AC AND DC TRANSMISSION

Date: 2015-10-07; view: 540.

Read the text about the difference between AC and DC transmission and then complete the table.

AC (or alternating current) transmission refers to the transfer of energy from a source to one or more main receiving stations by electric current that reverses (alternates) its direction at regular intervals. DC (direct current) transmission involves the transfer of energy from a source usually to one receiving station by electric current that flows in one direction.

Key advantages of AC transmission technology are its flexibility and widespread use by electric utilities. AC facilitates future additions of intermediate stations, acting like exit and entrance ramps on an interstate highway, to serve local load centers and/or provide transmission access for new generation that may locate along the way. The ease of AC connections can encourage siting of fuel-diverse, newer technology and environmentally-friendly generators. Also, the use of AC technology enables expansion into a high-capacity transmission overlay that can be readily integrated with the existing systems. Integration can be achieved using commonly available step-down autotransformers or generator step-up transformers, offering the benefits of enhanced operating flexibility and reduced system losses.

By contrast, traditional DC technology is best suited for specialized applications, such as point-to-point transmission traversing unpopulated areas or where the systems being connected do not operate in synchronism. Examples include underground/undersea cables, long-distance overhead transmission serving as outlets for generating stations, and asynchronous links between two systems that have either no ties or very weak ties. While DC offers freedom from line charging currents and simpler line design with only one (monopolar) or two (bipolar) power conductors, it requires DC/AC conversion at each terminal to integrate with the existing system.