18.1 ELEMENTS OF DISTRIBUTION PRACTICE

Distribution Defined. Broadly speaking, distribution includes all parts of an electric utility system between bulk power sources and the consumers' service-entrance equipments. Some electric utility distribution engineers, however, use a more limited definition of distribution as that portion of the utility system between the distribution substations and the consumers' service-entrance equipment. In general, a typical distribution system consists of (1) subtransmission circuits with voltage ratings usually between 12.47 and 245 kV which deliver energy to the distribution substations, (2) distribution substations which convert the energy to a lower primary system voltage for local distribution and usually include facilities for voltage regulation of the primary voltage, (3) primary circuits or feeders, usually operating in the range of 4.16 to 34.5 kV and supplying the load in a well-defined geographic area, (4) distribution transformers in ratings from 10 to 2500 kVA which may be installed on poles or grade-level pads or in underground vaults near the consumers and transform the primary voltages to utilization voltages, (5) secondary circuits at utilization voltage which carry the energy from the distribution transformer along the street or rear-lot lines, and (6) service drops which deliver the energy from the secondary to the user's service-entrance equipment. Figures 18-1 and...