During the harshest cold weather this winter, some Midwestern utility companies asked residents to turn down their thermostats. But why?
The 2018-2019 winter season, so far, has provided record-breaking cold temperatures in the upper part of the country. During January’s polar vortex event, residents of the Midwest reported wind chills as low as -55 degrees Fahrenheit (-48 Celsius). This unprecedented cold took 21 lives before temperatures reascended to regular levels. Additionally, it forced the city of Chicago to set its train tracks on fire for railroad cars to pass along them without derailing.
However, during this time, some utility companies advised their customers to lower their thermostats and endure colder temperatures. The reason for this is actually quite simple: to avoid overtaxing the electrical grid that nearly every home in America uses every day. It may seem difficult to believe that the difference of a couple degrees per home could disrupt an entire regional power grid, since just five grids provide enough electricity to power the entirety of North America.
Many of us take the grid for granted. When we get a cold beverage from the refrigerator, we likely don’t consider the generating plant hundreds of miles away that helps keep the fridge cold. When we turn on a light switch, we don’t think about the conductors sending up to 765,000 volts to every area in their network. So what is “the grid” and how does it get overworked?
Understanding the Grid
When a generating plant produces power, the power gets sent to a nearby “switchyard” that houses transformers. Transformers are devices that can raise or lower electric voltage. At the switchyards, the transformers raise the voltage up to several hundred thousand watts of electricity. To prevent overheating, the coils are immersed in mineral oil, which in turn is cooled by fans or cooling fins.
Next, the energy travels along electrically conductive cabling called transmission feeders. These feeders are the main power supply lines leading from the generating plant on the way to our homes. Bare aluminum cable comprises transmission feeders and their counterparts, distribution feeders.
The next step involves the energy passing through a regional substation, which is a facility that manages electrical energy. At each substation, transformers do the opposite of the job they did at plant switchyards. They “step the voltage down to an intermediate level–typically between 35,000 and 138,000 volts–for sub-transmission to a series of smaller substations located closer to consumers,” said Dr. Stephen Ressler, Professor Emeritus from the United States Military Academy at West Point.
At the end of electricity’s journey, the smaller, local substations lower the voltage again to as little as 2,400 volts to prepare the energy for individual users. “Finally, just outside your home, the power is stepped down once more to 120 volts,” Dr. Ressler said.
Dealing with High Demand
When record-breaking winter weather approaches, keeping your house a cooler temperature isn’t a popular idea. Unfortunately, a surge in electricity use recently caused a fire at a natural gas compressor station in Michigan. This incident left many Midwesterners with a smaller supply of energy to heat their homes. In turn, the state’s government partnered with several utility companies and made such a request. They asked residents to lower their in-home temperatures to 65 degrees to help ease the burden on the remaining plants.
How does this happen? “The total electrical power generated within a regional grid must exactly meet the total demand for power at any given time,” Dr. Ressler said. He explains that when you use electricity, the increased demand for power slows down a generator miles away. The slowdown is minimal, but as Dr. Ressler said, “an automatic control system increases the flow of steam into the adjoining turbine.” This change adds torque to compensate for the slowdown and to keep the generator shaft turning at the necessary speed.
Sudden spikes in energy use lead to major problems. Generators overheat and cause fires like the one in Michigan. The regional grid reroutes power from most failing equipment, but the total output of energy is lessened. To prevent further incidents, residents must lower their energy consumption.
Electricians and engineers implement fail safes and backups to keep our world running, but no system is perfect. Lowering thermostats in the winter and raising them in the summer by just a few degrees can drastically impact your electricity bill and protect your community’s power supply.
Dr. Stephen Ressler contributed to this article.
Dr. Ressler is Professor Emeritus from the United States Military Academy at West Point and a Distinguished Member of the American Society of Civil Engineers (ASCE).