Three-Phase Electrical Power

Joseph E. Fleckenstein

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351830034
• Edition: 1
• Topic: Ciencias físicas
• Subtopic: Energía

Three-Phase Electrical Power addresses all aspects of three-phase power circuits. The book treats the transmission of electrical power from the common sources where it is generated to locations where it is consumed. At typical facilities where electrical power is used, the book covers the important topics of grounding, currents, power, demand, metering, circuit protection, motors, motor protection, power factor correction, tariffs, electrical drawings, and relays. Included in the text are the necessary methods of computing currents and power in all possible types of circuit applications as those that are balanced, unbalanced, leading, lagging, three-wire, and four-wire.

Focusing on electrical gear, programs, and issues related to the generation and use of three-phase electrical power, this contemporary educational guide:

• Uses simple, straightforward language to explain key concepts and their underlying theory
• Introduces numerous examples, illustrations, and photographs to aid in comprehension
• Employs phasor concepts throughout the text to aid in the analysis of three-phase circuits
• Encourages applied learning by supplying practical problems at the end of each chapter
• Provides extensive references and a glossary of symbols, acronyms, and equations

Three-Phase Electrical Power delivers a much-needed modern-day treatment of three-phase electrical power for electrical engineering students and practitioners alike.

1

Alternating Current

The common forms of alternating electricity are single phase and polyphase. In the polyphase category, there are two types, namely, the two phase and the three phase. Two-phase electricity was popular in some areas years ago, but its popularity has dwindled, and today, the two common forms of alternating electricity are the single-phase and the three-phase types.

Alternating current (ac) originates at a generator that could be a single-phase or three-phase generator. A single-phase generator is generally of a smaller capacity and usually situated on site. Typical single-phase generators are in the range of 1–10 kW, although a few are larger.

Three-phase generators at an electrical utility may be as large as 1,300,000 kW (1,300 MW). The current generated at utility generators is commonly at a potential in the proximity of 35,000 V. The output from the three-phase generators is stepped up at transformers (SU transformers) to a high voltage that could be in the range of 140,000–500,000 V or higher. The high voltage facilitates transmission of current over long distances. Obviously, the higher the voltage, the lower the current for a given power level. And lower currents permit the use of smaller conductors. Close to the area where the electricity is to be used, the high voltage, in turn, is reduced to medium or low voltage for local distribution.

Users of large amounts of electrical power, as commercial facilities or industrial installations, are generally supplied with a three-phase electrical service. Within the installations, circuits would typically be divided into both single-phase and three-phase circuits. The three-phase circuits are used to power motors and possibly other large industrial-type loads. The single-phase branches of the three-phase service would typically be used for lighting, heating, fractional horsepower motors, and the like. A common North American electrical service to commercial and industrial users is the 480/3/60 ac service. (By convention, the “480” designates 480 V, the “3” designates three phase, and the “60” designates 60 Hz.) If the user has individual motors greater than, say, 500 HP, the voltage of the electrical service might ver...