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Electric Reliability Explained

Why we're keeping track

Do you know what percent of time your power was available and functioning like normal last year? The answer is about 99.97% of the time, according to EWEB’s 2022 metrics on outage occurrences and length of outages. That means 99.97% of the time you could turn on the lights, heat or cool your home, get hot water out of the tap, run your appliances, watch TV, charge your phone, and do the hundreds of other things we all do every day with electricity.

When electricity is so reliable and accessible with a simple flip of the switch, it can be easy to overlook what it takes to maintain a reliable electric grid. Utility infrastructure is a complex system that requires investment and maintenance to provide constant, reliable power.

As your community-owned utility, we want you to be satisfied with the electricity you receive and the rate you pay for it. That’s why we track how our electric grid performs to make sure you’re receiving the most reliable service for the dollars you're investing when you pay your monthly electric bill. Tracking and monitoring electric outages helps us prioritize investments in infrastructure and equipment upgrades and allows us to report to our customer-owners regarding the quality of service you are receiving.

The two metrics we rely on are common in the electric utility industry – average duration of outages and average frequency of outages.

Average Duration of Outages

We keep track of the average duration of outages in minutes per customer. Commonly referred to as System Average Interruption Duration Index (SAIDI). To calculate this metric, we divide the total minutes customers were without power by the number of all EWEB customers.

2022 EWEB SAIDI Metric = 62.22 (average duration in minutes for an EWEB outage)

Approximately one hour was the average duration of a power outage last year. When you consider the process that goes into responding to and restoring power, that’s a relatively short amount of time. Crews must troubleshoot, coordinate response, and repair any issues before power can be restored. This average duration is thanks to the quick, efficient, and safe work performed every day (and night) by EWEB’s electric crews.

Average Frequency of Outages

We keep track of the average frequency of power outages. Commonly referred to as System Average Interruption Frequency Index (SAIFI). To calculate this metric, we divide the total number of interruptions per impacted customers by the total number of EWEB customers.

2022 EWEB SAIFI Metric = 0.475 (average number of outages experienced per EWEB customer)

Power outages can be unpredictable. Animals, auto accidents, vegetation, extreme weather conditions and equipment failure can all play a role in a power outage. While we can’t control the weather or the squirrels, we can invest in replacing aging infrastructure to maintain system reliability and avoid equipment failure, reducing the number of outages experienced by customers.

Delivering reliable power

Just as many factors can cause a power outage—most often weather, vehicle crashes, equipment failure, and wildlife—there are many pieces that come together to deliver power that is 99.97% reliable. The electricity infrastructure must be sufficient to handle the demand placed on it. This includes having enough power plants, transmission lines, and substations to supply electricity to customers. In addition, the infrastructure must be maintained through routine inspections and repair or replacement of worn or damaged equipment.

The availability of skilled personnel is also an essential factor in ensuring reliable electricity. Building and maintaining the grid requires skilled professionals such as engineers, software and cybersecurity technicians, and electric line technicians.

The reliability we have today is also thanks to those who planned, built, and paid for a such robust system during an infrastructure boom approximately 60 years ago when Eugene was rapidly expanding.

“It’s amazing how the investments of EWEB customers in the 1960s and 1970s still serve us today,” said Philip Peterson, EWEB systems engineer, and the lead engineer on the Currin Substation rebuild project. “But in the last few years, especially, we’ve seen a noticeable uptick in equipment failures at the substation level. It’s time for us to rebuild and reinvest for the benefit of future generations, while also making sure our equipment meets modern standards.”

The rates you pay as a customer today are being invested into a new era of EWEB’s electric infrastructure which will ensure we meet the current and future needs of our community, while maintaining reliable service for the next half a century and beyond. 

Comparing apples to apples

To put this data in perspective, we compared our 2021 metrics and 2022 average customer electricity rates with a few other utilities in the Pacific Northwest. Here you can see the value of your dollars reflected in the reliability of the electricity EWEB brings to your home or business.

Remember, the lower the average number reflected for frequency of outages and duration of outages means the higher the reliability for the electricity delivered.

Additional Information

The Equations


 SAIDI – Let’s say a fuse blew, de-energizing a tap that feeds power to 10 customers and it takes 50 minutes to fix the problem and restore power and the utility has 10,000 customers. To calculate the SAIDI metric, we would do the following equation: 10 customers multiplied by 50 minutes divided by 10,000 customers =  0.05 (interruption in minutes).

SAIFI – Let’s say a utility of 10,000 customers had 1 outage last month where 500 customers were out of power. To calculate the SAIFI metric, we would use the following equation: 1 outage multiplied by 500 customers divided by 10,000 customers = 0.05 (frequency of power interruption per customer).

Learn more about EWEB's major infrastructure investment projects for maintaining electric reliability.