SAIFI

{{Short description|Measure of frequency of electric power interruptions}}

The System Average Interruption Frequency Index (SAIFI) is commonly used as a reliability index by electric power utilities. This index measures the average number of times that a system customer experiences an outage during the year or during a given time period.{{cite web |last1=Layton |first1=Lee |title=Electric System Reliability Indices |url=http://www.egr.unlv.edu/~eebag/Reliability_Indices_for_Utilities.pdf |website=www.egr.unlv.edu |date=2004}}

SAIFI is normally calculated on either yearly or monthly basis. SAIFI is calculated as:

$\backslash mbox\{SAIFI\}\; =\; \backslash frac\{\backslash sum\{\backslash lambda\_i\; N\_i\}\}\{\backslash sum\{N\_i\}\}$

where $\backslash lambda\_i$ is the failure rate and $N\_i$ is the number of customers for location $i$. In other words,

$\backslash mbox\{SAIFI\}\; =\; \backslash frac\{\backslash mbox\{total\; number\; of\; customer\; interruptions\}\}\{\backslash mbox\{total\; number\; of\; customers\; served\}\}$

Many factors cause power interruptions, including weather, vegetation patterns, and utility practices. Utilities can report interruption duration values with major events (such as snowstorms or hurricanes), without major events, or both.{{Cite web|url=https://www.eia.gov/todayinenergy/detail.php?id=45796|title=U.S. Power Customers Experienced an Average of Nearly Five Hours of Interruptions in 2019 |date=2020-11-06 |website=US Energy Information Administration|language=en|access-date=2025-01-30}}

SAIFI is measured in units of interruptions per customer.

According to IEEE Standard 1366-1998 the median value for North American utilities is approximately 1.10 interruptions per customer.{{not in source|reason=AFAIL the standard provides some example, never stating that this is the actual data for some grid|date=January 2025}}