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Study of Nanocomposites for Electrical Insulation
Klampár, Marián ; Mentlík, Václav (referee) ; Váry,, Michal (referee) ; Liedermann, Karel (advisor)
The dissertation thesis submitted deals with the study of dielectric properties of epoxy nanocomposites containing nanoparticles of inorganic oxides. These nanocomposites may have a promising technologic application for electric insulations in view of their higher resistance against partial discharges; yet information about their behavior in the course of ageing is not available. If at least a partial mass replacement of the currently used epoxy insulation with nanocomposite-based insulations is due to occur, the knowledge of the changes of their dielectric properties in the course of their operation will become indispensable. Within the framework of this dissertation, ensembles of samples of epoxy resins without fillers and with Al2O3, WO3, TiO2 and SiO2 fillers in the form of nanopowders, in concentrations up to 12 wt %, have been prepared. These ensembles have been measured prior to ageing and exposed to long-time (up to 5000 hours) ageing at increased temperatures 200, 250 and 300 °C and in a few cases also at 330 and 360 °C. Samples were measured in the course of ageing roughly in a logarithmic time series after 1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000 and 5000 hours. The measured quantities included complex permittivity , internal resistivity i and loss factor tan at temperatures ranging from -153 °C to +167 °C and in the frequency range 10-2 – 106 Hz. Changes in nanocomposites have been investigated using not just dielectric spectroscopy measurements, but other methods, too, namely Fourier-transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The experiments have proved that materials with different fillers respond to the same concentrations of various fillers in different ways. The addition of nanoparticles, without the addition of microparticles, at a relatively low concentration (max 12 wt %), was not sufficient for reaching fundamental changes in dielectric spectrum; only smaller changes of dielectric strength and shifts of relaxations and in relaxation maps have occurred. Out of more pronounced changes, increase of concentration of the SiO2 filler in the epoxy matrix brings about a decrease of electrical conductivity in the resulting nanocomposite. The TiO2 filler had a different impact. Different TiO2 concentrations make their marked appearance in the region between the relaxation and relaxation. The TiO2-filled nanocomposites do not exhibit the unambiguous dependence of electrical conductivity on nanofiller concentration. It can be concluded that the mere addition of nanoparticles, without the addition of established microparticles, does not change the dielectric spectrum substantially. Generally, a serious problem was the production of the nanocomposite with a uniform distribution of nanoparticles. The preparation of such a nanocomposite was not trivial and, in industrial applications, this issue will require a specific focus, so as to avoid the formation of undesirable aggregates. Within the framework of this research, a methodology for the production of an epoxy nanocomposite has been developed with as high as possible uniformity of nanoparticle distribution.
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Measurement uncertainty in diagnostics of insulating materials
Kamenická, Zuzana ; Rozsívalová, Zdenka (referee) ; Frk, Martin (advisor)
This work deals with measurement capacity and dissipation factor of capacitor with real dielectric in frequency range 20 Hz to 30 MHz. Liquid and solid dielectrics are measured by LCR instruments and by test fixtures, both from company Agilent. Relative permittivity and loss number are calculated for different instruments settings. The general aim is to specify the influence of parameters as frequency, voltage, integration time and thickness of material on the uncertainties of primary and secondary quantities for measurement.
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Analysis of the properties of liquid crystalline materials
Bodeček, Martin ; Rozsívalová, Zdenka (referee) ; Frk, Martin (advisor)
Master´s thesis covers introduction to the problems of materials with specific proprieties named liquid crystals. Theoretic part features primary fission these materials, theirs mechanical, electrotechnical and optical characteristics. Interesting chapter is description choice application including perhaps most interesting using liquid crystals - liquid crystal display. In this trend continues experimental part too, where there are first mentioned characteristics LCD, and after it alone metering capacitive characteristics display with active matrix. Main attention in experiment is however concentraded on evaluation frequency analysis of components complex permittivity regarding in plant temperature on submitted sample liquid crystals.
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Study of dielectric relaxation in PCB substrates and cable insulation
Ježík, Jan ; Brzobohatý, Jaromír (referee) ; Běťák, Petr (advisor)
This study investigates relaxation polarization in some dielectric components of tester UNISPOT S40 developed by company UNITES Systems a.s. Relaxation polarization in the PCB substrates and in tester’s cable insulation causes undesirable deceleration of some test steps. Relaxation polarization in selected PCB substrates and various cables are examined by method of dielectric relaxation spectroscopy in the frequency domain and by measurement of polarization or depolarization current.
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Synergic effects of multistress ageing of electroinsulating materials
Novák, Lukáš ; Frk, Martin (referee) ; Rozsívalová, Zdenka (advisor)
Submitted work deals with monitoring impact of thermal and electric ageing on the dielectric properties of insulating material NKN 0887. In the course of the experiment five sets of dielectric insulating materials were aged. The voltage range has been set from 1,5 kV till 2,2 kV and temperatures were 23 °C and 200 °C. The capacity and loss factor has been directly measured by RLC meter Agilent with attached electrode system. The electrode system operates on the principle of a plate capacitor. The values of relative permittivity and loss number has been calculated from values of capacity and loss factor. For easier confrontation has been frequency dependences of these values plotted in a chart. The Cole-Cole diagrams has been created and factors of Havriliak-Negami function has been calculated. Data has been compared with each other and the effect of ageing factors has been deduced.
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Influence of curing parameters on the properties of insulating varnishes
Paščinský, Jiří ; Frk, Martin (referee) ; Rozsívalová, Zdenka (advisor)
The bachelor thesis submitted deals with properties of electro-insulating lacquer hardenable by ultraviolent radiation and temperature. Within the theoretical part a summary of electro-insulating lacquers used in electrotechnics has been elaborated. Chemical changes that take place in this material group have been described during hardening process. A method of dielectric relaxation spectroscopy specifically focused on mathematic and physical description of polarisation and conductive mechanisms taking place in the structure of the given material has been closely studied. In the experimental part a workplace for hardening and long-term exposition of lacquered samples during simultaneous effect of various climatic elements has been designed and built. The selected electric and mechanical properties have been monitored on three sets of experimental samples prepared by means of different methodical procedures. The results gained have been mathematically evaluated and physically interpreted in term of methodical procedure of hardening and different temperature of measurement.
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The use DC electrical method in diagnostics of insulating materials
Volf, Michal ; Rozsívalová, Zdenka (referee) ; Frk, Martin (advisor)
In this work describe to the Dielectric relaxation spectroscopy for the evaluation of the actual status of insulation systém. The used methods of quantifying the dielectric response in time domain are polarization-depolarization current and recovery voltage measurement and in frequency domain the loss factor and the complex capacitance measurement. Influence of thermal ageing and temperature dependences of charge and dischage currents are observed.
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Analysis of degradation mechanisms oligobutadienes
Baťa, David ; Rozsívalová, Zdenka (referee) ; Frk, Martin (advisor)
This work deals with the studies of liquid oligobutadiens properties in AC electric field by dielectric relaxation spectroscopy method. The current issue in the diagnosis of oligomeric and polymeric materials during the activity of various degradation factors and options of their alleviation and suppression was studied. The existing apparatus is modified for monitoring possibilities of polymeric materials during the action of various degradation and operational factors. Effect of climatic factors are experimentally investigated, especially UV radiation and temperature on the course of the frequency dependence of complex permittivity components with respect to the different composition and length of the polymer chain.
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