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Abstract In recent years, paper has been used as an alternative to traditional substrate materials in the development of strain sensors and accelerometers due to its flexibility, disposability due to environment low footprint and low cost. A lack of knowledge about the sources of nonlinearity in the mechanical behavior of paper makes difficult to consistently predict its performance. The characterization procedures available in the literature are based on both static and dynamic loading as a first attempt to describe the elastic behavior of paper in sensing applications. However, these procedures do not reveal the necessary information to describe the elastic behavior of paper under dynamic excitation. In this work, the nonlinear dynamic response of a harmonically excited paper-based cantilever beam is studied. A lumped model with a quadratic nonlinearity is adopted to describe the nonlinear response of paper-based cantilever beams. The obtained results show that the nonlinear resonance frequency response is dependent on the intrinsic properties of paper when discarding hygrothermal variations of paper as the main source of nonlinear behavior. It was found that the estimation of two nonlinear elastic parameters, α p (hysteresis nonlinear parameter) and E 0 (linear elastic modulus) could yield an improved description of the elastic behavior of paper subjected to vibrations. It was concluded that the existing paper characterization standards should be adapted to better predict the dynamic behavior of paper-based mechanical systems. Different types of paper materials were analyzed to study the influence of the intrinsic characteristics of paper on the nonlinear parameters. Highlights • The inherent characteristics of paper are the source of nonlinear vibration. • Paper can be modeled as a lumped parameter stiffness model with quadratic nonlinearity. • The standard T535-om96 is not suitable to characterize paper based systems. • Porosity has no apparent influence on the nonlinear parameters obtained. • Nonlinear dynamic behavior can be influenced by the filler and fiber types. [ABSTRACT FROM AUTHOR]

Dielectric response techniques have been proven useful for evaluating the moisture content (Km.c) of oil‐paper insulation. However, an accurate model for oil‐paper condenser bushing has not been presented. This study designed a laboratory oil‐impregnated paper (OIP) bushing model to simulate moistened defects in oil‐paper bushings. Moreover, a 10 kV OIP bushing model was simulated using COMSOL multiphysics AC/DC to confirm that the distribution of potential meets the design requirements. Furthermore, this work investigates the effect of moisture content on the dielectric frequency response and polarisation and depolarisation current (PDC) of models of oil‐paper bushings. A group of characteristic parameters was extracted from the dielectric dissipation factor curves and the DC conductivities of different moisture contents were computed by charge difference method from PDC curves. The obtained results suggest that the dissipation factor and the capacitance increase with the increase of moisture content in the whole frequency range, and the quantitative relationships among the characteristic parameters, DC conductivities, and the moisture content were established and follow an exponential law. [ABSTRACT FROM AUTHOR]

In this paper, the influence of partial discharges (PD) on the subsequent dielectric properties of oil-impregnated paper (OIP) is investigated. Dielectric frequency response (DFR) of OIP is investigated at varied levels of moisture, thermal aging, temperature, oil conductivity and electrode material, to allow comparison of these influences. It is shown that PD activity inside OIP can significantly change the real and imaginary parts of permittivity of the paper layers, especially in the frequency range below 100 Hz. It is shown that even if the PD activity is concentrated on a few percent of the test sample, the real part of permittivity measured on the entire sample after a few tens of hours of PD activity can increase up to 10 times at very low frequencies (∼ 1 mHz) and the imaginary part of the permittivity can increase up to 100 times at low frequencies (∼ 1 Hz). The change of the real and imaginary parts of permittivity due to PD activity is permanent. It is very similar to the change caused by thermal aging, and somewhat similar to the change caused by moisture and higher oil conductivity. It is also shown that the dissipation factor of OIP in contact with copper and brass increases, even in the absence of PD, but contact with aluminum and stainless steel has no influence on DFR of OIP. The results suggest that the influence of PD can be significant when estimating the moisture content or the level of thermal aging of OIP with DFR method. [ABSTRACT FROM PUBLISHER]

Increased moisture content within an oil‐paper insulation system can significantly reduce its life expectancy, and for oil impregnated paper condenser type bushings, it is the most common cause of failure. Distinction between moisture contents using traditional power frequency tests of dissipation factor and capacitance can be difficult, particularly at ambient temperatures. Dielectric frequency response is becoming an established technique to measure the dissipation factor and capacitance of a bushing, but to date an accurate model to evaluate the condenser moisture content has not been presented using this technique. In this study, a dielectric frequency response bushing model is proposed and finite element method software is used to simulate the variation in dissipation factor and capacitance of a bushing with varying moisture content, as a function of frequency and temperature. The modelled results are compared with measurements reported in the literature and from the authors' own field measurements, where a good agreement is demonstrated. It is shown that the distinction in dissipation factor between moisture contents at frequencies <0.1 Hz is in excess of ten times greater than at 50 Hz. The proposed model can be used by practitioners to evaluate moisture content within the condenser insulation and distinguish between moisture contents ranging from 0.2 to 4.0%. [ABSTRACT FROM AUTHOR]