ABSTRACT
The distribution system shown in Fig. 23.1 illustrates many of the features of a distribution system
making it unique. The voltage level of a distribution system can be anywhere from about 5 kV to as high
as 35 kV with the most common voltages in the 15 kV class. Areas served by a given voltage are
proportional to the voltage itself, indicating that, for the same load density, a 35 kV system can serve
considerably longer lines. Lines can be as short as a mile or two and as long as 20 or 30 miles. Typically,
however, lines are generally 10 miles or less. Short-circuit levels at the substation are dependent on
voltage level and substation size. The average short-circuit level at a distribution substation has been
shown, by survey, to be about 10,000 A. Feeder load current levels can be as high as 600 A but rarely
exceed about 400 A with many never exceeding a couple of hundred amperes.
