Impact of power transformer failures on customer interruptions costs using customer damage functions

Abstract

Electrical power is essential in the operation, development, and economy. Depending on their activities, the loads can be classified into five main sectors; industrial, agricultural, commercial, governmental, and residential. Various load sectors are affected by power interruptions which are translated into Customer Interruption Costs (CICs). These costs depend on the class of the load sector, and the interruption duration. Load interruptions can be attributed to lack in the power production and/or failures in various components in the power grid, and supply system. This paper focuses on the impact of failures of power transformers on CICs considering various voltage populations in the Egyptian utility grid. In addition, the impacts of the failures in various subassemblies in power transformers, and other outage causes on CICs are presented. The CIC estimation method is based on combining the Customer Damage Functions (CDFs) of various load sectors into one damage function which is the Composite Customer Damage Function (CCDF). The CCDF is obtained through weighting of the CDFs of various load sectors where the weighting factors are the percentage of various load sectors comprising the load mix composition. In addition, the impact of the interruption durations on the CCDF is considered through the consideration of the interrupted power, and interrupted energy. The determined CCDF is approximated to an algebraic function through curve fitting. The interruptions data of power transformers are obtained from a long term survey of power transformer failures for eight years from years 2002 to 2009 at various locations, and voltage populations in Egypt based on Egyptian Electricity Transmission Company (EETC) surveys. The Customer Damage Functions (CDFs) of various load sectors are obtained from a previous study. The results show the severity of failure in various subassemblies of power transformers in various voltage subpopulations. Therefore, the presented results can contribute in enhancing maintenance schedules, and manufacturing of power transformers as well as estimating the CICs.