Cylindrical Insulator Research Articles

Insulation Resistance Degradation Models of Extruded Power Cables under Thermal Ageing

Insulation resistance (IR) is an essential metric indicating insulation conditions of extruded power cables. To deliver reliable IR simulation as a reference for practical cable inspection, in this paper, four IR degradation models for cross-linked polyethylene-insulated cables under thermal ageing are presented. In addition, the influences of methodologies and temperature profiles on IR simulation are evaluated. Cable cylindrical insulation is first divided into sufficiently small segments whose temperatures are simulated by jointly using a finite volume method and an artificial neural network to model the thermal ageing experiment conditions. The thermal degradation of IR is then simulated by dichotomy models that randomly sample fully degraded segments based on an overall insulation (layer) ageing condition estimation and discretization models that estimate the gradual degradation of individual segments, respectively. Furthermore, uniform and non-uniform temperature profiles are incorporated into dichotomy and discretization models, respectively, for a comparison. The IR simulation results are not only compared between different models, but also discussed around the sensitivity of IR simulation to segment sizes and degradation rates. This provides cable assessment engineers with insights into model behaviour as a reference for their selection of appropriate IR degradation models.

Analytical Solution of Transient Heat Conduction through a Hollow Cylindrical Thermal Insulation Material of a Temperature Dependant Thermal Conductivity

The one-dimensional, cylindrical coordinate, non-linear partial differential equation of transient heat conduction through a hollow cylindrical thermal insulation material of a thermal conductivity temperature dependent property proposed by an available empirical function is solved analytically using Kirchhoff’s transformation. It is assumed that this insulating material is initially at a uniform temperature. Then, it is suddenly subjected at its inner radius with a step change in temperature. Four thermal insulation materials were selected. An identical analytical solution was achieved when comparing the results of temperature distribution with available analytical solution for the same four case studies that assume a constant thermal conductivity. It is found that the characteristics of the thermal insulation material and the pressure value between its particles have a major effect on the rate of heat transfer and temperature profile.

Two modes of vacuum flashover process under pulsed voltage

Vacuum flashover process can be influenced by various factors, such as gap length, applied voltage form, electric and magnetic field structures, and so on, leading to different flashover voltages and flashover times under a pulsed voltage. Particle-in-cell (PIC) simulation results in this paper show two typical vacuum flashover modes: (a) the area of high space charge density appears after electrons run across the gap and extends from the anode to cathode and (b) the area of high space charge density appears before electrons run across the gap and extends from the middle to both ends of the gap. In order to verify the PIC simulation results, a probe that measures the change in the electric field between the gap is embedded in the anode, the experimental waveform of which shows different features when the shape of insulator is different. Simulation results and experimental waveforms indicate that the flashover process of certain cylindrical insulators corresponds to the first mode, while the flashover process of certain conical insulators with an acute angle between the cathode and dielectric corresponds to the second mode.

Determination of Breakdown Voltage Along the Surface of a Cylindrical Insulator

This article investigates the electric breakdown along the surface of a cylindrical dielectric, part of a coaxial transmission line. The particular geometry of the insulator is very common, as it is used at the input or output of most high-power, high-voltage (HV) generators. The streamer propagation criterion is used to calculate the flashover voltage. Studies of the dependence of the flashover voltage on the distance between the electrodes obtained in tests with dc voltage and also by applying voltage impulses with different durations and rise times are reported. The highest difference between the estimated values and the experimental data is less than 15%, which proves the applicability of the criterion for determining the surface breakdown voltage within the geometry under study. In particular, the results of these studies are used in the design of a compact 0.5-MV pulsed power system currently under development.

Structural Analysis and Optimization of Steel Pin on Cylindrical Head Suspension Porcelain Insulators

There is no essential difference in theory between the inner and outer insulating properties of cylindrical and conical head disc suspension porcelain insulators. Compared with a conical head porcelain insulator, a cylindrical head porcelain insulator is significantly lighter in weight, which can effectively reduce the mechanical load of the tower and wire; and it has better dispersion and adjustment capabilities for changes in material properties over time, so that the product is not subject to excessive and uneven stress over a long-term. In order to improve the mechanical performance of cylindrical head insulator products, this paper establishes a parameterized fine simulation model of the steel pin without changing the geometry of the insulator iron cap and porcelain body. The finite element method is used to calculate and analyze how the geometric parameters of the steel pin influence insulator mechanical properties, which can provide design reference for further product optimization.

Research and development of discharge free insula-tion of wires for space application

The present research aimed to investigate a charging of the cylindrical insulation layer of wires for space applications under the influence of isotropic electron radiation with an electron injection uniform in the volume of the dielectric. An analytical solution of the first-order differential equation resulting from the proposed charging model is obtained. A software has been developed and received state registration that allows for a complete calculation of the physical parameters of space-application wires resistant to electrification effects. The obtained results are proposed to be used for modeling and testing of wires for space applications in order to completely exclude the physical possibility of the occurrence of electrostatic discharges (ESR) of the "insulation-core" type during the operation (of the spacecraft) in orbit during geomagnetic disturbances in the Earth's magnetosphere. Keywords: electricity, bulk charging, insulation, dark conductivity, electrostatic discharge.

Исследование и разработка безразрядной изоляции проводов космического применения

The present research aimed to investigate a charging of the cylindrical insulation layer of wires for space applications under the influence of isotropic electron radiation with an electron injection uniform in the volume of the dielectric. An analytical solution of the first-order differential equation resulting from the proposed charging model is obtained. A software has been developed and received state registration that allows for a complete calculation of the physical parameters of space-application wires resistant to electrification effects. The obtained results are proposed to be used for modeling and testing of wires for space applications in order to completely exclude the physical possibility of the occurrence of electrostatic discharges (ESR) of the "insulation-core" type during the operation (of the spacecraft) in orbit during geomagnetic disturbances in the Earth's magnetosphere.

Surface Charge Inversion Method on Cylindrical Insulators Based on Surface Potentials Measured Online

In this paper, a model of the Kelvin probe is established in COMSOL Multiphysics based on electrostatic field theory, and it is verified by measuring the surface potentials. The influence of the probe is also investigated. An improved charge inversion method based on surface potentials measured online is proposed. The surface charge density is directly obtained by the Gauss's theorem to avoid the calculation of the inversion matrix. The improved method is verified by comparing the surface charge density calculated by the analytical method. When considering the effect of the probe, the maximum difference in surface charge density is 0.3 μC/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> comparing to that when ignoring its effect, and the percentage of the difference is as high as 41%. The results indicate that the effects of the voltage of the probe under online measurement conditions must be considered.

Finite-size effects in cylindrical topological insulators

We present a theoretical study of a nanowire made of a three-dimensional topological insulator. The bulk topological insulator is described by a continuum-model Hamiltonian, and the cylindrical-nanowire geometry is modelled by a hard-wall boundary condition. We provide the secular equation for the eigenergies of the systems (both for bulk and surface states) and the analytical form of the energy eigenfunctions. We describe how the surface states of the cylinder are modified by finite-size effects. In particular, we provide a 1/R expansion for the energy of the surface states up to second order. The knowledge of the analytical form for the wavefunctions enables the computation of matrix elements of any single-particle operators. In particular, we compute the matrix elements of the optical dipole operator, which describe optical absorption and emission, treating intra- and inter-band transition on the same footing. Selection rules for optical transitions require conservation of linear momentum parallel to the nanowire axis, and a change of 0 or ±1 in the total-angular-momentum projection parallel to the nanowire axis. The magnitude of the optical-transition matrix elements is strongly affected by the finite radius of the nanowire.

Construction of microgrooves on the surface of alumina ceramic insulator to enhance its flashover strength

The fabrication method of grooves on the surface of alumina and their influence on the surface flashover characteristics of the alumina insulator were studied in this paper. To prepare grooves with a regular surface structure, the UV laser was applied to carve grooves on the surface of alumina ceramic, and dilute hydrochloric acid was used to corrode and remove the residual materials produced in the laser carving process. By adjusting the laser parameters, periodic grooves were prepared on the surface of a cylindrical alumina insulator with a groove depth of 60 µm and a groove width of approximately 50 µm on the laser spinning carving platform. Then, alumina insulators with different periods were prepared, and their vacuum surface flashover voltages were tested on a short pulsed high-voltage test platform. The test results indicated that the flashover voltages of the alumina insulators with laser carved periodic grooves were increased over 200%, and the improvement did not change much with the groove periods. A further study of the groove parameters showed that several grooves fabricated on the cathode end of the insulators were able to improve the flashover voltage of the alumina insulator to the voltage-withstand level of the fully grooved insulators.

Magnetoconductance, Quantum Hall Effect, and Coulomb Blockade in Topological Insulator Nanocones.

Magnetotransport through cylindrical topological insulator (TI) nanowires is governed by the interplay between quantum confinement and geometric (Aharonov-Bohm and Berry) phases. Here, we argue that the much broader class of TI nanowires with varying radius-for which a homogeneous coaxial magnetic field induces a varying Aharonov-Bohm flux that gives rise to a nontrivial masslike potential along the wire-is accessible by studying its simplest member, a TI nanocone. Such nanocones allow us to observe intriguing mesoscopic transport phenomena: While the conductance in a perpendicular magnetic field is quantized due to higher-order topological hinge states, it shows resonant transmission through Dirac Landau levels in a coaxial magnetic field. Furthermore, it may act as a quantum magnetic bottle, confining surface Dirac electrons and leading to a largely interaction-dominated regime of Coulomb blockade type. We show numerically that the above-mentioned effects occur for experimentally accessible values of system size and magnetic field, suggesting that TI nanocone junctions may serve as building blocks for Dirac electron optics setups.

Surface Discharges and Flashover Modelling of Solid Insulators in Gases

The aim of this paper is the presentation of an analytical model of insulator flashover and its application for air at atmospheric pressure and pressurized SF6 (Sulfur Hexafluoride). After a review of the main existing models in air and compressed gases, a relationship of flashover voltage based on an electrical equivalent circuit and the thermal properties of the discharge is developed. The model includes the discharge resistance, the insulator impedance and the gas interface impedance. The application of this model to a cylindrical resin-epoxy insulator in air medium and SF6 gas with different pressures gives results close to the experimental measurements.

Phase diagram and phonon-induced backscattering in topological insulator nanowires

We present an effective low-energy theory of electron-phonon coupling effects for clean cylindrical topological insulator nanowires. Acoustic phonons are modelled by isotropic elastic continuum theory with stress-free boundary conditions. We take into account the deformation potential coupling between phonons and helical surface Dirac fermions, and also include electron-electron interactions within the bosonization approach. For half-integer values of the magnetic flux $\Phi_B$ along the wire, the low-energy theory admits an exact solution since a topological protection mechanism then rules out phonon-induced $2k_F$-backscattering processes. We determine the zero-temperature phase diagram and identify a regime dominated by superconducting pairing of surface states. As example, we consider the phase diagram of HgTe nanowires. We also determine the phonon-induced electrical resistivity, where we find a quadratic dependence on the flux deviation $\delta\Phi_B$ from the nearest half-integer value.

Volume and surface memory effects on evolution of streamer dynamics along gas/solid interface in high-pressure nitrogen under long-term repetitive nanosecond pulses

Evolution of the surface streamer and the discharge mode transition from the corona discharge to the surface flashover were investigated by pulse sequence resolved electrical and optical measurements under long-term repetitive nanosecond pulses (RNP). The test sample was a cylindrical epoxy resin insulator attached with a needle electrode in 0.1–0.4 MPa nitrogen. Under positive RNP, the inception phase of subsequent streamer discharges decreases with increasing the pulse repetition frequency (PRF), and a periodical streamer stagnation phenomenon appears at high gas pressure. Under negative RNP, the surface streamer does not illustrate symbolic decreasing tendencies in light intensity and corona inception phase in gas gap. The dependence of the evolution of surface streamer velocity on PRF is correlated with the repulsive force from surface charges and the accessibility of seed electrons. Statistical characteristics of back discharges under negative RNP are qualitatively explained by the local electric field around the triple junction. The reversal phenomenon of polarity effect of the allowable repetitive working coefficient is probably resulted from the corona stabilization effect, the surface electron detrapping process, and the assistance of background electric field. Principal results qualitatively support that behaviors of surface streamer and flashover are dominated by the electric field distribution, volume and surface memory effects as well as their interactions and bidirectional transformations, which are different from the monotonically facilitative tendency predicted by the metastable-species-dominated memory effect mechanism.

Heat transfer through combined thermal insulation of cylindrical vacuum resistive furnace

The paper is devoted to simulation problem of heat transfer in vacuum shaft electric resistive furnace with combined insulation. Concept of critical diameter of cylindrical combined thermal insulation is explained. Physical-and-mathematical model for investigation of interconnection of geometrical and thermophysical parameters of the combined thermal insulation with heat flow through it is proposed. Dependences of effective heat transfer coefficient of screen partition of the combined thermal insulation and effective critical diameter of the insulation partition of the combined insulation upon its geometrical and thermophysical parameters are uncovered.

Magnetoelectric effect in cylindrical topological insulators

Topological insulators (TIs) exhibit a quantized magnetoelectric response when time-reversal symmetry is broken on its surface. This unusual electromagnetic (EM) response is a unique macroscopic manifestation of the quantum Hall effect on the TI surface and it is described by a quantized Chern-Simons theory. In this paper, we construct the Green's function (GF) describing the EM response of two topological media separated by a cylindrical interface. This GF, in the appropriate limits, describes the magnetoelectric effect of both i) a cylindrical TI surrounded by a dielectric fluid, and ii) a TI with a cylindrical dielectric-filled cavity. We calculate the EM fields produced by a line charge and a line current near the TI surface and we show that, in addition to the standard image electromagnetic sources, charge and current densities of magnetic monopoles will also appear. We discuss some experimental setups which could be used to test these magnetic monopole fields.

A rotating rod electrode disk as an alternative to the rotating disk electrode for medium-temperature electrolytes, Part I: The effect of the absence of cylindrical insulation

In this paper, a rotating rod electrode disk is introduced as a hydrodynamic electrode and both the electrolyte flow hydrodynamics as well as mass transport towards the disk were investigated and compared with the rotating disk electrode. The main difference to the rotating disk is the absence of disk insulation leading to slightly enhanced mass transport towards the disk surface. Based on a combination of experiments and mathematical modelling for a broad range of kinematic viscosity values of the electrolyte solution, a correction of the Levich equation was introduced. This enables recalculation of the data determined using the rotating rod disk electrode so that they are equivalent to those of the rotating disk electrode. Although glassy carbon was used as the material of the rotating rod electrode in this work, in principle any other suitable material can be used. Thus, it can be concluded that the rotating rod electrode disk represents a cheap and effective tool easily applicable for measurements with controlled electrolyte convection in systems that are hardly manageable using a conventionally constructed rotating disk electrode. Good examples are melts or electrolyte solutions at temperatures above 80 °C. The applicability of the rotating rod electrode disk was successfully tested in the continuation (Part II) of this study. There, the thin-film modified (activated) rotating rod electrode disk was used for determining the mass transport properties of the oxygen and kinetic constants of the oxygen reduction reaction in concentrated phosphoric acid at 160 °C.

Flashover characteristics of cylindrical insulator in high-speed sand environment

With the launching of Lanzhou-Xinjiang high-speed railway in Northwest China, high-speed train running in sand environment will cause strong high-speed airflow with sand around it, which seriously threats the long-term service performance of roof insulators. To study the flashover characteristics of insulator under the condition, a small size wind tunnel system is established to simulate high-speed sand environment, the influence of airflow speed, sand particle size and sand flux on the flashover voltage of cylindrical insulator is investigated. Results show that, in pure high-speed airflow environment, the flashover voltage of insulator has an increase-decrease variation trend with the increase of airflow speed. The flashover mechanism is due to the combined effects of airflow blowing effect and airflow density. In sand environment, flashover voltage will decrease obviously which is caused by nonuniformity of electric field, but the decreasing degree will become small with the increase of airflow speed. Sand particle size and sand flux have negative influence on flashover voltage of insulator. These research results can provide theoretical basis for service performance of roof insulators in high-speed sand environment.

Alumina ceramic based high-temperature performance of wireless passive pressure sensor

A wireless passive pressure sensor equivalent to inductive-capacitive (LC) resonance circuit and based on alumina ceramic is fabricated by using high temperature sintering ceramic and post-fire metallization processes. Cylindrical copper spiral reader antenna and insulation layer are designed to realize the wireless measurement for the sensor in high temperature environment. The high temperature performance of the sensor is analyzed and discussed by studying the phase-frequency and amplitude-frequency characteristics of reader antenna. The average frequency change of sensor is 0.68 kHz/°C when the temperature changes from 27°C to 700°C and the relative change of twice measurements is 2.12%, with high characteristic of repeatability. The study of temperature-drift characteristic of pressure sensor in high temperature environment lays a good basis for the temperature compensation methods and insures the pressure signal readout accurately.

Detection of partial discharges occurring on HV cylindrical insulator made of porcelain using the spectrophotometry method

Detection of partial discharges occurring on HV cylindrical insulator made of porcelain using the spectrophotometry method