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- Parameters determination for the coupled electromagnetic transformer model, with particular reference to winding faults studiesPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesIn the past few years, a considerable research effort has been devoted to the development of transformer digital models in order to simulate its behaviour under transient and abnormal operating conditions. Although many three-phase transformer models have been presented in the literature, there is a surprisingly lack of studies regarding the incorporation of winding faults. This paper presents a coupled electromagnetic transformer model for the study of winding inter-turn short-circuits. Particular attention will be given to the model parameters determination, for both healthy and faulty operating conditions. Experimental and simulation test results are presented in the paper, demonstrating the adequacy of the model as well as the methodologies for the parameters determination.
- Condition monitoring and diagnostics of power transformersPublication . Cardoso, A. J. Marques; Oliveira, L. M. R.This paper addresses the subject of condition monitoring and diagnostics of power transformers. The main results of two reliability surveys, carried out under the auspices of CIGRE and IEEE in order to assemble objective data on the performance of transformers in service, are presented, providing useful information on the main causes of transformer failures, the most likely affected components and the related outages times. A survey of the most important methods, actually in use, for condition monitoring and diagnostics of power transformers is also given, which stresses the need for the development of new diagnostic methods, that can be applied without taking the transformers out of service, and that can also provide a fault severity criteria, in particular for determining transformers windings integrity. Preliminary results, concerning the on-going research activity on the development of a new approach for inter-turn winding fault diagnosis in three-phase transformers, are also reported in the paper.
- A coupled electromagnetic transformer model for the analysis of winding inter-turn short-circuitsPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper presents the development and implementation of a coupled electromagnetic transformer model for the simulation of three-phase power and distribution transformers affected by the presence of winding inter-turn short-circuits. Generically, the coupled electromagnetic transformer model is based on the simultaneous consideration of both magnetic and electric equivalent circuits. To incorporate the internal faults in this model a suitable equivalent circuit of the faulty winding is proposed. Both simulation and laboratory tests results are presented in the paper, which demonstrate the adequacy of the proposed model.
- On-line diagnostics of transformer winding insulation failures, by Park`s vector approachPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper presents a non-invasive approach for diagnosing winding insulation failures in three-phase transformers, which is based on the on-line monitoring of the primary and secondary current Park's Vector. Experimental and simulated results demonstrate the effectiveness of the proposed technique, for detecting winding inter-turn insulation faults in operating three-phase transformers.
- Incipient turn-to-turn winding fault diagnosis of power transformers by the on-load exciting current Extended Park`s Vector ApproachPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper presents the application of the on-load exciting current Extended Park's Vector Approach for diagnosing incipient turn-to-turn winding faults in operating power transformers. Experimental and simulated test results demonstrate the effectiveness of the proposed technique, which is based on the spectral analysis of the AC component of the on-load exciting current Park's Vector modulus.
- A permeance-based transformer model and its application to winding interturn arcing fault studiesPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper investigates the behavior of power transformers under the occurrence of permanent or intermittent winding insulation faults.
- Application of Park's power components to the differential protection of three-phase transformersPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper presents a new scheme for power transformers differential protection, in which the concept of the Park's instantaneous differential powers is introduced. The proposed method is able to detect winding insulation failures and to distinguish them from magnetizing inrush current transients. Experimental and simulation results are presented and discussed.
- Modelling and simulation of three-phase power transformersPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper presents the development and implementation of a digital simulation model of a three-phase, three-leg, power transformer. The proposed model, implemented in MATLAB environment, is based on the physical concept of representing windings as mutually coupled coils, and it is intended to study its adequacy to incorporate, at a later stage, the influences of the occurrence of windings inter- turn short-circuits. Both simulation and laboratory tests results, obtained so far, for a three-phase, 6 kVA transformer, demonstrate the adequacy of the model under normal operating conditions.
- Power transformers behavior under the occurrence of inrush currents and turn-to-turn winding insulation faultsPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper intends to provide a detailed characterization of the transformer behavior under the influence of inrush currents and/or incipient winding faults. Experimental and simulation results are presented and discussed. Finally, a promising new method to identify inrush currents, and to distinguish them from internal faults, is suggested.
- Power transformers' fault diagnostics by Park’s Vector ApproachPublication . Cardoso, A. J. Marques; Oliveira, L. M. R.The electricity market was, for a long time, dominated by national or regional monopolies. During the last decades, this picture has changed drastically, particularly in Europe and in the United States. The trend toward free competition and privatization with the related demands on return on investments results in a cost consciousness among utilities. In this context, monitoring and on-site diagnostics are seen as a possible way of optimizing existing assets. The main driving forces are to reduce maintenance costs, to prevent forced outages with the related consequential costs, and to work existing equipment harder and longer [1]. Transformers constitute the largest single component of the transmission and distribution equipment market.
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