By Chad Hall, COO, Ioxus (www.ioxus.com)
One hears a lot about power quality, but what is it and why is it so important? Most people are ignorant about the issues facing the utilities industry in its effort to provide high-quality, reliable power. However, if the power goes out, everyone pays attention. Several months ago, a local utility was required to shed load during a summer storm, and all of sudden it was big news. The issue was discussed for several days, and the point was clear; we take power and power quality for granted until it is not there.
With the advent of microcomputers and sophisticated control circuitry, power quality has become an important issue. The term “power quality” is rather vague and is defined differently depending on the context. A good operational definition of power quality is: power that does not impair the operation of a customer’s equipment. Good power quality today means a sinusoidal AC source that provides a stable voltage at a constant frequency within narrow limits. Power quality must be maintained, otherwise serious economic losses occur for customers. For example in the book, “Power Quality: VAR Compensation in Power Systems,” it is stated that in the production of glass, a five cycle interruption, which is less than one tenth of second, can cost $200,000 and a computing center experiencing a two second interruption of power results in a loss of $600,000.
Consumers expect utilities to provide uninterrupted power of high quality on a continuous basis and to adjust instantaneously to changing demand. Unlike most other products, electrical energy cannot be effectively stored, so that when an unexpected spike in demand occurs it often leads to a reduction in power quality and manifests in voltage sag, harmonic distortion and variations in frequency. In severe cases, excessive load can result in the necessity to take a generating facility offline, which might be caused by a low frequency trip. The lack of efficient storage methods requires utilities to keep a vigilant eye on demand and be prepared to bring reserve facilities into action at a moment’s notice in order to prevent power interruption.
The aging delivery infrastructure also affects power quality. The transmission lines in many areas are overloaded, leading to higher line and power losses due to reactance created by an ever-increasing inductive load. The power grid in the United States may be thought of as three regional grids that are loosely connected. The grid has evolved with no real long-range plan. As a consequence, the current grid system is a patchwork of transmission lines. The transmission lines that are used to interconnect the grid are aging and are being pushed to capacity. The line losses associated with the transmission of power increase exponentially with load, and as they are frequently required to perform at or near capacity, the loss of energy in the transmission process is significant. Unless the problems of the grid are addressed in the short term, the situation will worsen, resulting in more frequent widespread power outages, reduced power quality, and the possibility of equipment damage.
The ability to reduce reactive power from sloshing around in the grid would be a good first step. Reactive power is power produced by a utility that is not consumed, but rather is reflected by the load back to the utility; in short, reactive power is created by an impedance mismatch between the utility provider and the customer or load. Reactive power has always been a headache for utilities, but it is even more of a headache now that power quality is so important in the proper operation of modern electronic devices including computer networks and industrial controllers.
When power quality causes serious financial impact, the solution may, at least in part, have to be provided by the end user. One solution is the installation of a power conditioner. In the first instance, the power conditioner would have to provide an AC signal that did not vary in frequency. One straightforward way to do this is to store the power ahead of the conditioner as DC using a bank of capacitors and then using a DC-to-AC inverter to produce perfect 60 Hz AC. The expense of such a conditioner would be driven in large measure by the total power required. In the second instance, a ride-through solution would be appropriate. The good news is that with the advances in energy storage technologies, there are ways to store large amounts of energy. As the sophistication of power conditioners increases, their costs will come down, and it is very possible such systems will be available for a much wider spectrum of power consumers.
Based on the magnitude and importance of the problem, the solution to power quality is anything but simple. Ironically, the cry for green energy adds yet another layer of complexity to the problem and will, initially at least, drive up the cost of energy due to the lack of storage techniques. Both wind and solar power generation cannot be depended upon for a continuous flow of energy, making the utilization of such power more complex than from an ordinary power plant powered by conventional means. Utility operators are also hampered by environmental regulations on every front. The ability to construct new generating facilities or erect new transmission lines has become increasingly complicated due to the plethora of regulatory agencies. The unwillingness of the government and public at large to consider the nuclear option acts as another roadblock.
The bottom line is that if end-users require high-quality power, they will have to take a proactive role in the process. The expectation that the utility industry will solve power problems is naive. Using the power provided by the utility and conditioning it is one way to ensure high-quality power at a manufacturing or data processing center. Self-generation of power by ultracapacitors is another avenue large users can employ to reduce costs and obtain high-quality power. Regardless, high-quality power will be most readily available to those who take a proactive role in obtaining it