Stefan Busoi - Academia.edu (original) (raw)

Papers by Stefan Busoi

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Spectroscopia în domeniu timp reprezintă una dintre cele mai eficiente metode de evaluare a compo... more Spectroscopia în domeniu timp reprezintă una dintre cele mai eficiente metode de evaluare a comportării dielectricilor in câmp electric. Funcţia de răspuns dielectric, obţinută prin măsurarea curentului de resorbţie la aplicarea unei tensiuni treaptă, permite calculul componentelor permitivităţii şi conductivităţii complexe a dielectricului în câmpuri armonice. În această lucrare, este prezentat un studiu privind calculul componentelor permitivităţii relative ( ' r ε şi ' ' r ε ), a componentelor conductivităţii complexe ( ' σ şi ' ' σ ) şi a factorului de pierderi tgδ, pornind de la curbele de variaţie în timp ale funcţiei de răspuns dielectric. Valorile calculate ale mărimilor ' r ε , ' ' r ε , tgδ, ' σ şi ' ' σ sunt verificate prin măsuratori cu ajutorul unui spectrometru dielectric Novocontrol. Toate mărimile analizate prezintă variaţii importante cu durata de îmbătrânire şi cu frecvenţa de măsurare. În final, se analizează avantajele utilizării spectroscopiei în domeniu timp în evaluarea stărilor izolaţiilor. Time domain spectroscopy is one of the most efficient methods used to assess the dielectrics' behavior under electric fields. The dielectric response function, obtained using resorption current measurement when a step voltage is applied, allows the components of complex permittivity and conductivity calculation under harmonic fields. In this paper, a study regarding the calculation of complex relative permittivity ( ' r ε and ' ' r ε ), conductivity components ( ' σ and ' ' σ ) and loss factor (tgδ), starting from time variation curves of dielectric response function, is presented. The calculated values of the quantities ' r ε , ' ' r ε , tgδ, ' σ and ' ' σ are verified by measurements performed using a Novocontrol dielectric spectrometer. All the analyzed quantities show important variations with ageing time and electric field frequency. Finally, the advantages of using time domain spectroscopy to assess the insulators conditions are analyzed.

The influence of temperature and electric field frequency on the dielectric properties of electrical machines insulation systems

… (ISEEE), 2010 3rd …, Jan 1, 2010

Electrical machines' composite insulations conditions can be characterized by the values of the d... more Electrical machines' composite insulations conditions can be characterized by the values of the dielectric properties. In this paper, an experimental study of the variation of these properties with temperature and applied electric field frequency are presented. The tests were done on plane samples and bars containing CALMICAGLAS, made of glass texture (13 %), mica paper (47 %) and epoxy resins (40 %). After their conditioning (48 h at 190 °C), real and imaginary parts of the complex permittivity and conductivity - for electric field frequencies varying from 10-3 to 106 Hz and temperatures between 30 and 90 °C - were measured using a NOVOCONTROL dielectric spectrometer. The results show important increases of the measured values with small frequency and increased temperature values. Finally, the possibility of characterizing the electrical machines insulations degradation conditions based on dielectric properties measured at low frequencies (10-3-106 Hz) is analyzed.

Rev. Roum. Sci. Tech.– …, Jan 1, 2010

In this paper, an analysis of degradation processes influence on the increase of polar products a... more In this paper, an analysis of degradation processes influence on the increase of polar products and charge carriers concentration, and the values and forms of absorption/resorption currents curves are presented. Based on their values, the polarization index and conductivity factor are determined and lifetime duration curves are drawn. Finally, it is shown that the obtained lifetime values are very close to the ones determined using the mass loss method, and the possibility of the absorption/resorption (A/R) currents use to estimate lifetime values for composite insulations of high power electrical machines is also discussed.

Calculation of insulation systems wear of medium power electrical machines

Advanced Topics in …, Jan 1, 2011

Normal operation of electrical machines and equipment is conditioned, among others, by the insula... more Normal operation of electrical machines and equipment is conditioned, among others, by the insulation systems status. Therefore, diagnosing insulation systems in order to estimate their lifetime reserve is very important, both for new equipment and especially for those in operation. This paper presents a lifetime calculation of a medium power electrical machine, whose operating cycle is known. For this purpose, the thermal lifetime curve of the machine's Calmicaglas insulation was experimentally determined; by using the Arrhenius equation, the coefficient values corresponding to the curve were calculated, followed by the total wear and remaining lifetime of the tested machine.

… of World Academy …, Jan 1, 2009

Degradation of polymeric insulation systems of electrical equipments increases the space charge d... more Degradation of polymeric insulation systems of electrical equipments increases the space charge density and the concentration of electrical dipoles. By consequence, the maximum values and the slopes of absorption/resorption (A/R) currents can change with insulation systems ageing. In this paper, an analysis of the nature of the A/R currents and the importance of their components, especially the polarization current and the current given by the space charge, is presented. The experimental study concerns the A/R currents measurements of plane samples (made from CALMICAGLAS tapes), virgin and thermally accelerated aged. The obtained results show that the ageing process produces an increase of the values and a decrease of shapes of the A/R currents. Finally, the possibility of estimating insulations ageing state and lifetime from A/R currents measurements is discussed.

The use of conductivity factors for estimating the degradation state of insulation systems of medium-power electrical machines

The use of absorption/resorption currents to characterize the ageing state of electrical equipmen... more The use of absorption/resorption currents to characterize the ageing state of electrical equipmentspsila insulation systems is well known. The maximal values and the slopes of these currents give important information regarding the paper-oil insulations for power transformers and energy cables, but these are also used for insulation systems of medium and/or high power machines. In general, the values of the conductivity factors are rarely used.