In reliability engineering, the term availability has the following meanings:
In electrical engineering, the power factor of an AC power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit. Real power is the average of the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of root mean square (RMS) current and voltage. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power, so more current flows in the circuit than would be required to transfer real power alone. A power factor magnitude of less than one indicates the voltage and current are not in phase, reducing the average product of the two. A negative power factor occurs when the device generates real power, which then flows back towards the source.
Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system. The term is used for repairable systems while mean time to failure (MTTF) denotes the expected time to failure for a non-repairable system.
In finance, the duration of a financial asset that consists of fixed cash flows, such as a bond, is the weighted average of the times until those fixed cash flows are received. When the price of an asset is considered as a function of yield, duration also measures the price sensitivity to yield, the rate of change of price with respect to yield, or the percentage change in price for a parallel shift in yields.
A golf handicap is a numerical measure of a golfer's ability, or potential ability, that is used to enable players of different abilities to compete against one another. Better players are those with the lowest handicaps.
Net run rate (NRR) is a statistical method used in analysing teamwork and/or performance in cricket. It is the most commonly used method of ranking teams with equal points in limited overs league competitions, similar to goal difference in football.
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
In economics, the Törnqvist index is a price or quantity index. In practice, Törnqvist index values are calculated for consecutive periods, then these are strung together, or "chained". Thus, the core calculation does not refer to a single base year.
An outage management system (OMS) is a computer system used by operators of electric distribution systems to assist in restoration of power.
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.
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
The poverty gap index is a measure of the degree of poverty. It is defined as extent to which individuals on average fall below the poverty line, and expresses it as a percentage of the poverty line.
The PM NowCast is a weighted average of hourly air monitoring data used by the United States Environmental Protection Agency (USEPA) for real-time reporting of the Air Quality Index (AQI) for PM (PM10 or PM2.5).
The Customer Total Average Interruption Duration Index (CTAIDI) is a reliability index associated with electric power distribution. 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:
Evaluation measures for an information retrieval (IR) system assess how well an index, search engine, or database returns results from a collection of resources that satisfy a user's query. They are therefore fundamental to the success of information systems and digital platforms.
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.
Loss of load in an electrical grid is a term used to describe the situation when the available generation capacity is less than the system load. Multiple probabilistic reliability indices for the generation systems are using loss of load in their definitions, with the more popular being Loss of Load Probability (LOLP) that characterizes a probability of a loss of load occurring within a year. Loss of load events are calculated before the mitigating actions are taken, so a loss of load does not necessarily cause a blackout.
