Supply Availability and Reliability

Reliability is one of the core KPI factor which shape customer satisfaction. Customers' perceptions of reliability are actually shaped through a combination of factors, involving voltage features. Therefore, the most visible of these are the continuity of supply factors in which manifest themselves in outages, be they momentary or extended. Therefore, they might be the most significant of the customer service KPIs under the control of the management of distribution companies.

Main Features

The major points associated to measuring and regulating continuity of supply are:

• The type of interruption: Planned or unplanned interruptions. Planned interruptions that are not notified might be recorded as unplanned interruptions.

• The duration of each interruption: Short or long interruptions. For instance, any interruption in which lasts more than ten minutes as a long interruption.

• The voltage levels of faults and other causes of interruptions: Low/medium/high voltage. The interruption of supply to final customers could originate at any voltage level in the system. Customers linked to low voltage networks (i.e., 1 kV) are affected by interruptions because of faults in low voltage, medium voltage (MV) and high voltage (HV) networks and transmission networks, although users connected to MV networks are not affected through interruptions due to faults in the LV network. In HV and transmission networks, not all faults cause interruptions to final customers, because of network design.

• The type of continuity indicators i.e., number or duration of outages. The cumulative yearly duration of interruption per customer, commonly referred to as the System Average Interruption Duration Index (SAIDI) indicates how long during the year energy not supplied (average per customer) is.

The number of outages per customer in a year, termed System Average Interruption Frequency Index (SAIFI), implies how several times in a year energy is not supplied. Some customers are more sensitive to the cumulative duration while others are more sensitive to the frequency of outages.