Technical and Economic Criteria for Selection of Transformer Power in Distribution Circuits

Abstract

When selecting transformer power at the design stage, it is necessary to quantify the reliability and service life of the electrical equipment, as well as the cost efficiency of the construction of power supply system. This issue is especially relevant for 6–10 kV distribution circuits, since a significant part of the substations of this voltage class is on the balance sheet of consumer who bear the costs for the design, construction and operation of these substations. The service life of a transformer, as well as high and low voltage devices of substations, depends on the voltage class, operating conditions, the operation of electrical power equipment in normal and emergency modes, and the load factor of a transformer in various operating modes. The paper considers the technical and economic criteria for selection of an oil-immersed transformer for outdoor unitized transformer substations with a voltage of 6–10 kV, the reasons of reducing its service life, the influence of the load factor of a transformer on the wear of insulation and the reduction of the service life of its safe operation. The methods and results of calculation of the relative service life of a transformer depending on the load factor are given. The criteria for selection of the load factor are determined depending on the capacity, structure and type of consumers of electricity.