IEVref: 692-08-03 ID: Language: en Status: Standard Term: service unavailability per customer served Synonym1: system average interruption duration index, CA US [Preferred] Synonym2: SAIDI [Admitted] Synonym3: Symbol: UCS Definition: sum of durations of all interruptions of supply to individual customers served during a time interval, divided by the product of the total number of customers served and the duration of that time intervalNote 1 to entry: If tij is the duration of the ith interruption of supply to customer j during a time interval of duration T, and NS the total number of customers served, then the service unavailability per customer served is given by${U}_{\text{CS}}=\frac{{\sum }_{i}{\sum }_{j}{t}_{ij}}{{N}_{\text{S}}T}$ Note 2 to entry: Only sustained interruptions are considered. Note 3 to entry: If the duration of the time interval is expressed in years, the quantity is called the "average yearly downtime per customer served". Note 4 to entry: The term "customer" represents the end user and not some intermediate distribution system or company. Note 5 to entry: Service unavailability per customer served can be used to describe past performance or to estimate expected future performance. Note 6 to entry: This entry was numbered 191-27-03 in IEC 60050-191:1990. Publication date: 2017-12-15 Source: Replaces: Internal notes: CO remarks: TC/SC remarks: VT remarks: Domain1: Domain2: Domain3: Domain4: Domain5: