Basics of Electricity Transportation
Electricity is transported across distances through the power grid, a network of stations, substations, and transmission lines
Electrical energy is propagated either through direct current or alternating current
Transmission is more efficient at higher voltages
Electricity must be used as soon as it is generated, so power grid systems are built to balance demand and generation
Once electricity is generated by the conversion of a different primary energy source, humans transport this electrical energy across distances via the power grid. Once it reaches consumers, it is converted into another form of energy, such as mechanical motion, light, or heat. Because electricity is a flow of electrons, it cannot be stored and must be used immediately once it is generated.
How we transport electricity
A complex network of stations, substations, and transmission lines (the “power grid”) transports electrical energy from where it is generated to where it is consumed. The United States currently has three separate systems of power grids, or “interconnections”: the Eastern Interconnection, the Western Interconnection and the Electric Reliability Council of Texas (ERCOT).
Efficiency in electricity transmission: Direct current, or DC, electricity is the simple flow of electrons in one direction through a wire. Direct current is very effective in transmitting electricity over short distances for immediate use, but it is inefficient to transmit over long distances.
With alternating current, or AC, electrons alternate their direction of movement through a wire, going back and forth instead of only moving in one direction.
Due to certain physical principles beyond the scope of this module, alternating current is easier to generate and can be stepped up to higher voltages (essentially electric pressure) for more efficient transmission across long distances. Alternating current can be used directly in applications where the electrical energy is dissipated as heat or where the direction of the current doesn’t matter (like in appliances like an oven or an incandescent lightbulb), but must be converted back into direct current for other applications such as computers, LEDs, and other devices that run using batteries.
Because electrical energy dissipates over distances, it is much more efficient to transmit at high voltages. This is because higher voltage means the wires can transport electricity at a lower current through the wire, and therefore they will exhibit less energy loss.
Near the generator source, the voltage of the generated AC is increased up to tens or hundreds of thousands of volts using a transformer before the electrical energy is transported over long distances along transmission lines.
The voltage is then decreased at a substation to the standard line voltage that you might see in a city or neighborhood (usually 7,200 volts). Outside of the building where the power will be used, the voltage is reduced again to 240 volts with a transformer that you might see on an electrical pole. These numbers can be slightly different in different countries.
Electricity must be used as soon as it is generated. Power grid systems are built to balance demand and generation. If demand is very high and supply can’t keep up, the power grid can fail, leading to a brownout (drop in voltage) or blackout (shutdown). This imbalance can result from a breakdown at a power generating station or damage to part of the grid due to bad weather or some other failure. To stabilize the grid, grid operators often seek to diversify supply including through storage; manage excess demand; and protect equipment against weather-related failures.
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Questions for deeper thinking
What are factors that need to be considered for incorporating renewable energy sources into existing power grids?
What are possible threats to the grid?
Why are high voltage transmission lines needed?
What are the pros and cons of having three different grid systems in the United States? When might this be beneficial and what are some of the challenges that might accompany this distribution?
Sources and further reading
Energy Information Administration: Energy Explained - Electricity, Delivery to Consumers
Wikipedia: Electromagnetic Theory
How Stuff Works: Power Grids
Page last updated: August 31, 2022