Electric power transmission
Electric power transmission
Electrical energy from power plants is transferred to substations located near cities. This is called electric power transmission.
Transmission lines are high-voltage transmission networks. They аrе usually called "power grids" or simply "the grid".
Electric power is usually transmitted through overhead power lines. Underground power transmission lines through cables are more expensive but are often used in cities.
Overhead transmission lines
Overhead AC transmission lines usually carry 3-phase current.
The voltages can be different according to the particular grid system they belong to.
High-voltage overhead lines are made of aluminium wires not covered by insulation. Wires have several strands and are often reinforced with steel strands. Copper was sometimes used before for overhead transmission but aluminium weighs less and is cheaper.
Overhead conductors can have cross sectional area from 12mm2 to750mm2. Transmission voltages are usually 110kV and above. Voltages 66kV and 33kV are sometimes used on long lines with small loads. Voltages less than 33kV are usually used for distribution.
Insulators are usually made of porcelain or glass and can be stacked in a suspension insulator string. They hang from a cross arm on a tower or pole and support the line conductor
A pothead is a type of insulator with a bell or pot-like shape used to connect underground electrical cables to overhead lines. Potheads are mounted on a distribution pole.
Bus support insulators are porcelain or fiberglass insulators that serve to isolate the bus bar switches and other support structures and to prevent leakage current from flowing through the structure or to the ground. These insulators are similar in function to other insulators used in substations and transmission poles and towers.
Oil circuit breakers are used to switch circuits and equipment in and out of а system in a substation. They are oil filled to provide cooling and to prevent arcing when the switch is activated
Capacitors are used to control the level of the voltage supplied to the customer by reducing or eliminating the voltage drop in the system caused by inductive reactive loads
Circuit switchers provide equipment protection for transformers, lines, cables, and capacitor banks. They also are used to energize and deenergize capacitor banks and other circuits.