The Customer Total Average Interruption Duration Index (CTAIDI) [1] is a reliability index associated with electric power distribution.[ citation needed ] CTAIDI is the average total duration of interruption for customers who had at least one interruption during the period of analysis, and is calculated as:
where is the number of customers and is the annual outage time for location , and is the number of customers at location that were interrupted. In other words,
CTAIDI is measured in units of time, such as minutes or hours. It is similar to CAIDI, but CAIDI divides the total duration of interruptions by the number of interruptions whereas CTAIDI divides by the number of interrupted customers. When CTAIDI is much greater than CAIDI, the service outages are more concentrated among certain customers.
CTAIDI also has the same numerator as SAIDI, but SAIDI divides the total duration of interruptions by the total number of customers served. The fraction of distinct customers interrupted illustrates the relationship between several reliability indicators:
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The System Average Interruption Duration Index (SAIDI) is commonly used as a reliability index by electric power utilities. SAIDI is the average outage duration for each customer served, and is calculated as:
The System Average Interruption Frequency Index (SAIFI) is commonly used as a reliability index by electric power utilities. SAIFI is the average number of interruptions that a customer would experience, and is calculated as
The Customer Average Interruption Duration Index (CAIDI) is a reliability index commonly used by electric power utilities. It is related to SAIDI and SAIFI, and is calculated as
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An outage management system (OMS) is a computer system used by operators of electric distribution systems to assist in restoration of power.
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The Momentary Average Interruption Frequency Index (MAIFI) is a reliability index used by electric power utilities. MAIFI is the average number of momentary interruptions that a customer would experience during a given period. Electric power utilities may define momentary interruptions differently, with some considering a momentary interruption to be an outage of less than 1 minute in duration while others may consider a momentary interruption to be an outage of less than 5 minutes in duration.
The Customer Average Interruption Frequency Index (CAIFI) is a popular reliability index used in the reliability analysis of an electric power system. It is designed to show trends in customers interrupted and helps to show the number of customers affected out of the whole customer base.
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The Average Service Availability Index (ASAI) is a reliability index commonly used by electric power utilities. ASAI is calculated as
The Average Service Unavailability Index (ASUI) is a reliability index commonly used by electric power utilities. It is calculated as
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Reliability index is an attempt to quantitatively assess the reliability of a system using a single numerical value. The set of reliability indices varies depending on the field of engineering, multiple different indices may be used to characterize a single system. In the simple case of an object that cannot be used or repaired once it fails, a useful index is the mean time to failure representing an expectation of the object's service lifetime. Another cross-disciplinary index is forced outage rate (FOR), a probability that a particular type of a device is out of order. Reliability indices are extensively used in the modern electricity regulation.