The electric delivery system is the set of facilities that produces electricity and delivers it to consumers.
Electricity is generated by power plants, also called generation facilities. Traditionally these have most commonly been connected to the transmission system and called centralized generation. But in recent years generation connected to the distribution system, called distributed generation, has grown.
The voltage created by centralized generators is generally several thousand volts. This voltage is then raised to the voltage of the transmission grid using step-up transformers located in a substation adjacent to the power plant. The electricity then enters the high-voltage transmission system where it is transported long distances.
As the electricity approaches an area where it will be consumed, the voltage is dropped to a safer lower voltage. This is performed by transformers located in distribution substations. The electricity is then delivered via lower-voltage distribution lines until it reaches a customer location. At or near the customer service line, the voltage is often again reduced to the voltage desired by the customer. This reduction is performed by a service transformer. Finally, the electricity is metered and flows into the customer’s internal wiring.