time. "The diversity of the PC load can be handled with less capacity when using a centralized device vs. distributed UPSs," concluded Vollkommer.
Capabilities and Costs
One characteristic of battery-based UPS systems that has made them popular choices for providing reliable premium power is their ability to meet power requirements for several minutes. A 200 kVA flywheel, on the other hand, may be good for only a minute or less of power. But since most power quality problems occur in less than a minute, the flywheel meets most users' needs very well. The flywheel alternative from Active Power offers a longer life (20 years), low maintenance and a relatively small footprint, and it raises no environmental concerns.
According to IEEE, when you look at building power served by distributed circuits, 80 to 90 percent of the disturbances are momentary. In AEP's case, with a 200 kVA flywheel connected to a 150 kVA UPS system, they have about 20 seconds of back-up power available at full rating. And because they generally operate at about 60 percent of full rating, they really have 30 to 40 seconds with the flywheel -- more than enough to handle any voltage sag or momentary interruption they are likely to see. In fact, the flywheel has performed flawlessly on every occasion when it has been called upon since June, 1998.
With regard to cost, the team found the initial cost for a flywheel was very attractive.
Finally, according to Vollkommer, "our company is known for trying new things to gain the competitive edge for the future." While the flywheel may be based on one of the oldest technologies known to humankind, it's definitely on the leading edge of alternatives for power storage and delivery today. Today's flywheels still function basically as vessels for storing mechanical energy in the form of kinetic energy. Unlike earlier versions, however, they can now be manufactured from advanced materials that make them lighter and stronger. As a result, they can spin at a faster rate, which means that they can store energy extremely efficiently.
The Growing Need for Premium Power<P> Today, the continually increasing demand for and dependence on computers and connectivity in business is fueling a growing need for higher power quality. As an article in the May 31, 1999, issue of Forbes put it, "With refrigerators, light bulbs, and ovens, a blip in the current is merely an inconvenience. With computers and routers, it can be a catastrophe." The standard level of power delivered in the US today may be perfectly fine for most non-computerized applications, but PCs and related products in critical environments often need higher power quality to ensure their reliable operation.
The search for ways to deliver clean power to critical systems has generated a number of alternatives for storing energy and providing premium power, including superconducting magnets, batteries and flywheels. More than 40 flywheel systems from Active Power are installed across the US, demonstrating the viability of this technology.
Now, when AEP's commercial customers ask about ways to improve power quality in their businesses, it's not unusual for the company to use its own installation as an example.
A Proven Success in a Year of Operation
Never having been tried by the company before, the UPS-and-flywheel solution was met with initial skepticism among many PC users at AEP. But it didn't take long to prove itself. During its first year on the job, it has performed flawlessly, maintaining power to the PCs every time (with the longest interruption to the building lasting 35 seconds, when the building was transferred to an alternate circuit).
"It has made some believers over time," said Vollkommer. "Now what I hear is, "Hey, Harry, the lights went out yesterday, but my PC stayed on. Good job!'" ET