A bibliographic analysis of transformer literature 1990-2000

This paper presents an analysis of the bibliography on transformers covering the period from 1990 to 2000. It contains all the transformer subjects: a) Transformer design, b) Transformer protection, c) Transformer connections, d) Transformer diagnostics, e) Transformer failures, f) Transient analysis of transformers (overvoltages, overcurrents), g) Modeling and analysis of transformer using FEM (thermal modeling, losses modeling, insulation modeling, windings modeling). Several international journals were investigated including the following: Advances in Electrical and Computer Engineering, Canadian Journal of Electrical and Computer Engineering, COMPEL (The International Journal for Computation and Mathematics in Electrical and Electronic Engineering), Electrical Engineering, Electric Power Components and Systems, Electric Power Systems Research, European Transactions on Electrical Power, IEEE Transactions on Magnetics, IEEE Transactions on Power Delivery, International Journal of Electrical Power and Energy Systems, and IET Generation Transmission & Distribution. Due to the high number of publication in journals, we are not considering publications of conferences and symposia. A total of 700 publications are analyzed in this paper. The research presented in this paper is important because it contains and analyzes the best research papers on transformers coming from many countries all over the world and published in top rated scientific electrical engineering journals

Multi-port network and 3D finite-element models for accurate transformer calculations: Single-phase load-loss test

A six-port impedance network for a three-phase transformer is obtained from a 3D time-harmonic finite-element (FE) model. The network model properly captures the eddy current effects of the transformer tank and frame. Ail theorems and tools of passive linear networks can be used with the multi-port model to simulate several important operating conditions without resorting anymore to computationally expensive 3D FE simulations. The results of the network model are of the same quality as those produced by the FE program. Although the passive network may seem limited by the assumption of linearity, many important transformer operating conditions imply unsaturated states. Single-phase load-loss measurements are employed to demonstrate the effectiveness of the network model and to understand phenomena that could not be explained with conventional equivalent circuits, In addition, formal deduction of novel closed-form formulae is presented for the Calculation of the leakage impedance measured at the high and low voltage sides of the transformer. (C) 200

Asymmetry during load-loss measurement of three-phase three-limb transformers

When the load-loss measurement test is conducted on three-phase transformers, an appreciable asymmetry is observed among the power readings of the three phases. This asymmetry is the result of two causes, viz. asymmetrical disposition of phases in space with respect to each other and unequal stray losses produced by phases. The disposition of phases leads to asymmetrical mutual impedances between phases and this is the principal contributor to the phenomenon. Another factor that may have an important contribution to the phenomenon is the deviation of the phase angle difference between the voltages of the three phase source (used during the test) from 120 degrees. The causes are analyzed using a detailed three-dimensional (3-D) finite-element (FE) simulation of a 31.5 MVA, 132/33 kV transformer. In addition, a six-port network impedance model is deduced from open-circuit 3-D FE simulations. The impedance model is able to reproduce any condition of the transformer (e.g., open-circuit, short-circuit or on-load conditions) since it captures all the transformer electromagnetic phenomena. The six-port network results are discussed in order to elaborately clarify the intriguing problem of asymmetrical load-loss distribution, which is important for both transformer manufacturers and users. The results are further explained through sequence components; of currents

Analytical Description of the Load-Loss Asymmetry Phenomenon in Three-Phase Three-Limb Transformers

The asymmetry phenomenon observed during the load-loss test of three-phase transformers is rigorously analyzed. The transformer is represented as a three-port impedance network despite its six-port network nature, making any formal study more tractable. The analytical restrictions required for such a representation are derived. As a result, it is possible to mathematically prove (and understand) the asymmetrical behavior of a three-phase transformer subjected to the load-loss test. Only two circuit-field simulations or tests (single-phase load-loss tests) are required to obtain the impedance system of the six-winding transformer. A 3-D finite-element (FE) model of a transformer is used here to obtain its short-circuit impedances, exemplifying the use and extent of the analytical results. The eddy currents generated at the transformer tank and frame are properly taken into consideration. The short-circuit impedance model is validated with the 3-D FE model and with a six-port network approach that has been previously verified

Evaluation of eddy current losses in the cover plates of distribution transformers

The elimination of hot spots and the reduction of eddy current losses in bushing mounting plates is an important consideration in transformer design. The currently used bushing mounting plates are either mild steel plates, or mild steel plates with non-magnetic stainless steel inserts or stainless steel plates. The authors calculate the eddy current losses in bushing mounting plates using four different methods; (i) an analytical formulation; (ii) a three-dimensional finite element method (FEM); (iii) from measured values of the initial temperature rise; and (iv) from measured values of the steady-state temperature rise. There is a close agreement between the loss values obtained using these four methods. The analysis has resulted in a detailed understanding of the loss pattern and temperature rise phenomenon in bushing mounting plates. The authors also analyse tank plates of small pad-mounted distribution transformers. It is shown that judicious use of non-magnetic stainless steel can result in considerable energy savings for pad-mounted transformers. FEM simulations are performed to find out cost-effective materials for the tank plates of the pad-mounted transformers. A T-shaped stainless steel plate is found to significantly reduce the load loss. The results of the simulations have been verified on a 225 kVA pad-mounted transformer

Analysis of slots in horizontal plates of T-beams in shell-form power transformers

A systematic analysis of the use of slots to reduce stray losses in the horizontal plates of the T-beams in shell-form power transformers is presented. In the paper, the horizontal plate of T-beams is modeled as a rectangular stainless steel plate subjected to a perpendicular uniform magnetic field generated by a Merritt coil. The results are compared with the values given by an analytical formula for calculating the losses in a stainless steel plate without slots. The following important design alternatives are analyzed and discussed: (1) plates with rounded slots; (2) plates with unrounded slots; (3) effect of width and length of one slot; (4) effect of the distance between slots; (5) effect of number of slots. It has been found that substantial loss reduction can be obtained when drilling a few slots. Measurements of flux densities were done for seven shell-form power transformers. Using the measurements we calculated the losses in the plates using formula. Using the results of the design alternatives the efficiency of the use of slots in plates of real T-beams was demonstrated. Finally, a structural analysis was made to study the impact of slots in an experimental slotted T-beam. (C) 2013 Elsevier B.V. All rights reserved