Voltage flicker can be rather a nuisance to consumers of electric power. These fluctuations in electric voltage can arise when residential customers are situated close to such facilities as lumber mills and facilities with pumps or arc furnaces, in which a heavy electrical load is varying rapidly, or in which electrical motors undergo multiple starts and stops. Under certain circumstances, the neighbors of these facilities may experience uncomfortable flickering lights and jitters in their television pictures. Computers may freeze up, and heat pump controllers may go on the fritz.
Using solid state technology, UW researchers have developed a compensator called the Adaptive Var Compensator, or AVC, which dramatically reduces these kinds of disruptions in electrical power service. The AVC is a rapidly-switched shunt capacitor that eliminates fast voltage fluctuations without affecting longer-term variations of the system.
UW electrical engineering professors Mohamed El-Sharkawi and S. (Mani) S. Venkata developed and field-tested five different types of AVCs for industrial or commercial power applications from 1983 to 1993, with support from the Bonneville Power Administration and Southern California Edison. The researchers have tested AVCs at several sites around the Northwest and California, including the UW Medical Center, a lumber mill, a rock-crushing plant, and two wind-generation farms. The UW research has resulted in three U.S. patents, and the technology has been commercialized to benefit both consumers and power utilities. El-Sharkawi notes that Trench Electric, a major international power company, has commercialized the technology, with some 30 to 40 systems installed or on order.
The technology offers a way to solve flicker problems in a simpler and more inexpensive way than previously possible. For example, at one test site in Oregon in the area of the Coos Curry Electric Cooperative, a lumber mill at the end of a long rural "feeder" (electric power distribution line) was causing a flicker problem for about 250 residential customers nearby. "One solution to the problem would be the installation of a substation closer to the mill site," observe El-Sharkawi and Venkata. "However, the revenue generated by the customers on the feeder couldn't justify such an expensive substation." AVC technology implemented there by the researchers was successful in reducing flicker magnitude below perceptible levels.
AVCs were installed at the Devers and Tehachapi wind-generation farms in the Southern California Edison service area in 1982 and 1986, respectively. Systems to produce electric power from the force of the wind are of interest as an alternative energy source. But the unevenness of the power they produce causes problems for the local grid, increasing the cost and diminishing the advantages of wind-generated electricity. Utilities have been searching for solutions to the problem. The UW devices were studied as a low-cost, simple solution. AVC units at the two California wind farms have logged more than 10,000 hours of successful operation, demonstrating the viability of the approach.
During the period from 1987 to 1991, an AVC device was installed at the UW Medical Center where induction motors at a four-elevator tower were creating voltage flicker problems for some of the critical loads at the hospital. On top of that, the problem was resulting in power-factor penalty charges to the UW. The penalties result from something called reactive power loss that occurs in any kind of system that has wire coils, as motors do. In such systems, a certain quantity of power is consumed that cannot be transformed into useful work. Reactive power limits the amount of useful electricity that can be delivered, and power companies charge penalties for it. The AVC device eliminates this reactive power from utility lines.
In the case of the UW Medical Center, an AVC unit alleviated the voltage flicker problem, saved money by avoiding the penalty charges, and freed up enough equipment to eliminate the need to redesign a substation panel and related systems. Moreover, the loads can now be supported with only one transformer at the substation rather than the initial requirement of two transformers. The researchers estimate that, since its installation, this AVC has saved the University about $1,500 per month, or a total of over $22,500 in power-factor penalty charges. The UW is considering ways to improve its entire power system in this fashion, which would allow the institution to avoid a power-factor penalty of about $10,000 per month.