Continuity of supply in a Swiss urban electrical network — A spatial analysis

Reliability of electrical energy is expected in modern societies and economies. In a liberalised energy market outages of electrical utilities will annoy customers much more than previously. On the other hand power companies have to reduce costs to stay competitive. Beside reducing costs the quality of the product has to be maintained. One aspect of quality is the continuity of energy supply, which is characterized by the number and duration of unplanned and planned supply interruptions. According to the CEER (Council of European Energy Regulators) second benchmarking report on quality of electrical supply [1], two types of continuity indicators are used: 1) The SAIFI (System Average Interruption Frequency Index) indicates the number of times in a year energy is not delivered to a customer and 2) the SAIDI (System Average Interruption Duration Index) indicates the duration in a year energy is not supplied to a customer. A further indicator, called CAIDI (Customer Average Interruption Duration Index), represents the average time required to restore service to the average customer per sustained interruption. The reliability of the urban network of the “Elektrizitätswerk der Stadt Zürich” (ewz) is investigated. After comparisons of SAIDI on the country- and regional-level with CEER-report results, a spatial analysis of the network, according to the areas delivered from a particular HV/MV-substation, is performed for SAIFI, SAIDI and CAIDI. In a further step, the indices are amended to consider the customer interruption costs, according to four kind of customers (residental, industrial, commercial, other) [2]. The study is restricted to the unplanned interruptions.