Electric distribution lines

There are a variety of types of distribution lines used to carry power from the distribution substation to end users. Distribution lines, also called feeders or mains, include primary feeders which are lines with voltages ranging from 4 to 35 kV, and secondary feeders with voltages below 4 kV.  

Lines include various types of equipment including conductors, poles (if overhead), switches and protective equipment, voltage regulators, and transformers.  

Here is the function of the equipment shown above:

  • Circuit breaker: Protective equipment that interrupts flow of power through an internal switch mechanism that is tripped by an unsafe surge of electricity.
  • Switch: Device that allows control over flow of power.
  • Recloser: A special breaker that is designed to open when a fault occurs on the part of the line to which it is connected. Through use of a timing device, the breaker will reclose a predetermined number of times so that if a short-term fault clears, service is automatically restored.
  • Fuse: Protective equipment consisting of a piece of metal that melts when overheated by excess electric flow.
  • Transformer: Device that adjusts line voltage.
  • Voltage regulator: Device used to adjust voltage along a line; includes booster transformers, capacitor banks, and static var compensators (SVCs).

Overhead electric distribution lines
Electric underground cable being installed in a trench

Distribution lines can be located overhead or underground. Overhead distribution is typically less expensive to run than underground. But overhead lines are susceptible to considerably more damage since they are exposed to natural events such as tornadoes and hurricanes as well as man-made events such as a car hitting the distribution pole. Overhead lines are, however, easier and less costly to access for service and repair since they are readily accessible, faults can be found through visual inspection, and lines don’t have to be dug up to make repairs.

Underground lines are at least twice as expensive as overhead lines and often even more expensive. They have much less exposure to damage, but repairs are more costly and time consuming, and it can be difficult to identify where a fault has occurred. Many communities prefer underground lines for aesthetic reasons. 

Other variations in types of lines include wye and delta configurations.

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