ABSTRACT
In a broad denition, the distribution system is that part of the electric utility system between the bulk power source and the customers’ service switches. This denition of the distribution system includes the following components:
1.Subtransmission system 2. Distribution substations 3.Distribution or primary feeders 4.Distribution transformers 5.Secondary circuits 6.Service drops
However, some distribution system engineers prefer to dene the distribution system as that part of the electric utility system between the distribution substations and the consumers’ service entrance. Figure 4.1 shows a one-line diagram of a typical distribution system. The subtransmission circuits deliver energy from bulk power sources to the distribution substations. The subtransmission voltage is somewhere between 12.47 and 245 kV. The distribution substation, which is made of power transformers together with the necessary voltage-regulating apparatus, buses, and switchgear, reduces the subtransmission voltage to a lower primary system voltage for local distribution. The three-phase primary feeder, which is usually operating in the range of 4.16-34.5 kV, distributes energy from the low-voltage bus of the substation to its load center where it branches into threephase subfeeders and single laterals.
