Evaluation of distribution transformer banks in electric power systems

Abstract

SUMMARYThis article compares the total mass and the total owning cost (TOC) of three-phase distribution transformer banks with standard three-phase distribution transformers. The comparison is based on the minimum TOC. This is achieved through a field-validated distribution transformer design program that automatically minimises the objective function (TOC). In particular, 12 oil-immersed distribution transformers are designed: 6 three-phase transformer banks and 6 three-phase transformers; these designs meet all the requirements of a given transformer standard. As a result, curves of minimum TOC versus transformer rating are obtained for threephase transformer banks and three-phase transformers. Moreover, similar curves from seven transformer manufacturers are collected; the advantage of this collection is that these different manufacturers have different types of transformers: oil immersed or dry type, core or shell type, various voltage classes and power ratings, and so on, and consequently more general conclusions can be drawn regarding the comparison of three-phase transformer banks and three-phase transformers. From these investigations, it was found that from the viewpoint of minimum total mass and minimum TOC, three-phase transformer banks should be recommended in case of small-size transformers (rating lower than 45 kVA). This is an important finding that is not emphasised in recommended practices reported in transformer textbooks.

A preliminary study of transformer life estimation based on linear cumulative damage theory

“…For instance, the reference temperature for normal Kraft paper insulated transformer is 98°C (Equation ) and for thermally upgraded paper insulated transformers is 110°C (Equation ). Moreover, the design of transformers is continuously improved , which may affect the corresponding parameters. Therefore, in practical application, appropriate parameters should be selected depending on the type of the transformer.The application in electrical stress, mechanical stress, and multi‐stress is still being studied.…”

Suggested Temperature Monitoring System for Distribution Transformers by Using Microcontroller Scheme

“…So, it is essential to control the temperature within permissible limit to ensure the long-life of the transformer by reducing thermal degradation of its insulation system. In electrical power transformer, external cooling system is used to accelerate the dissipation rate of heat [10,14,17]. There are different transformer cooling methods available for oilimmersed transformers, as follows: The transformers under-study are following (O.N.A.N.)…”

Novel inrush current restraining method for transformers of shipboard power system

“…This transient current, which is several times of normal current, will cause a large voltage decrease on the connected bus and affect the normal operation of other equipment. The widely used methods for reducing the magnetizing inrush current are pre-insertion of series resistors and controlled switching [3][4][5][6][7][8][9][10][11][12][13][14]. For the star grounded connection transformer, a neutral resistor combining with a sequential phase energization scheme is proposed to limit the inrush current [10,11].…”