Transmission lines are the heavy cables strung between lattice towers or single shaft poles that carry power from where it is generated to areas where it is needed. The transmission network allows the movement of large amounts of electric power over long distances.
Electricity is generated by utilities and other energy producers at various types of power plants, wind and solar farms. (Pepco is an electric distribution company only and does not generate electricity.) Electricity is transformed or increased to higher voltages at substations before it moves into the network of high-voltage transmission lines. Electricity from the transmission line network is reduced to lower voltages at substations, and electric distribution companies then bring the power to homes and businesses.
Because electricity cannot be stored, it must be generated, transmitted and distributed at the moment it is needed. The high-voltage transmission grid is the vital link between power plants that generate electricity and the people who need it. To increase efficiency and reliability, regional transmission systems are connected to allow power to flow from one region to another.
The electricity we use each day in our homes is 120 volts. The high voltage of a transmission line is at 115,000 volts or more - that's about 1,000 times as strong.
The purpose of a substation is to change the voltage from long-distance high voltage transmission lines to the voltages used to supply our homes. The size of substations can vary depending on whether it serves mainly residential properties or commercial and industrial units.
Substations generally have switching, protection and control equipment, and transformers. In a large substation, circuit breakers are used to interrupt any short circuits or overload currents that may occur on the network. Distribution substations may use something called a recloser, a protection device for electrical distribution networks, circuit breakers or fuses for protection of distribution circuits.