Updated: May 4, 2021
Rotating outages (a.k.a. rolling blackouts) were once the last resort during a power crisis. But in recent years, they are becoming more common in response to winter weather, heat waves, windstorms, and extreme wildfire conditions.
Residents of California have experienced them yearly as a form of wildfire prevention, and Texans are currently trying to stay warm while their electricity rolls in and out. With few standards in place to oversee rotating outages, electric utility companies can implement outages that last from 30 minutes to several hours, causing economic disruption and hazardous conditions for customers.
In this post, we will focus specifically on rotating outages being used in response to the excess demand on the grid that often occurs during heat waves or extreme cold. We’ll take a look at the problems they can cause as well as the necessary improvements that need to be made to minimize hazards to businesses, residences, and critical infrastructure such as hospitals.
Let’s take a look at exactly how rotating outages work.
Rotating Outages Explained
During heatwaves or cold snaps, residential and commercial customers demand more energy for cooling or heating in response to the weather. Rotating outages are implemented because the demand for power exceeds the supply of available power, or in engineering terms, load exceeds output.
To operate efficiently, electric power grids must operate at 60 Hertz and 100% voltage. When the amount of load demanded exceeds the output of energy sources, frequency drops below 60 Hertz and voltage drops to less than 100%. If all energy sources are operating at maximum output and load still exceeds output, the only option for transmission system operators (TSOs) is to reduce the load.
To reduce customer load, TSOs will manually open one circuit breaker at a time, via remote control, at distribution substations on a rotating basis. To restore power, TSOs must manually close circuit breakers. They’ll then continue to open and close circuit breakers in a rotating fashion so that one set of customers is not without power for an excessive amount of time. But this is where the lack of standards starts causing major problems for customers.
There is currently no set standard for the amount of time that an individual circuit can be open. In some cases, a circuit may be open, and power shut off to a particular set of customers, for several hours before the outage rotates to a different set of customers. So when customers need power the most, they can be cut off for hours at a time.
Drawbacks to Rotating Outages
Rotating outages can cause serious economic disruption for businesses. When the power is out, productivity stops; restaurants can’t cook or serve food; grocery stores risk losing freezers full of perishable items; employees who depend on Wi-Fi can’t work. Since this can occur multiple times in one day, businesses face the potential for hours of lost time, as well as time spent recovering from outages. Individuals are also at risk of losing perishable items, which can include lifesaving medication that may have spoiled during the outage.
During rotating outages, people are forced to face temperature extremes without access to heat, as was the case when a winter storm hit Texas last week, or air conditioning, which occurred during a major heatwave in California last summer. This can lead to weather related illnesses, such as hypothermia or heat stroke. Vulnerable populations, such as young children or older adults, can be more susceptible to these illnesses, which can result in death in the worst cases.
Re-evaluating and Improving the Use of Rotating Outages
To reduce customer load in an economically efficient, hazard-reducing manner, electric utility companies must approach rotating outages with an effective plan in place before the outages are necessary. To establish this plan, each electric utility must first categorize their customer base and distribution lines. This will allow the utility to understand the impact of rotating outages on customers. Categories are outlined below.
For example, suppose an electric utility has 1000 distribution lines. Of these lines, 100 serve Type 1 customers; another 100 lines serve Type 2 customers. These 200 lines are exempt from rotating outages. The remaining 800 distribution lines serve Type 3 customers, which can tolerate short term rotating outages in 15 minute intervals.
If the power demand is 110% of available energy, circuit breakers feeding Type 3 distribution lines 1 through 100 can be opened, creating an outage. Fifteen minutes later, circuit breakers feeding distribution lines 101 through 200 can be opened, and circuit breakers feeding distribution lines 1 through 100 can be closed, restoring power.
Another fifteen minutes later, circuit breakers feeding distribution lines 201 through 300 can be opened and circuit breakers feeding distribution lines 101 through 200 can be closed. This cycle is repeated until available energy matches customer demand.
So, what does this mean for customers?
For a 10% energy shortfall, 80% of an electric utility’s customers would lose power for 15 minutes every two hours.
For a 20% shortfall, the circuit breakers feeding Type 3 distribution lines 1 through 200 would become the first group that is opened. In this case, 80% of an electric utility’s customers would lose power for 15 minutes every hour.
Stop the Use of Prolonged Outages
Short term outages in 15 minute intervals are the best way to structure rotating outages. This way, residences will not become too cold during winter weather or too hot during a heat wave. Most residential refrigerators can withstand being without power for 15 minutes without a significant drop in temperature, keeping food and medicine safe.
To effectively enact this new plan, updates must be made to the design of distribution lines so that lines specifically serve only critical infrastructure, critical industries, or residential areas. A switching device could be implemented in a substation, which would send the signal to only disrupt power from a specific residential area.
Additionally, procedures for how to effectively implement rotating outages must be developed before the outages are necessary. TSOs must be trained in how to enact a rotating outage so that they are prepared, as the need for them may arise unexpectedly. By approaching rotating outages with proactive plans in place, electric utility companies can be prepared for the next extreme weather event.
Updates to the Grid Are Necessary
Rotating outages (a.k.a. rolling blackouts) can be an effective solution when power demand exceeds power production if the appropriate plans are in place. By focusing rotating outages on residential areas, the economic impact of these outages would be significantly reduced.
The power grid needs to be fully updated to a smart grid so algorithms can be implemented, which means that TSOs will no longer manually perform rotating outages. Specific algorithms can also be developed to initiate signals that shut off specific loads rather than whole distribution lines. When that happens, rotating blackouts will no longer be necessary. Ultimately, the electric power grid must be updated for rotating outages to become a thing of the past.
To work with Prescient to develop theses algorithms, contact us directly or explore our wide area power outage prevention services.
This article was co-authored by Alyssa Sleva, Head of Marketing at Prescient.