Conductivity Of Insulation Materials Research Articles

Dielectric Properties of Polymer Films in Strong Electromagnetic Field for Energy Storage Capacitor

In this article, polypropylene (PP), polyimide (PI), polyvinylidene difluoride (PVDF), and polyethylene (PE) dielectric materials are applied to analyze the performance degradation mechanism under magnetic field. The properties of the dielectrics are investigated under different magnetic fields. With the increase of magnetic field, the dielectric constant of materials is reduced and that of PVDF decreases the most. The conductivity of dielectric materials is all on the rise due to the magnetic field. Compared with under normal environment, the conductivity of the PVDF under 12-T magnetic field climbs to 574%, which is the largest increase in all dielectrics. The breakdown strength of PP and PE decreases by 17.2% and that of PVDF decreases by 22%. On the one hand, the magnetic field deflects the electric dipole in the opposite direction through Lorentz force, so as to limit the dipole steering and reduce the dielectric constant. On the other hand, the magnetic field increases the quantity of carriers by exciting electrons, which is the main reason for the decrease of breakdown strength. This article is of significance to the application of dielectric capacitors under harsh magnetic environment.

A special role of water in dielectrics of different structural organization

The paper presents some general patterns of the temperature behavior of thermodepolarization currents, dielectric permittivity and conductivity of dielectric materials containing water molecules or hydrogen bonds – crystallohydrates, polyelectrolytes, and biopolymers. The results indicate that the anomalies of these properties are observed at 4, 20, 35, 46, 65–76°С, which are “threshold points” of water, when its structure changes abruptly. The observed anomalies are probably due to a change in the proton energy at a transition to an excited level in the double-well potential at heating, while the equilibrium of the system is achieved by slow stepwise heating.

The Impact of Variable Thermal Conductivity of Insulation Materials on the Building Energy Performance in Hot Climate

This paper illustrates the impact of embedding an insulation layer of variable thermal conductivity in a typical building wall on the cooling effect and energy performance. The evaluation was performed by applying a conjugate heat transfer model, which was tested in extremely hot conditions of Al Ain (UAE). The thermal performance of a building incorporating insulation layers of variable thermal conductivity (k-value) was compared to a non-variable thermal conductivity system by quantifying the additional heat transferred due to the k-relationship with time. The results show that, when the k-value is a function of operating temperature, its effects on the temperature profile through the wall assembly during daytime is significant compared with that obtained when a constant k-value for the polystyrene (EPS) insulation is adopted. A similar trend in the evolution of temperatures during the day and across the wall section was observed when EPS material with different moisture content was evaluated. For the polyurethane insulation, the inner surface temperature reached 44 °C when constant k-value was adopted, increasing to 48.5 °C when the k-value was allowed to vary under the same ambient conditions.

Simulation of electric field distribution in the XLPE insulation of a 320 kV DC cable under steady and time-varying states

For HVDC cables, the electric field distribution is determined by the conductivity of insulation material, which is a function of temperature and field. As the result, the conductivity-dependent field in the DC insulation is an electro-thermal coupled field. A modified 2D model is set up in this paper to simulate the thermal field distribution of a 320 kV DC cable, and based on that, the electric field distribution in the XLPE insulation is studied by the finite element method without consideration of space charge effect. Electric field distribution of steady state is computed under thermal equilibrium and rated DC voltage, and it is found to be a quasi-linear function of the radius, with the field strength remaining nearly unchanged in the central part of the insulation, whose value is approximately equal to the average field. The field reversal is determined by the thermal activation energy in XLPE conductivity expression, with a larger activation energy corresponding to a lower temperature difference across the insulation when the field reversal happens, and the increase of electric field coefficient is beneficial for improving the field distribution. Simulation of the time-varying states is performed under thermal equilibrium and three typical transient waveforms, including the continuous rising DC voltage, polarity reversal DC voltage and the DC superimposed switching impulse. It is shown that the rise speed of the continuous rising voltage is a key parameter for the maximum field strength, with a high speed leading to a high field at the inner border of insulation, and a time duration of 2r to 3r is recommended for the voltage rise edge. By the consideration of the transition relaxation progress from the initial capacitive field to the steady-state resistive field, a formula is set up to calculate the field strength of the insulation after the application of a time-varying voltage, and the calculated results are highly consistent with those obtained by numerical simulation.

The combined effect of heat and moisture transfer dependent thermal conductivity of polystyrene insulation material: Impact on building energy performance

The aim of this article is to elucidate the combined impact of heat and humidity transfer on the thermal conductivity of polystyrene used as an insulation for building envelope. In building energy assessment, the conductivity of the insulation material is assumed to be constant. This yields inaccurate results, as the thermal conductivity, k-value, of any material is a complex function of many factors, such as temperature, moisture, and density. This dependence has been shown in extant studies and linear variation of the thermal conductivity vs. temperature have been proposed for fibrous materials. Accurate evaluation of building thermal comfort and energy assessment, which requires a precise calculation of the cooling load, and thus the sizing of the HVAC equipment, depends on the accurate determination of the thermal resistance of the building envelope components, the insulation material in particular. The aim of this work is thus to inspect the combined effect of operating temperature and moisture content on the thermal conductivity of polystyrene insulation material and its impact on the energy performance of buildings. The results reveal that the k-value of the polystyrene insulation is significantly influenced by its moisture content at different operating temperatures. Indeed, an 8% increase in the total cooling load calculated at 28 °C and 30% moisture was measured relative to the base case evaluated at 24 °C and 0% moisture.

Numerical modelling of processes that occur in the selective waste disassembly installation

This paper is the result of the attempts of quantitative approach of some of the processes that are occurring in the selective fragmentation with high voltage pulses installation. It has been formulated a methodology which customizes the general methods for the issue of transient electric field in mixed environments. The electromagnetic processes inside the fragmentation installation, the initiation and formation of the discharge channels, the thermodynamic and mechanical effects in the process vessel are complex, transient and very quick. One of the underlying principles of the fragmentation process consists in the differentiated reaction of materials in an electric field. Generally in the process vessel there can be found together three types of materials: dielectrics, metal, electrolytes. The conductivity of dielectric materials is virtually zero. Metallic materials conduct very well through electronic conductivity. Electrolytes have a more modest conductivity since they conduct through electrochemical processes. The electrical current, in this case, is the movement of ions having sizes and the masses different from the electrons. Here, the electric current includes displacements of ions and molecules, collisions and chemical reactions. Part of the electrical field’s energy is absorbed by the electrolyte in the form of mechanical and chemical energy.

Advances in heat conduction models and approaches for the prediction of lattice thermal conductivity of dielectric materials

An overview of predominant theoretical models used for predicting the thermal conductivities of dielectric materials is given. The criteria used for different theoretical models are explained. This overview highlights a unified theory based on temperature-dependent thermal-conductivity theories, and a drifting of the equilibrium phonon distribution function due to normal three-phonon scattering processes causes transfer of phonon momentum to (a) the same phonon modes (KK-S model) and (b) across the phonon modes (KK-H model). Estimates of the lattice thermal conductivities of LiF and Mg2Sn for the KK-H model are presented graphically.

Insulation Design of a Stop Joint Box of 80-kV DC HTS Cables Based on DC Electric Field Analysis

Among the accessories of the dc high-temperature superconducting (HTS) power cable, a stop joint box (SJB) is an essential component for the long-distance transmission cable connections and the separation of the cooling section. The main insulating material of the SJB is a polypropylene laminated paper (PPLP), which is already generally used for dc HTS power cable. In order to separate the cooling section, an epoxy spacer is located at the center of the SJB. Due to the weakness of surface breakdown characteristics compared with that of punctual breakdown and different nature of dc electric field distribution determined by the ratio of conductivities of dielectric materials, the epoxy spacer configuration of the SJB should be carefully designed based on dc electric field analysis. In this paper, the optimum configuration of the epoxy spacer of the SJB was investigated based on dc electric field analysis. On the basis of the initial SJB model, which is already designed for the joint box of the conventional ac oil-filled power cable, a variety of improved SJB models with different epoxy spacer configurations were considered. In dc electric field simulations, the main objective was to reduce the tangential dc electric field intensity at the interface between PPLP and epoxy spacer. To find the optimum epoxy spacer configuration, a parametric sweep technique was applied, and an appropriate SJB model could be identified. However, its tangential dc electric field intensity remained still higher than that of the design criteria for the dc electric field from the experimental results. Therefore, as a novel method, a thin Kraft layer between the PPLP and the epoxy spacer was added to reduce electric field intensification. The simulation result of the newly designed insulation structure revealed the possibility of lowering the tangential electric field. Furthermore, different electrical conductivity values were applied to the additional layer instead of the original Kraft value in order to meet the critical electric field intensity. Finally, 1E-11 S/m, among those values, showed the best simulation result, which was lower than the design criteria for the dc electric field. To verify the effect of the additional layer for dc electric field mitigation, miniature SJB specimens were fabricated, and dc breakdown tests were performed using a step-by-step test method. Based on the experimental results, SJB specimens with an additional layer showed the highest breakdown strength compared with that of SJB specimens without an additional layer. Thus, the optimum configuration of SJB determined by dc electric field analysis was approved by experimental works. Consequently, these insulation design skills based on dc electric field analysis could be usefully adopted in developing the SJB of 80-kV dc HTS power cables.

Analyze the Effect of Thermal Conductivity of Cold Insulation Materials in Cryogenic Engineering

The pipe heat transfer models were constructed, respectively, to simulate the cryogenic insulated structure, nonlinear partial differential equations was obtained considering the temperature-dependent variation in thermal conductivity of insulation materials. In order to get the temperature profile of insulation layer, Kirchhoff integral method was introduced to process, program, and iteratively calculate the simplified energy equations. The influence of heat-transfer process related to the thermal conductivities of four cold insulators was analyzed. Results indicate that phenolic foam, hydrophobic perlite, and RPUR have superior low-temperature insulation at cryogenic environment, while foam glass has better low-temperature insulation at normal temperature. The thickness of inner cryogenic-insulation layer can be reduced largely by using a multicomponent cold insulator in the discharge pipe of LNG stations, which can save both materials and costs. Meanwhile, it offers a new method to solve variable thermal conductivities.

STUDY OF THE CONDUCTIVITY OF DIELECTRIC UNDER HIGH ENERGY ELECTRON IRRADIATION

High energy electron irradiation was performed on a theoretical and experimental study of the dielectric conductivity. This paper presents a theoretical method to the determination of the conductivity of dielectric materials under irradiation, and the conductivity of kapton is measured under 0.8 MeV electron irradiation. The results from theory and experiment clearly illustrate the expected dependence of conductivity of dielectric on dose rate, and the resistance of kapton decreases in 102.

Electric Relaxational Effects Induced by Ionic Conductivity in Dielectric Materials

The paper shows how the direct current ionic conductivity (σDC) and the static dielectric permittivity (εs) reveal themselves in the complex impedance, the electric modulus, and the conductance of molecular liquids when the frequency of the electric stimulus is much lower than that corresponding to the dipolar reorientational relaxation of the liquid under investigation. It was shown that, in such static dielectric conditions, one observes the relaxational behavior of the impedance and the electric modulus, both of the Debye-type and of the same relaxation time, depending on σDC and εs values. The discussion is illustrated with the experimental electric spectra of liquid cyclobutanone recorded in the frequency region from 500 Hz to 5 MHz and in the temperature range from 243 to 313 K.

Lattice thermal conductivity of skutterudite compounds

A generalized expression is used on the basis of relaxation time approximation to facilitate calculation of lattice thermal conductivity of dielectric materials as well as skutterudite family consists of compounds of the form AB3. It is assumed that phonon scattering processes are independent and is represented by frequency dependent relaxation times. The contributions of normal three phonon scattering processes are included explicitly as redistribution of phonon momentum between two oscillation branches is considered. Magnitudes of relaxation times are estimated from the experimental data. The result for CoSb3 is in reasonably good agreement with the experimental result in the temperature range 1–1000°K. It is observed that redistribution of phonon momentum between two oscillation branches leads to a significant suppression of thermal conductivity maximum and it is observed that for unfilled skutterudite the main dominant mechanism at the thermal conductivity maximum is three phonon normal scattering process.

A compact interconnect temperature distribution model considering the via effect and the heat fringing effect

Considering the via effect and the heat fringing effect simultaneously，we proposed a compact interconnect temperature distribution model that can be applied for single interconnect and multilevel interconnects. Based on the 65 nm complementary metal-oxide semiconcluctor （CMOS） interconnect and material parameter，the temperature distribution of multilevel interconnects and single interconnect with different lengths was calculated. The results show that the temperature rise of global interconnect is still large when the via effect is considered，while the temperature rise of intermediate line and local line is quite small. For multilevel interconnects，the temperature rise in the uppermost layer interconnect is the largest. The temperature rise is approximately proportional to the thickness of insulator，and will rise higher if the thermal conductivity of dielectric materials becomes smaller. The proposed interconnect temperature distribution model can be used in nanometer CMOS computer-aided design.

Effect of Spatially Varying Thermal Conductivity on the Magnitude of Thermal Stress in Brittle Ceramics Subjected to Convective Heating

The effect of a spatial variation of the thermal conductivity on the magnitude of the maximum tensile thermal stress in a solid circular cylinder subjected to sudden convective heating was calculated by finite element methods. The general results show that by lowering the thermal conductivity in the surface region of the cylinder, the magnitude of the maximum tensile thermal stress at the center of the cylinder is reduced significantly. The negative temperature dependence of the thermal conductivity in dielectric materials, which indirectly creates a spatial variation in thermal conductivity, also causes a significant decrease in the magnitude of the tensile thermal stresses, as demonstrated by a numerical example for aluminum oxide. It is also shown that a spatial variation in thermal conductivity can significantly affect the time to maximum tensile stress as well.

Evaluation of dielectric permittivity and conductivity by time domain spectroscopy. Mathematical analysis of Fellner-Feldegg's thin cell method

A mathematical analysis is presented of Fellner-Feldegg's thin cell method from which the permittivity and conductivity of dielectric materials can be obtained in the time domain. It is proved that the thin cell response has to be interpreted as a Taylor expansion of the step response around l=0. The first term in the expansion (Fellner-Feldegg's thin cell relation) can be found by integration over the ordinary Laplace contour (c − i ∞, c + i ∞). The other coefficients can be obtained from complex integration over a contour W enclosing all singularities of the integrand. Restrictions on the thickness of the sample are derived from the requirement that the second term in the expansion must be small relative to the first one. The step response is also calculated with asymptotic methods and with numerical methods for three currently used permittivity relations. Also, conductivity is included. For Debye materials a relation is found that tends to give a better fit to the exact response than the thin cell relation. For such materials the relaxation time found experimentally, using the thin cell relation, is always too large. An iteration procedure is suggested to obtain the correct relaxation time. For conductive materials the thin cell approximation leads to an incorrect value of the offset of the base line. The correct relation is derived.

Measurement of Attenuation Constant and Conductivity of Dielectric Materials with Cylindrical Radiator at Microwave Frequency

Measurement of Attenuation Constant and Conductivity of Dielectric Materials with Cylindrical Radiator at Microwave Frequency

Conductivity-Temperature Curves of Paraffin Wax

IT is usually supposed that the conductivity of dielectric materials increases continuously with increase in temperature. The only recorded exception to this normal behaviour appears to be by Gemant1, who found that the D.C. conductivity of a heavy cable oil decreased temporarily from –40° to –20° C. I have recently observed a similar peculiar phenomenon, together with a hysteresis effect, in D.C.conductivity measurements over the temperature range from 0° to 50° C. on a sample of paraffin wax (melting between 45° and 55° C.). The results of a cycle of measurements under a continuously applied voltage gradient of 500 volts per cm. are shown in Fig. 1. Commencing at the point A, the temperature was lowered to B, then raised at a rate of about 1° C. in 5 minutes along the curve BCD, and finally decreased at the same rate along DEB´. On regaining room temperature very slowly from B´, the conductivity had risen to F, and with temperature rise from this point followed the curve FGD. On subsequent slow cooling to room temperature, the conductivity attained the value H.