A Method for Estimating the Frequency and Cost of Voltage Sags

The annual number and cost of voltage sags were determined for five Finnish distribution companies. The method of fault positions was applied for the calculation of voltage sag frequency. The economic consequences were assessed by multiplying the sag frequency and cost by the number of customers. The cost of a single sag was taken from a survey that had been carried out in three Nordic countries in the mid 1990s. The paper proposes a method for retrieving sag-related information from statistics originally prepared for other purposes. In addition, the paper provides an estimate of the total annual sag-related cost for each of the companies considered in this study and for each customer category. The total cost per company appeared to be much higher than had generally been assumed.