Dielectric Tests Research Articles

High heat‐resistant (250°C) epoxy resin composites with excellent dielectric properties

AbstractInsulated gate bipolar transistor (IGBT) is the core of electric energy conversion and circuit control, which is widely used in the field of electric vehicles. Higher service temperature, higher power density, and higher operating voltage are the tendency for IGBT in which packing materials have to possess more stable temperature resistance and better insulating properties. In this work, cyanate ester (CE) and polyhedral oligomeric silsesquioxanes (POSS) are introduced into epoxy with various filling ratio to improve the dielectric and thermal properties. The curing process of every system is determined by non‐isothermal differential scanning calorimetry (DSC). N and Si element distribution mappings indicate that there are good compatibility between POSS, CE, and epoxy. The dielectric test shows that the dielectric constant decreases from 4.34 to 2.84 at 1 MHz and from 4.76 to 2.93 at 1 kHz when the filling ratio is 60 wt%. Meanwhile, the DC breakdown strength increases from 172.7 to 286.4 kV/mm. Furthermore, the glass transition temperature (Tg) increases from 180 to 263°C and the yield of residual carbon increases from 6.2% to 23.7%. A new packing material, which can endure 250°C of operating temperature and has excellent dielectric properties has been synthesized.

Fault diagnosis technologies for power transformers during the on‐site inductive oscillating switching impulse voltage withstand test

Although oscillating switching impulse (OSI) voltage is recommended for the transformer field test, the lack of corresponding fault diagnosis technologies limits its application in the field. In this study, the inductive OSI test technology and diagnostic methods are investigated. The front time and the oscillation frequency of the OSI are altered by changing the additional inductance, whereas the tail time is affected by both the front and tail resistance. The OSI voltage withstand test is carried out on a 110 kV three-phase double-winding transformer on site. Furthermore, transfer function (TF) analysis is used for the diagnosis of transformer insulation with high sensitivity during the OSI test. The fault winding is distinguished by comparing the change in the voltage TF and current TF at different voltage levels. The partial discharge (PD) detection method has the highest sensitivity, which realizes the early diagnosis of insulation faults. The insulation status of the windings is ascertained based on the number and amplitude of PDs. The test results prove that the inductive OSI voltage withstand test is easy to perform on site and can successfully diagnose the insulation faults of the transformer in more detail compared with other routine insulation tests.

A High-Efficiency 80-kW Split Planar Transformer for Medium-Voltage Modular Power Conversion

A high-efficiency medium-frequency split planar transformer (MFSPT) based on low-cost ferrite core (PC40) is proposed for medium-voltage modular power conversion. By adopting a split planar structure, high electrical insulation is achieved with high efficiency, high power density, as well as excellent heat dissipation performance at the same time. A finite-element analysis simulation is carried out to investigate the distribution of the magnetic field and electric field in the MFSPT. The designed MFSPT prototype achieves a power density of 21.1 kW/L and electrical insulation of 42 kV. The performance of the proposed MFSPT is experimentally evaluated on an 80 kW, 43 kHz <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> converter and the peak efficiency of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> converter is 99.33%. This letter shows for the first time that high power, high power density, high efficiency, and high electrical insulation can be achieved simultaneously by using the split planar structure. This letter is accompanied by a supplementary file demonstrating the applied voltage insulation test.

The synthesis and the effect of Cu on optoelectronic qualities of β-In2S3 as a window layer for CIGS thin film solar cells

In this paper, the vacuum thermal evaporation technique was used to investigate β-In2S3 doped with copper (Cu) as window layer thin film for solar cells. The amount of the Cu source was used to be 0–8 % atomic weight compared with In2S3 source. For various Cu doping levels, the characteristics of the thin films were studied utilizing structural, morphological, and optical characterization techniques, as well as dielectric testing. The research included X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDS), Infrared analysis (FTIR), XPS, Ellipsometry and UV-NIR spectroscopy. The measurements demonstrated that the real and imaginary isolation constants were over the wavelength range and successfully estimated the Urbach energy (Eu) and band gap energy. The Urbach energy varied from 1.88 to 2.21 eV. The band gap energy decreases from 2.10 to 1.93 eV for direct transitions. Moreover, based on the measured optical constants (n and k), employing the Wemple-Didomenico model helped uncover the Cauchy coefficients’, the refractive index, the dispersion and the oscillation energies. Therefore, the results presented in this paper show that the use of Cu-In2S3 for perovskite cells offers a high-efficiency alternative in the solar energy field.

The Influence of SiO2 + SiC + Al (H2PO4)3 Coating on Mechanical and Dielectric Properties for SiCf/MWCNTS/AlPO4 Composites.

SiC fiber-reinforced AlPO4 matrix (SiCf/MWCNTs/AlPO4) composites were fabricated using a hot laminating process with multi-walled carbon nanotubes (MWCNTs) as the absorber. A coating prepared from SiO2 + SiC + Al (H2PO4)3 was applied to the surface of the SiCf/MWCNTs/AlPO4 composites prior to an anti-oxidation test at 1273 K in air for 40 h. The anti-oxidation effect was verified by a three-point bending test, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and a dielectric property test. Anti-oxidation mechanism investigations revealed that the coating effectiveness could be attributed to three substances, i.e., SiO2, SiP2O7, and SiO2 + AlPO4 solid solution from the reactions of SiC + O2→SiO2 + CO, SiO2 + P2O5→SiP2O7 and SiO2 + AlPO4→solid solution, respectively.

Partial Discharge Behavior of Epoxy-Mica Insulation System under Superimposed AC and DC Voltage Stress

Recent technology advances in wind energy conversion systems include a new type of permanent magnet synchronous generator with a segmented stator that allows lightweight concepts with high efficiency and superior controllability. Each stator segment is driven by a separate power converter. The various cascaded power converters can be connected in series and in parallel, which ultimately leads to the superposition of a DC and an AC voltage stress in the insulation of the stator coils. The resulting DC-AC mixed voltage is an entirely new electrical stress for the epoxy-mica insulation system that is typically utilized as main insulation of rotating electrical machines. In order to resemble this stress, typical dielectric tests such as partial discharge (PD) measurements and long-term aging of model insulation systems have to be be carried out under DC-AC mixed voltage stress. The mentioned investigations are presented in this contribution. The results indicate that the AC voltage is dominant with regard to the PD inception and influences the PD parameters such as the apparent charge and the repetition rate substantially when compared to the DC voltage proportion. The accelerated aging tests with significantly higher AC-DC mixed voltage stress than is expectable under operating conditions revealed no measurable PD deterioration of the investigated insulation systems.

Physico-chemical Characterization of Paint Films with Electromagnetic Properties

Electromagnetic compatibility issues and those generated by these radiations are a major concern for electrical and electronic products, mainly in the fields of communications, information technology, transportation, security and medical services. The paper presents the way to obtain nanostructured paint/plastic/nanopowder paint systems with electromagnetic shielding properties, as well as their characterization by FTIR analysis, DSC and dielectric tests. These systems have Electro-magnetic Interference (EMI)/Electromagnetic Compatibility (EMC) and Electrostatic Discharge (ESD) applications in the manufacture of enclosures for various electronic devices and for the automotive industry. At the laboratory level, 4 non-additive experimental models (EM) coded M1-M4 and 16 additive experimental models coded M5-M20 were obtained. Revolutionary to these materials is the fact that inside they are insulating and, on the outside, they behave like a shield. The results obtained from the dielectric tests performed on the 16 additive systems showed that the samples with a maximum percentage (20 %) of metal nanopowders show the highest values of electrical conductivity. Of the two nanopowders used, that of Fe from samples M11, M12, M19 and M20 which induces the composite higher conductivities than Al nanopowders. The ATR/FTIR spectra of the two paint samples analyzed showed that they were almost identical, suggesting that the paints tested had the same basic chemical structure. DSC analysis showed that pigment paint (V2) has low thermal oxidation stability and lower decomposition temperatures than pigment-free paint (V1), therefore, V2 is less stable under usage conditions, under the influence of normal environmental factors (temperature, humidity, natural or artificial light, etc.) compared to V1.

Quadrature phase shifter for the measurement systems of testing of electrical insulation

Quadrature phase shifters are widely used in practice of development of measurement systems intended for the measurements of dielectric dissipation factor and electrical capacitance. This article presents the examples of implementation of phase shifters intended to obtain the value of phase shift equal to 90º for the applying in measurement systems of monitoring and diagnosing the technical condition of electrical insulation. The developed solutions are based on applying of the analog signal multiplier implemented in the AD633 integrated circuit. The required value of phase shift is provided by adding a pre-shifted at a certain angle input harmonic signal to a signal with the reduced amplitude and the opposite initial phase. The article is also focused on the development of schematic solutions which can be used in order to remove the undesirable for many practical applications discrepancy between the amplitudes of the input and the output signals. This alignment of amplitudes is provided by the detection of their average rectified values with subsequent multiplication of their ratio by the shifted at 90º signal with the reduced amplitude. The designed schematic solutions imply the applying of analog circuits which contain the input phase shifter, low pass filter, voltage summing amplifier, two detectors of average rectified values, three analog multipliers and one voltage divider.

A Study on the Influence of End-Sheath Aging and Moisture Absorption on Abnormal Heating of Composite Insulators

Abnormal heating of composite insulators of high-voltage transmission lines concentrate at its end, especially in a high-humidity environment. In order to study the influence of end-sheath aging and moisture absorption on abnormal heating of composite insulators, in this paper, we first discuss the appearance test, temperature rise test, and dielectric characteristic test conducted on 110 kV decommissioned composite insulators. Test results indicated the temperature rise in composite insulators increased with ambient humidity, but temperature rise was not severely affected by surface contamination of its shed and sheath; in dry environments, the dielectric constant and dielectric loss factor of high-voltage end sheaths are higher than of those of medium- and low-voltage end sheaths, and the loss effect becomes more severe after moisture absorption in a high-humidity environment. After the tests, the authors established a COMSOL simulation model of composite insulators, to analyze changes in the electric field and thermal field of the end sheath of composite insulators due to the coupling of electric and thermal fields. It was concluded that the dielectric constant of a high-voltage end sheath of the composite insulator increased after moisture absorption, distorting the partial electric field on the surface; meanwhile, the dielectric loss factor increased significantly after water molecules intruded into the aging layer of the sheath as polar molecules. Therefore, the dielectric loss (leakage conductance loss and lossy polarization loss) caused by aging and moisture absorption of the sheath surface under partially high field strength in the high-humidity environment was the leading cause of abnormal heating at the high-voltage end of composite insulators. The conclusion of this paper serves as an important reference for revealing the causes of abnormal heating of composite insulators in high-humidity environments and the influence mechanism of external factors on abnormal heating.

Design and Management of High Voltage Power Systems and Insulation Materials

To satisfy the fast-growing electricity demand, high-voltage power systems with higher performance and better stability are required, which raises challenges including the design of power systems, the control of high-power electronics, the synthesis and preparation of high-performance insulation materials, evaluation of the insulation conditions, dielectric insulation tests, material modification, environment protection, etc [...]

Influences of crystallization temperature on the structure, dielectric, and energy storage characteristics of KBaSrNb5O15‐based glass–ceramics

AbstractGlass–ceramics capacitors have great application potential in pulsed power systems, due to ultrafast discharge speed and high dielectric breakdown strength (BDS). Here, lead‐free niobate glass–ceramic dielectric materials were synthesized, and the effects of heat treatment temperature on the dielectric, ferroelectric, and energy storage properties of glass–ceramics were investigated comprehensively. The results exhibit that the dielectric permittivity first increases and then decreases as the crystallinity increases; however, the dielectric BDS diminishes. At the optimum crystallization temperature of 740°C, the maximum value of discharge energy density is 2.2 J/cm3 at 600 kV/cm, which is about 7.6 times that of mother glass. Furthermore, an ultrahigh power density of about 380.9 MW/cm3 and ultrafast discharge speed of about 11.2 ns were achieved simultaneously. Meanwhile, great thermal stability of charge–discharge property was verified in this glass–ceramics. According to P–E loops and dielectric test result, a high dielectric constant (∼207) and low dielectric loss (&lt;0.005) as well as high energy storage efficiency of about 94.9% were achieved for G740 sample. The previous results make the obtained glass–ceramic as potential candidates in dielectric capacitors.

High dielectric permittivity and ultralow dielectric loss in Nb-doped SrTiO3 ceramics

In this study, we prepared a series of Nb-doped SrTiO3 ceramics sintered in both air and N2 atmospheres. The X-ray diffraction (XRD) analysis indicated that all samples had a pure cubic phase perovskite structure with no secondary phase. The dielectric test showed that the Nb-doped SrTiO3 ceramics had a high dielectric permittivity (>3 × 104) and low dielectric loss (<0.004) over a broad temperature range from −100 to 300 °C with a breakdown strength over 20 kV/cm. The dielectric performance is attributed to the designated TiTi′−VO··−TiTi′ deep-lattice-defect states localising weak-hopping electrons to generate high defect-dipole concentrations, as verified by systematic X-ray photoelectron spectroscopy (XPS) experiments. This study offers a route for designing other types of high dielectric permittivity ceramics.

Comparison of test methods for pinhole and non-uniform defects in nitrile examination gloves

Mechanical and dielectric integrities of 4-g (0.07 mm thickness) nitrile-examination gloves with defects such as sub-mm pinhole and thin spot in the obscured finger region, as well as relatively large thin area, are measured and compared. Mechanical test methods were the water-leak test and the tensile test. In complaince to EN455 standard, a normal glove is required to pass the force-at-break of 6 N in the tensile test, but this was significantly reduced (<3 N) with the presence of above mentioned defects. Similarly, from the electrical insulation test, the dielectric breakdown voltage was reduced from around 800 V to as low as 20–40 V at the pinhole or thin spot. Based on the failure results, we compare the efficacies of water-leak, tensile and the electrical-insulation test methods. This work suggests that the electrical insulation test is suitable for real-time monitoring in the production line.

Evaluating the potential of using foamed concrete as the insulation layer for pavements in cold regions

Insulated pavement structures help prevent frost penetration and its negative impacts on roadways and airfields in cold regions. The most commonly used insulating material in pavements is extruded polystyrene (XPS) boards. However, the utilization of XPS boards has several unavoidable drawbacks such as degradation due to long-term moisture infiltration. For this reason, there is an increasing interest to explore alternative materials such as tire chips, bottom ash, and foamed glass aggregates as the insulation layer. This paper aims to evaluate the potential of using foamed concrete as an insulation layer. To achieve this goal, a thermo-mechanical (TM) coupled model was developed to simulate the responses of insulated pavement with a foamed concrete insulation layer. In addition, the compressive strength and thermal conductivity of different densities of foamed concrete were tested to provide the material parameters for the developed model. The model was then calibrated by a large-scale insulated pavement test. The calibrated model was used for a parametric study to reveal the influence of the thickness, depth, and density of the foamed concrete layer on the thermal and mechanical performance. Simulation results show that the developed model can accurately predict the thermal performance of insulated pavements. Compared with the performance of uninsulated pavements, the foamed concrete -insulated pavement has better performance in resisting frost effect and traffic loading. The parametric study also found that a minimum thickness exists for a foamed concrete insulation layer to ensure the subgrade layer is unfrozen. Increasing the thickness, depth, and density of a foamed concrete layer enhances its mechanical performance.

Formation of a robust Cu adhesive layer on poly(ether ether ketone) via self UV-initiated surface polymerization

Owing to the rapid increase in the demand for miniaturized flexible circuit devices, such as flexible copper clad laminate (FCCL), the development of a polymer substrate capable of adhering to the Cu film without deterioration of the dielectric properties is becoming a challenging issue. This study presents a process for forming a robust Cu adhesive layer on poly(ether ether ketone) (PEEK) while preserving the thermal, mechanical, and dielectric properties of PEEK. By simple UV irradiation without any precise control, the benzophenone group in PEEK chain structure can produce free-radicals (self UV-initiated polymerization). Using this principle, 2,3-epoxypropyl methacrylate and 3-tri(methoxysilyl)propyl methacrylate were copolymerized on the PEEK surface (PEEK-g-Polymer). The peel strength of the Cu adhered PEEK-g-Polymer, measured by a 90° peel test, was 9.40 N/cm, which satisfies the required value for FCCLs. The differential scanning calorimetry, tensile, and dielectric tests confirmed that the thermal, mechanical, and dielectric properties of PEEK were preserved after the polymer grafting process, and the dielectric loss of PEEK-g-Polymer was lower than that of commercial polyimide-based substrate. This straightforward approach is expected to make a great contribution to achieving lower dielectric loss and miniaturization for 5G devices.

Performance enhancement of polyurethane foam applied to optical fiber microphones.

The application of polyurethane foam to optical fiber microphone sensitization is proposed. In this experiment, the Michelson interference system is used, and polyurethane foam is coated on the optical fiber of the signal arm. By changing the optical fiber material of the signal arm and the reference arm, four sets of comparative experiments are designed to test the sensitivity of the optical microphone. Through a scanning electron microscope (SEM) test and a pore size distribution test, the porous structure and non-closed cell structure characteristics, pore size range, etc., of the polyurethane foam were determined. The average sound absorption coefficient of the polyurethane foam is 0.66 through the sound absorption coefficient and sound insulation test. The sound absorption coefficient of each frequency band is above 0.2, the sound insulation is below 30 dB, and the overall sound insulation performance is poor, which can be regarded as an ideal sound absorption material. The sound-absorbing effect of polyurethane foam is better than that of nylon tight-packed materials in the frequency range of 500-2800 Hz, and it has a significant sensitization effect in this frequency band. In the frequency band above 2800 Hz, the sound-absorbing effect of nylon tight-packed optical fiber is better than that of polyurethane foam, and the optimal combination is determined by lateral comparison as signal arm (nylon tight-packed fiber + polyurethane foam) + reference arm (bare fiber). Finally, with different coating thicknesses as variables, the results show that the optical fiber microphone has the best sound collection effect when the coating thickness of polyurethane foam is 1.5 cm.

Power Interference Suppression Method for Measuring Partial Discharges under Pulse Square Voltage Conditions

Partial discharge (PD) is an important metric for the insulation diagnosis of power equipment. However, its detection is affected by the strong electromagnetic interference generated by pulse square voltage. We therefore propose a power interference suppression method for partial discharges under pulse square voltage based on a quadratic measurement method. We conduct analysis of the topology circuit when partial discharge occurs in the insulation test sample and introduce the basic principle of the secondary measurement method according to the superposition principle and the linear relationship between the square voltages at different peak values. We verify the feasibility of this method by simulating a PD signal with power interference. Subsequently, we use the successive interception comparison method to solve the non-correspondence of the two initial measurement points problem and design and manufacture the transformer turn-to-turn oil-paper insulation test sample and experimental tank. By measuring the PD starting voltage of the insulation test sample under the power frequency voltage, we determined the first measurement voltage under the pulse square voltage and obtained the signal x1(t) to subsequently measure the PD signal x2(t). According to the proposed successive interception comparison method, the signal x1(t) is processed, and the secondary measurement method suppresses the power interference of the measured signal x2(t). We demonstrate that the proposed method effectively suppresses the power interference in PD detection under a pulse square voltage.

Vapor cooling of a structural skirt for a large-scale hydrogen tank

The demonstration of vapor cooling on a structural skirt was one of the main objectives of the Structural Heat Intercept, Insulation, and Vibration Evaluation Rig (SHIIVER) testing. SHIIVER consisted of a 4-meter diameter stainless steel tank with an aluminum forward skirt. The forward skirt was cooled by directing effluent vapor from the tank through two flow channels that each went 360 degrees around the interior of the skirt in a helical pattern. Flow rates, temperatures, and pressures in the system were measured allowing for the calculation of heat load removed via cooling stream and heat load reduction into the tank. Testing occurred at fill levels between 25% and 90% full using both liquid hydrogen and liquid nitrogen. Boil-off rate was varied independent of the skirt performance by adding multilayer insulation over the spray-on-foam insulation on the tank domes, while leaving the barrel insulated only with spray-on-foam. The results from the testing, which demonstrate vapor cooling removed heat flow from the tank flange and reduces total propellant heat load by as much as 19%, are analyzed and discussed.

Study on Irradiation Effect of Insulating Materials for Fusion Superconducting Magnet: Effect of Low-temperature Irradiation

The purpose of this study is to investigate the change in dielectric performance in the direction of parallel to layers due to the difference in γ-ray irradiation temperature, irradiation atmosphere, and absorbed dose. γ-ray was irradiated using a 60Co source at room temperature, in liquid nitrogen, and in liquid nitrogen temperature gas atmosphere in the absorbed doses of 0, 5, and 10 MGy, respectively, and the dielectric breakdown tests were conducted at room temperature using a high-voltage breakdown tester. To investigate the mechanism of the change in dielectric strength, the density and electron spin resonance (ESR) measurements of the specimens were carried out. After irradiation at room temperature, the dielectric strength increased slightly with the increase in the absorbed dose. The reason for this may be that the molecular density increased due to the promotion of cross-linking reaction by recombination of molecules and reaction of unreacted epoxy groups by γ-ray irradiation. After irradiation in liquid nitrogen, the dielectric strength decreased significantly at 10 MGy, while after irradiation in liquid nitrogen temperature gas atmosphere, the dielectric strength slightly decreased with the increase in absorbed dose. These results suggest that, at low temperature, the freezing of molecular motion limits the movement of radicals generated by irradiation, and that the decomposition reaction is dominant against the crosslinking reaction.

Research on Turn-to-Turn Insulation Test of Dry-Type Air-Core Reactor

The dry-type air-core reactor insulation detection is the key component of reactive power compensation and filter device, which needs to be tested. At present, there are few researches on detection method of dry-type air-core reactor insulation. Based on the principle of pulsed voltage method and reducing test cost, the mathematical model of dry-type air-core reactor is established, the actual parameters are entered for simulation analysis. The simulation results verify the feasibility of using the pulse voltage method to detect the turn insulation between the dry-type air-core reactors, which can guide the actual dry-type air-core reactor insulation detection method.