Service continuity and quality

Continuity is the most important parameter for measuring the performance of the electricity service. All the segments of the electric system – generation, transmission, and distribution – contribute to the final result: to ensure society the availability of electricity with outages below pre-established thresholds and with appropriate standards of technical quality.   

The tables on the following pages show Terna’s performance regarding the transmission service for which it is directly responsible. In particular, the results of the last few years and the related targets are reported, as well as the objectives for 2011.

Service continuity is also an objective recognized by the Electricity and Gas Authority (AEEG).

During 2010 the Company continued the campaign to measure the voltage data in its plants through the monitoring network in service since 2006. The campaign also included cooperation with end HV customers and the distribution companies. Devices installed in the network furnish important information on the quality of the supplies of electric power. 

AVAILABILITY INDICATOR (AVERAGE SYSTEM AVAILABILITY - ASA)

AVAILABILITY INDICATOR (AVERAGE SYSTEM AVAILABILITY - ASA)

ASA (Average System Availability)i
This measures the average availability of the electricity grid components for use in a given period. This index can be expressed with regard to specific categories (for example, by voltage level), grid areas, or – as in this case – the entire National Transmissioni Grid.
The performance achieved in 2010 exceeded the target set.

CONTINUITY INDICATOR (SAIFI + MAIFI)

CONTINUITY INDICATOR (SAIFI + MAIFI)

SAIFI+MAIFI (Short Average Interruptioni Frequencyi Index + Medium Average Interruption Frequency Index)
This interruption frequency index is calculated as the ratio between the number of customers involved in short (less than 3 minutes) and long (more than 3 minutes) interruptions and the number of users of the National Transmission Grid. The figure is rounded to the second decimal. The performance achieved in 2010 exceeded the target set. 

SYSTEM CONTINUITY INDICATOR (AVERAGE INTERRUPTION TIME – AIT)

SYSTEM CONTINUITY INDICATOR (AVERAGE INTERRUPTION TIME – AIT)

AIT (Average Interruption Time)i
The average interruption time of the electricity system (NTG) in one year is calculated as the ratio between the energy not supplied in a given period (ENS value) and the average power absorbed by the system in the period in question. The figure is rounded to the second decimal.   
The performance achieved in 2010 is in line with the target set.

SERVICE CONTINUITY INDICATOR (ENERGY NOT SUPPLIED - ENS)

SERVICE CONTINUITY INDICATOR (ENERGY NOT SUPPLIED - ENS)

ENS (Energy Not Supplied)
Until 2007 the ENS indicator was used as an internal process indicator for the purpose of improving Terna’s performance. This indicator regarded the energy not supplied to users directly connected to the NTG because of events that affected the latter and did not consider the shares that were due to significant incidents.   
With its Resolution 341/07, as from January 1, 2008 the AEEG has regulated the quality of the service provided by Terna through a mechanism based on incentives and penalties, which, among other things, revised the ENS indicator. The new index also includes the energy not supplied to directly connected users caused by events on connecting networks that are not part of the NTG and a share of the energy not supplied because of force majeure events or by Significant Events(1). The performance achieved in 2010 exceeded the target set.

(1) By “significant event” is meant any interruption with net energy not supplied exceeding 250 MWh. The share that affects the ENS index is a percentage that decreases as the energy not supplied increases during a single significant incident.