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- 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.
- 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.
- 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.
- Detection of trasformer intermittent winding faults by the on-load exciting current Park`s vector approachPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper presents the application of the on-load exciting current Park's Vector Approach for diagnosing permanent and intermittent turn-to-turn winding faults in operating power transformers. First, an experimental investigation of the behaviour of the transformer under the occurrence of both permanent and intermittent winding faults is presented. Finally, experimental test results demonstrate the effectiveness of the proposed diagnostic technique, which is based on the on-line monitoring of the on-load exciting current Park's Vector patterns.
- Three-phase, three-limb, steady-state transformer modelPublication . Oliveira, L. M. R.; Cardoso, A. J. MarquesThis paper presents the development and implementation of a digital simulation model of a threephase, three-leg, three-winding power transformer. The proposed model, implemented in MATLAB environment, is based on the simultaneous analysis of both magnetic and electric lumped-parameters equivalents circuits, and it is intended to study its adequacy to incorporate, at a later stage, the influences of the occurrence of windings interturn short-circuit faults. 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.
- Diagnóstico de avarias em transformadores trifásicos em serviço através da análise do Vector de Park das correntes de excitação em cargaPublication . Cardoso, A. J. Marques; Oliveira, L. M. R.Devido ao seu custo e importância estratégica, os transformadores de potência constituem um componente vital dos sistemas de produção, transmissão e distribuição de energia eléctrica. A sua fiabilidade constitui assim um factor crucial no funcionamento dos sistemas eléctricos de energia. Não admira, pois, que sobre estes equipamentos recaiam grandes preocupações relativamente à sua manutenção e, consequentemente, ao desenvolvimento de métodos capazes de fornecerem um diagnóstico completo e fiável do seu estado de funcionamento. Para o efeito, torna-se porém indispensável possuir um conhecimento detalhado acerca das avarias susceptíveis de ocorrerem nos transformadores, bem como dos mecanismos específicos que lhe estão subjacentes.
- Transformers on-load exciting current Park`s vector approach as a tool for winding faults diagnosticsPublication . Oliveira, L. M. R.; Cardoso, A. J. Marques; Cruz, S. M. A.This paper presents the development of a new approach for diagnosing the occurrence of inter-turn short-circuits in the windings of three-phase transformers, which is based on the on-line monitoring of the on-load exciting current Park's Vector patterns. Experimental and simulated results demonstrate the effectiveness of the proposed technique for detecting winding inter-turn insulation faults in operating three-phase transformers.