It s Friday. Your boss gave you a deadline to have that report done by close of business. You re almost done with the report. So you don t bother to save it. Then your computer freezes. You re upset. You take a deep breath, say a prayer, and reboot your computer. You ve lost several hours of work. You may have lost a promotion and certainly a chance to impress your boss. You decide to work overtime and vow to back up your material more often. You re not alone. What may have been an annoyance to you and your boss multiplied many times has become a costly problem throughout the United States and the world. In many cases where offices and factories have become dependent on the smooth operation of computers, a single outage can be very costly. For example, a glass plant in 1993 estimated that an interruption of power of less than a tenth of a second can cost as much as $200,000, while for a computer center that experienced a 2-second interruption, it can cost $600,000 and a loss of 2 hours of data processing. According to Science ( Editorial: Magnetic Energy Storage, October 7, 1994), costs due to power fluctuations in the United States range from $12 to $26 billion. Consequently, the United States market for power quality services and equipment has grown to over $5 billion in 1999. Figure 1.1 shows how the cost of power quality disturbances have increased over the last 30 years.

Figure 1.1: Increase...