Dielectric characterization of bi-axially oriented polypropylene insulations

Recent advancement in the field of thin film polymer insulations have brought limelight in the usage of bi-axially oriented dielectric thin films for high voltage capacitors and insulations. The reason of this popularity and extensive acceptance of bi-axially oriented thin films is their peculiar characteristics and optimum balance in the thermal, electrical and mechanical properties. Moreover, the demand of high energy density for capacitors and operation of dielectrics near breakdown voltage further prominent the importance of bi-axially oriented thin films as a dielectric material and insulation. In this thesis, the dielectric material under consideration is bi-axially oriented polypropylene (BOPP) thin film and its nanocomposite. BOPP has low dielectric loss with permittivity around 2.2 and relatively high energy density because of the ability to operate near breakdown voltage because of self-healing property when used with in metallized electrodes.
The focus of this thesis is to establish the optimum procedure of sample preparation of BOPP dielectric films for dielectric spectroscopy using Novocontrol device. It has been observed that thin film or the considered material behavior and characteristics vary with respect to the physical condition and potential stresses during experiments. Thus, to min-imize these stresses, various methods have been tried by varying different physical pa-rameters which are discussed in detail in chapter 5. An optimum testing procedure has also been proposed for precise experimental results. A detailed portion on estimating reliability and repeatability of the measurements has been introduced which tries to es-tablish the validity of measurements and comment on the possible sources of errors and uncertainties.
After establishing the testing procedures, the next phase of the thesis includes the die-lectric characterization of BOPP and its nanocomposite. Since BOPP thin films can be customized by altering the polymer material composition resulting in nanocomposite and micro composites. The comparison of nanocomposites with respect to pure BOPP has also been made and explained. The effect of moisture and ambient humidity has been analyzed at different levels of relative humidity e.g. 0%, 30%, 75%, 90% and 100% RH. The degradation of the dielectric properties of polymer due to moisture absorption is studied in Chapter 6. This chapter is also comprised of dielectric behavior of BOPP and its nanocomposite as a function of temperature, frequency and applied field. The operation of pure BOPP and its nanocomposite has been studied over a temperature range of -60°C to 130°C. Moreover, the aging of BOPP w.r.t temperature has been ana-lyzed. The degradation of dielectric properties of thin film sample due to continuous application of wide range of temperatures from -60°C to 130°C during temperature test has also been observed and discussed. This aspect has been identified when these results were compared with the results found during the application of only a certain tempera-ture and not a series of different temperatures. The last phase of the thesis includes the dielectric response of BOPP as a function of applied field as the energy density and voltage endurance are of prime importance these days in high voltage applications.