The paper describes the FASIT standard for reliability data collection, and reliability indices calculation and reporting. Such standards are necessary as a basis in quality of supply regulation, particularly for the documentation of existing levels of reliability of supply, and for providing input data to the value-based reliability planning. The structure and specification of FASIT is thoroughly described in the paper.

The strong focus on global warming the recent years has contributed to a change towards a more climate friendly and energy efficient energy system. New energy efficient electrical appliances have clearly shown to be a challenge in the Norwegian distribution system and in the low voltage network in particular. These types of electrical loads have shown to increasingly often cause voltage disturbances exceeding the quality limits in both the EN50160 [1] and the Norwegian voltage quality regulations [2]. This have shown to cause everything from only irritation among customers based on poor lighting quality to malfunction and trip of electrical equipment. Estimates made by Norwegian network operators indicate that the necessary network reinforcement investments in Norway are in the range 2 to 12 billion Euros if all customers are being allowed to install and use the most challenging electrical appliances. These challenges will probably be similar in other countries if not necessarily as large as in Norway. Performed investigations indicate a high percentage of low voltage networks in Norway with relatively low short circuit capacity as between 40 and 50 % of the low voltage networks seem to have a higher impedance than the European reference impedance. Norwegian Distribution System Operators (DSOs) are raising the question whether all electric appliances should be treated as "normal" equipment that can be used unconditionally or whether there is a need for changes in the rules for what equipment the DSOs must be notified about before the load is connected and used.

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