By Arjun Bhatia

At the dawn of electrical power nearly 150 years ago, power was generated where it was needed using coal-fired plants, providing power to big cities and industrial centres. As the need for electricity expanded outside the major cities and demand increased, coal proved to be too expensive for commercial use. The cheaper alternative was to produce power using a few hydroelectric power stations and transfer it across vast distances to locations it was needed. This led to a new system of transmitting electricity: the power grid [1].

Why is it called a grid?

When we think of a grid we might think of neat, ordered rows and columns, perhaps in this case of long power lines stretching across vast swathes of land, like a sheet of graph paper. In reality, the grid looks more like a web, or branches of a tree, with larger branches splitting off into many smaller ones, and those smaller ones splitting off even further, until eventually the smallest branch is reached, one that goes to your home, school, or another of the countless buildings supplied by this network [2].

What are the different parts of the grid?

Modern power grids consist of four major stages: generation, transmission, distribution, and the loads.

The first stage, generation, is any method by which electrical energy is produced, using different systems such as solar, wind, hydroelectric, nuclear, and more. Be sure to check out this article to learn more about all these different types. Once the electricity is generated, it needs somewhere to go, which is where the second stage, transmission, begins.

Before the electricity is transmitted over power lines, it needs to be stepped up to a higher voltage, usually 100,000 to 300,000 volts, and in turn, a lower current (be sure to check the bonus section on the end for more on that) [3][4]. The cables are typically composed of many-stranded aluminum wires for conducting electricity, with a steel core for strength [5]. After it has been transmitted close enough to its destination, the next stage begins [3].

Stage three is distribution, specifically to the buildings where electricity is being used. You might have noticed those green boxes on the streets around your home, accompanied by a quiet hum. First, do not touch them! Secondly, these are the final agents in the distribution phase. The hum is the stepping-down of voltage to the 120 V we get at our homes [3].

Our homes (and other buildings) are the fourth and final stage of the grid: the loads. A load is anything that converts the power into useful work. From the green boxes, the power goes to our homes’ own miniature grids to power our heating, lights, smart devices, stoves, and anything else you plug into the wall [4].

How does the grid look today?

Technology is constantly changing and evolving, and power grids are no exception. With the advent of more powerful and reliable computers, this century has seen the growth of ‘smart grids’, which relies on computers and software to automate and adjust various parts of the grid as needed. Using sensors, different parts of the grid can communicate with the stations generating and transmitting power to adjust the amount of electricity produced as demand fluctuates throughout the day [6].

In more sophisticated systems, during a blackout, the grid is able to recognize which areas are in the dark and reroute power from different areas. As other technology such as rechargeable batteries improve, the grid is able to allocate extra power to storage and withdraw this surplus if it detects a spike in demand [7].

Bonus: What was that thing about high voltage and low current?

As mentioned earlier, before transmitting power, the generated electricity is stepped-up to extremely high voltages. So… why? For this, we need to break down some of the physics.

To use an analogy, if electrical power in a power line is water flowing through a pipe, the current is the flow rate of the water and the voltage is the pressure that is pushing the water along. Both current and voltage are directly responsible for the amount of power being transmitted, so as long as one remains high while the other is low, the same amount of power can still be transmitted. Assuming you can not change the speed of the water, the only way to increase flow rate is to build wider pipes, which is not only expensive, but also makes them heavy, and for power lines that need to be supported by towers, this is not a viable option [8].

What would be better is, instead of relying on high flow rate for all that power, focus on high pressure, in this case, voltage. This keeps the power lines thin and light, while still maintaining the necessary amount of power [8]. As the electricity gets closer to its destination, it is more viable to build thicker cables, and the voltage can gradually be stepped down to the relatively safe 120 V used in homes. The green box mentioned earlier is actually the last of many substations where the power is stepped down to lower and lower voltages [3].

References

[1] “WaterHistory.org.” http://www.waterhistory.org/histories/waterwheels/ (accessed Nov. 25, 2020).

[2] “Ontario energy quarterly: electricity in Q1 2020 | Ontario.ca.” https://www.ontario.ca/page/ontario-energy-quarterly-electricity-q1-2020 (accessed Jan. 25, 2021).

[3] “Electrical grid - Energy Education.” https://energyeducation.ca/encyclopedia/Electrical_grid (accessed Jan. 27, 2021).

[4] “How the Electricity Grid Works | Union of Concerned Scientists.” https://www.ucsusa.org/resources/how-electricity-grid-works (accessed Jan. 27, 2021).

[5] “Power Transmission | Cables | Hydro-Québec.” http://www.hydroquebec.com/learning/transport/lignes-pylones.html (accessed Jan. 28, 2021).

[6] “Smart Grid: The Smart Grid | SmartGrid.gov.” https://www.smartgrid.gov/the_smart_grid/smart_grid.html (accessed Jan. 27, 2021).

[7] “Grid Modernization and the Smart Grid | Department of Energy.” https://www.energy.gov/oe/activities/technology-development/grid-modernization-and-smart-grid (accessed Jan. 28, 2021).

[8] “Transmitting Electricity at High Voltages.” http://www.betaengineering.com/high-voltage-industry-blog/transmitting-electricity-at-high-voltages (accessed Jan. 27, 2021).

Tech Breakdown: How the Grid Works