Electric power originates in power plants. It is transmitted by transmission lines from the power plants to the loads. Along the way, the voltage is ﬁrst stepped up by transformers, generally within the power plants, from a level that is practical for the generators to a level that provides adequate efﬁciency for long-distance transmission. Then, near the loads, the electric power is stepped down, also by transformers, to a voltage useable by the customer.
Let’s take a detailed look at the journey of electrical energy. From the power plant to the house…
Electrical energy is generated in large generators at a power plant. A generator is a device that converts mechanical energy into electrical energy. The process in the generator is based on the relationship between magnetism and electricity. Typically an electric conductor, such as copper, spins within a magnetic field to produce electrical energy.
An electric utility power station uses a turbine, engine, water wheel, or another similar machine to drive an electric generator. An electric generator converts mechanical or chemical energy to electrical energy.
The energy used to spin the turbine can come from natural gas, coal, falling water, nuclear energy, and renewable resources such as wind, geothermal and solar energy. At power stations, electricity is typically produced at less than 30,000 volts.
Before entering the transmission lines, the electricity is stepped up to high voltages by electrical transformers. Because electricity must travel long distances from the power plant to consumers. The transformer allowed electricity to be efficiently transmitted over long distances. This made it possible to supply electricity to the users located far from the power plant.
After stepping up voltage, transmission lines are used to carry the electricity to a substation.
The transmission lines carry electrical energy over long distances from the power plant to the areas of demand. The electricity in transmission lines is transported at voltages of over 200 kV to maximize efficiency. Voltages of 220 kV to 500 kV are typical. Transmission lines are usually attached to large lattice steel towers or tubular steel poles.
A transmission substation connects two or more transmission lines. There are high-voltage switches in the transmission substation that allow lines to be connected or isolated for maintenance purposes. A large transmission substation can cover many acres with multiple voltage levels, and a large amount of protection and control equipment such as capacitors, relays, switches, breakers, voltage, and current transformers.
Subtransmission lines carry electrical energy at voltages less than 200 kV. (Typically 66 kV or 115 kV) Subtransmission lines are usually suspended on tall wood or steel poles. They can also be placed underground.
Electrical energy is often distributed via alternating current (AC), although the direct current is sometimes used for long-distance, high-voltage transmission.
Distribution substations are generally located closer to consumers. A distribution substation has step-down transformers that reduce the voltage from high voltage to lower voltage. Because it is not economical to directly connect consumers to the high voltage transmission network unless they use large amounts of energy.
Electrical energy is transferred to distribution lines from the distribution substation. These lines cover much shorter distances and are typically energized at 16 kV, 12 kV, or 4 kV. Lower-voltage distribution lines carry electricity to neighborhoods on shorter poles or underground. Transformers located on distribution poles, on a concrete pad on the ground, or underground further step down the voltage before it is delivered to the end-users.