We are entering an energy intensive world. It is very important to keep track of the energy utilized by the consumers so that necessary action can be taken to optimize it’s usage. There are various reliability indices which help us in determining the efficiency of distribution system.

**SAIFI**

SAIFI is the average number of sustained interruptions per consumer during the year. It is the ratio of the annual number of interruptions to the number of consumers.

SAIFI = (Total number of sustained interruptions in a year) / (Total number of consumers)

**SAIDI**

SAIDI is the average duration of interruptions per consumers during the year. It is the ratio of the annual duration of interruptions (sustained) to the number of consumers. If duration is specified in minutes, SAIDI is given as consumer minutes.

SAIDI = Total duration of sustained interruptions in a year / total number of consumers

**CAIFI **

CAIFI is the average number of interruptions for consumers who experience interruptions during the year. It is the ratio of the annual number of interruptions to the number of consumers affected by interruptions during the year. Consumer is counted only once regardless of the number of interruptions.

CAIFI = Total number of sustained interruptions in a year/Total number of consumers affected.

**CAIDI**

CAIDI is the average duration of an interruption, calculated based on the total number of sustained interruptions in a year. It is the ratio of the total duration of interruptions to the total number of interruptions during the year.

CAIDI = Total duration of sustained interruptions in a year/total number of interruptions.

**MAIFI**

MAIFI is the average number of momentary (less than 5 minutes) interruptions per consumer during the year. It is the ratio of the annual number of momentary interruptions to the number of consumers.

MAIFI = (Total number of momentary interruptions in a year ) / (Total number of consumers)

The above indices are the commonly used parameters used to judge the reliability for electricity generation, transmission and distribution. These outage indices are based on the duration of each power supply interruption & the frequency of interruption. It is clear that all three major functional components of the power system – generation, transmission & distribution contribute to reliability.

IoT and monitoring of electrical parameters enables to keep track of the various energy parameters which can be used to further judge the reliability of electricity distribution. The tariff can be adjusted according to this reliability indices. It would be a win-win situation for the all the stakeholders in electricity domain. Also, the end consumers will be benefited and charged according to the quality of power delivered. It would be a step towards Electricity 4.0.