The sudden availability of electrical power at the end of the nineteenth century was followed by an array of inventions that took advantage of this wondrous discovery.
Today, electricity is used to illuminate buildings, to operate air conditioners, and to power trains. Electricity powers computers, copiers, medical devices, radios, televisions, and an ever-increasing variety of devices that continue to greatly improve the quality of life for millions of people the world over. At the core of it all is three-phase electrical power.
In the early years of electricity, there were two new promising and competing forms of energy. For a number of years, it was unclear as to which form, direct current (dc) or alternating current (ac), would prove to be more valuable or predominant.
Eventually, ac electricity became the preferred choice for most applications in part because it is a form of power that can be run through a transformer, converted to a high voltage, and transmitted efficiently over long distances.
There is still a place for dc electricity, for example, as power for commuter trains, but by far ac has become the more commonly applied form of electricity.
It is fair to say there are two general types of ac: single phase and polyphase. In the United States, single-phase electricity is the commonly used form at the residential level.
As many devices, such as lights and computers, can use only single-phase electricity, there will long be a need for this type of electricity.
Some single-phase electricity originates in small single-phase generators, but most single-phase electricity is derived from a three-phase supply. The category of polyphase alternating electricity includes two-phase electricity and three-phase electricity.
Two-phase electricity had its advocates early in the acceptance of ac. Today, there remains a limited use of two-phase electricity, primarily in the Great Lakes and the upper New York areas of the United States.
The development of three-phase electricity in the early days was hindered in part because engineers at the time had difficulty with the related mathematics.
A General Electric employee, Charles Steinmetz, who had extensive training in mathematics, is credited with the development of the mathematics that assisted in the adoption of three-phase electricity.
In particular, Steinmetz developed a method of using complex numbers and phasors to calculate three-phase currents and voltages. His first paper on the subject was presented in a conference in 1893 (Reference 1.1).
To this day, Steinmetz’s phasors remain a convenient tool for analyzing three-phase circuits, and phasors are used extensively in this textbook. In time, the merits of three-phase ac electricity became more apparent to those who were involved in the use and application of electricity.
Today, three-phase electrical circuits remain the most effective means of transmitting electrical current from the source where it is generated to the places where it is to be consumed.
And the three-phase motor is the most effective and practical means of converting electrical energy into mechanical power.
Public utilities that generate electricity have encountered a number of problems over the years in their quest to deliver economical, affordable, and reliable power to their customers. First, the expanding global demand for energy has resulted in the continually rising fuel costs of acceptable sources.
Deregulation in some states has resulted in affected utilities reexamining the way they plan, build, and finance new power plants. Increasingly restrictive environmental laws have brought about a new set of problems and challenges to public utilities.
In response to an ever-changing world, utilities are continually devising programs basically to provide a fair return on their investments. The objectives of these programs are mostly to more fully utilize existing plants while postponing the construction of new plants.
The rising cost of electricity has also encouraged users to examine the ways they use electricity, and many are embarking on programs and methods to reduce the monthly bills. Internal energy audits have consequently become more popular.
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