Power system distribution involves delivering electrical energy from power plants to consumers through a network of transmission and distribution systems. The process begins at power plants, where energy from coal, gas, nuclear, water, and wind is converted into electrical energy. These plants use three-phase generators, typically rated between 50 to 1300 MVA, with terminal voltages ranging from a few kV to 20 kV, depending on the size and age of the units.
The transmission system is designed to reduce energy losses by using high voltages. Generator step-up transformers at power plant substations increase the voltage and decrease the current for efficient long-distance transmission. The transmission system has three main functions: delivering energy from generators to the system, providing for energy interchange among utilities, and supplying energy to subtransmission and distribution systems.
The subtransmission system consists of step-down transformers and lines that connect bulk power substations to distribution substations. These transformers step down high transmission voltages to levels suitable for distribution, often supplying large industrial loads or specific regions.
The distribution system includes distribution substations, which decrease the subtransmission voltages to primary distribution levels. These substations also protect the system with circuit breakers and surge arresters. Feeders distribute electricity to several three-phase sections connected through various protective devices.
The distribution network has two main parts: primary and secondary distribution. Primary distribution transfers electricity from substations to distribution transformers, stepping down the voltage to secondary levels. Secondary distribution connects to customer premises via service conductors, providing power for residential, commercial, and light industrial use. Service conductors connect through meters for billing and planning and to service panels on customer premises, which contain circuit breakers or fuses that supply power to various devices.
