Frequency Dielectric Response Research Articles

Dielectric frequency response at different voltage levels of mineral oil-based silica nanofluids

In this paper, the Frequency domain dielectric response of oil-paper insulation, employing SiO 2 -based nanofluids is reported. It is a well-known fact that the dissipation factor ( tanδ) profile is affected by the magnitude of excitation voltage & measurement temperature. Analysis of data obtained from laboratory samples suggests that the influence of excitation voltage is non-linear in nature. It is further observed that the degree of non-linearity is different for new and aged mineral oil. The frequency domain dielectric response for new mineral oil-based silica nanofluid has been found non-linearity nature at 50 Hz for sinusoidal excitation level 26 V-130 V for temperature range 50⁰C-70⁰C. Similarly, in the case of aged mineral oil, a non-linearity nature has been found at 1 Hz. The related analysis presented in this paper suggests that it is possible to express the non-linearity introduced in the value of dissipation factor ( tanδ) at power frequency by a mathematical expression.

Defect-related broadband dielectric loss mechanisms of Na1/2Sm1/2Ti1–z(Al1/2Nb1/2)zO3 ceramics

Dielectric ceramics with low dielectric loss in the microwave bands are key materials used in fifth/sixth-generation (5G/6G) telecommunication. Exploring the defect behavior and the broadband dielectric response of ceramics is helpful to understand the loss mechanism and develop novel low-loss microwave dielectric ceramics. In this work, Al/Nb was co-substituted for Ti4+ in Na1/2Sm1/2TiO3 (NST) ceramics with a perovskite structure, and the low frequency, microwave and terahertz (THz) dielectric responses were investigated. In different frequency bands, the variations of dielectric loss with substitution amount are inconsistent. The Al/Nb-substitution increases the dielectric loss in the low frequency and microwave bands, while the dielectric loss in the THz band decreases. The changes in dielectric loss are closely related to the lattice defects in Na1/2Sm1/2Ti1–z(Al1/2Nb1/2)zO3 (NST-zAN, 0 ≤ z ≤ 0.1) ceramics, which are studied by thermally stimulated depolarization current (TSDC) technique. The dielectric relaxation of the defects including oxygen vacancies (VO··) and defect dipoles leads to the dielectric loss in the low-frequency and microwave bands. The dielectric loss in the THz band is mainly affected by the damping of lattice vibration, which is associate with the defect concentration. This work might provide a considerable reference for the development of low-loss dielectric materials.

Study of dielectric properties of bio-potential for precursory signature of seismic activities

Sudden changes occur in the environment due to atmospheric variations (seasonal variations, drought, rainfall, humidity, floods and seismic activities) is a matter of discussion. When the sensing was done by nature and human bodies like mammals, animals and trees adopt the abnormal phenomena in the respect of amplitude enhancement and change the behaviour. The seismogenic ULF emissions, plasma anomalies, ionospheric perturbations and bio-electric potential was affected in respected of surrounding environment and helps us in understanding the mechanism of natural hazards. The bio-potential of the internal medium lies in the scope of -90mV to 40 mV relative to the external medium. We used live sensor for observing the D.C. amplitude enhancement (~50 mV) which helps us in analyzing the precursory signature of seismic activities. We have observed the dielectric properties of live sensor (dielectric constant (ε) and dielectric loss (ε’), relaxation time (τ), impedance (Ω), frequency response (f) and conductivity (σ)) of deep rooted trees. These results have been reported here and trying to observed the change in deep rooted trees before-mid-after the commencement of seismic activity having the energy of the order of (M = 0.08 x 108 ergs/sec.) in the form of electromagnetic waves. Due to this effect the internal structure of tree has been changed and shows a strong resemblance between them. We have observed the basic changes in deep rooted trees in the form of change in bio-potential and the results were highlighted the response by analyzing the dielectric properties of the same trees and establishing a profound relation which help us in determining the precursory signature of earthquakes.

Site selective response of cationic dopants in ZnO nanomaterials: Optical, dielectric and magnetic behaviors

Modulations of dielectric response and the investigation of magnetic property due to the percentage variation (3, 5 and 7 wt%) of chromium ion doping in 5 wt% yttrium doped-ZnO nanomaterials are considered in this report. The rods like Cr3+ and Y3+co-doped ZnO nanomaterials with polycrystalline single phase of wurtzite lattice structure are prepared by hydrothermal synthesis route. Frequency and temperature dependent dielectric response of all the co-doped ZnO nanomaterials were investigated in this report and the observation suggests that the dielectric permittivity of these co-doped ZnO nanomaterials can be modulated based on the site selectivity of the cationic dopants like Cr3+ or Y3+in between the lattice sites and the interstitial sites inside the host ZnO lattice structure. In addition, low temperature (10 K) magnetic ordering with ‘S’ shape hysteresis loop are observed. The hysteresis curve has been fitted and contribution of each magnetic phase (paramagnetic and ferromagnetic) has been extracted. This report is not only helpful to understand the modulation of dielectric response of ZnO like semiconducting materials depending on site selectivity of the cationic dopants inside the lattice structure of ZnO but also explore the underlying physics of DMS system consisting of multiple magnetic phases. This study shows that the semiconductors based dielectric materials are more effective for tailor made applications in various dielectric devices.

Ultralow‐k hollow glass microsphere filled perfluoroalkoxy composites

AbstractPerfluoroalkoxy (PFA) composites filled with different volume fractions of hollow glass microsphere (HGM) and HGM/PFA–HGM/HBO3–HGM/PFA sandwich layered composites were prepared by simple dry mixing and hot‐pressing process. The dielectric frequency and temperature response characteristics, thermal expansion coefficient, and mechanical strength were investigated as a function of the loading fraction of HGM fillers. The obtained .6VfHGM/.4VfPFA composite demonstrates ultralow‐k (εr ∼ 1,63@1 MHz; 1.57@10 GHz) with low‐dielectric loss (∼7.2 × 10−4@1 MHz; ∼1.73 × 10−3@10 GHz), water absorption of ∼1.21%, in‐plane thermal expansion coefficient of 42 ppm/°C, and temperature coefficient of dielectric permittivity (τεr) of ∼−92 ppm/°C. The temperature stabilities of dimension and dielectric permittivity for the .6VfHGB/.4VfPFA composite could be substantially improved by forming .6VfHGM/.4VfPFA–.6VfHGM/.4VfHBO3–.6VfHGM/.4VfPFA sandwich–layered composite, which still maintained reasonable dielectric properties and mechanical rigidity with flexural strength of ∼8.1 MPa.

Evaluate the effect of graphene and milled glass fibre on the thermal, flame and dielectric properties of silicone elastomer filled with aluminium hydroxide

In this work, the thermal stability, thermal conductivity, dielectric frequency response, smoke factor (SF), fire performance index (FPI), and fire growth index (FGI) of silicone elastomer composites were studied and compared. TGA/DTG results indicated that the addition of graphene nanoplatelets (GNP)/milled E-glass fibres (MGF) improved the thermal stability of silicone composites by increasing the Tmax2, T20% and T30%, whereas thermal conductivity was improved by 93%–115% compared to RTV1 and 12%–24% compared to RTV2. Based on the GNP/MGF loadings, a low relative permittivity and low dielectric loss were observed. Furthermore, GNP/MGF filled silicone composites exhibited high FPI and low FGI, and microstructure analysis revealed a compact bottom char layer with no crevices on the surface. The most promising silicone composites were RTV4 and RTV5, which had higher thermal stability, improved thermal conductivity, excellent FPI and FGI values, and excellent dielectric properties, making them more suitable for electrical outdoor insulation exposed to fires.

A Crystalline Supramolecular Rotor Functioned by Dual Ultrasmall Polar Rotators†

Comprehensive SummaryAs an extended model of conventional molecular rotors, a conceived construction of novel crystalline molecular rotor that simultaneously contains two discrete polar rotators is presented here. The supramolecular self‐assembly of 18‐crown‐6 host and two rotator‐containing ion‐pair guests affords a three‐in‐one cocrystal, (2‐NH3‐iBuOH)(18‐crown‐6)[ZnBr3(H2O)], in which the hydroxyl group and aqua ligand both function as ultrasmall polar rotators. On the basis of the variable‐temperature single‐crystal X‐ray diffraction, variable‐temperature/frequency dielectric response, density functional theory calculations, and molecular dynamics simulations, it is found that such dual polar rotators experience a gradually enhanced rotation with increasing temperature, and more importantly, could be controlled by a reversible polar‐to‐polar structural phase transition, i.e., from a “single‐(polar rotator)” state at low‐temperature phase to a “mixed‐dual‐(polar rotator)” state in the vicinity of transition, and to an unusual “synchronized‐dual‐(polar rotator)” state at high‐temperature phase.

Fingerprints of Critical Phenomena in a Quantum Paraelectric Ensemble of Nanoconfined Water Molecules.

We have studied the radio frequency dielectric response of a system consisting of separate polar water molecules periodically arranged in nanocages formed by the crystal lattice of the gemstone beryl. Below T = 20-30 K, quantum effects start to dominate the properties of the electric dipolar system as manifested by a crossover between the Curie-Weiss and the Barrett regimes in the temperature-dependent real dielectric permittivity ε'(T). When analyzing in detail the temperature evolution of the reciprocal permittivity (ε')-1 down to T ≈ 0.3 K and comparing it with the data obtained for conventional quantum paraelectrics, like SrTiO3, KTaO3, we discovered clear signatures of a quantum-critical behavior of the interacting water molecular dipoles: Between T = 6 and 14 K, the reciprocal permittivity follows a quadratic temperature dependence and displays a shallow minimum below 3 K. This is the first observation of "dielectric fingerprints" of quantum-critical phenomena in a paraelectric system of coupled point electric dipoles.

Nonlinear Dielectric Properties of the Stator and Transformer Insulation Systems

Composite insulation systems usually exhibit nonlinear phenomena, such as voltage-dependent dielectric response and high-order current harmonics. In this article, a high-voltage system capable of performing both dielectric frequency response (DFR) and polarization/depolarization current (PDC) measurements up to 20 kV is devised. The nonlinear properties of the motor stator and power transformer insulation systems are studied. Experimental results show that the voltage-dependent effect becomes significant as the voltage magnitude approaches the nominal and frequency decreases. The third current harmonic component is found to be dominant over the other components and has a strong correlation with the decrease in the dissipation factor. By taking both the fundamental and third-harmonic components into account, more consistent voltage-dependent characteristics are revealed. These features are important indications of insulation defects that are often neglected in field diagnostic testings. The investigation of the nonlinear properties helps to enhance the condition diagnosis reliability.

NSGA-II Model-Based Dielectric Frequency Response Parameters for Aging and Moisture Analysis of Transformer Insulation

The complex dielectric frequency response (DFR) behavior is established during the frequency domain spectroscopy (FDS) test, the methods for extracting the feature parameters to distinguish the diverse response process, as well as achieve the state analysis, still deserve variable attention. To address this, a combination of non-dominated sorting genetic algorithm (NSGA-II) and extended Cole-Cole model is presented to extract the required feature parameters. In the current work, the FDS of insulation samples with various states is first collected. Then, the decoupling analysis is performed on the extended Cole-Cole model to distinguish the diverse DFR behavior. The NSGA-II model is employed to solve the extended Cole-Cole model to obtain the required feature parameters. Finally, the insulation state analysis practiced by lab and field trials proves the feasibility and applicability of the extracted feature parameters. Regarding this, this work reports an intelligent optimization model to be responsible for a more accurate and reliable state analysis of transformer insulation via the extracted feature parameters.

Low frequency dielectric response mechanism of bamboo charcoal

The carbonization of bamboo at 400 °C–700 °C resulted in the formation of graphite crystals embedded in amorphous carbon. The high dielectric constants (≈103 at 1 Hz) of these carbon materials were attributed to the presence of polar groups such as -OH, -NH2 and -COOH with marginal contribution from interfacial polarization. The dielectric constants were observed to be frequency-dependent and found to be decreased with increasing frequency. The measured dielectric loss was also found to be decreasing with increasing frequency. Conductance dominant dielectric loss observed in 400 °C–600 °C annealed samples was further supported by the Cole-Cole plot. Maxwell–Wagner–Sillars interfacial polarization relaxation along with conduction loss was observed only for the 700 °C annealed sample.

Effect of Rice Husk Filler on the Structural and Dielectric Properties of Palm Oil as an Electrical Insulation Material

This study uses natural fibre, which is moisture absorbent, as an innovative and economical filler for insulating oil. Rice husk (RH) is a natural fibre known to have water-absorbing properties and used as a supplementary cementitious material. This research utilises the water-absorbing properties of RH to improve the physicochemical and dielectric properties of insulating oil. RH was refined into a fine powder at a diameter of less than 63 µm. Palm oil (PO) was synthesised with RH at concentrations of 0 g/L, 0.01 g/L, and 0.1 g/L. The moisture-absorbent properties of RH were analysed by using Fourier-transform infrared (FTIR) spectroscopy. The particle size and distribution of RH in PO were also obtained using a scanning electron microscope (SEM) and a Zeta particle analyser. The breakdown voltage (BDV) strength of PO with RH was measured according to IEC 60156, and the dielectric frequency response was investigated in the range of 102–105 Hz. RH is proven to absorb moisture from PO, as the O–H band intensity at the 3350 cm−1 is increased from the experimental results. Therefore, the mean BDV and dielectric insulation properties of PO dispersed with RH also increased accordingly.

Frequency Dielectric Response of Aramid Enhanced Cellulose Paper in Aspect of Its Water Content Determination

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

Coupling of ethanolamine ammonia-lyase protein and solvent dynamics characterized by the temperature-dependence of EPR spin probe mobility and dielectric permittivity.

Electron paramagnetic resonance (EPR) spectroscopy is used to address the remarkable persistence of the native Arrhenius dependence of the 2-aminopropanol substrate radical rearrangement reaction in B12-dependent ethanolamine ammonia-lyase (EAL) from Salmonella typhimurium from physiological to cryogenic (220 K) temperatures. Two-component TEMPOL spin probe mobility in the presence of 10 mM (0.08% v/v) 2-aminopropanol over 200-265 K demonstrates characteristic concentric aqueous-cosolvent mesodomain and protein-associated domain (PAD, hydration layer) solvent phases around EAL in the frozen solution. The mesodomain formed by the relatively small amount of 2-aminopropanol is highly confined, as shown by an elevated temperature for the order-disorder transition (ODT) in the PAD (230-235 K) and large activation energy for TEMPOL rotation. Addition of 2% v/v dimethylsulfoxide expands the mesodomain, partially relieves PAD confinement, and leads to an ODT at 205-210 K. The ODT is also manifested as a deviation of the temperature-dependence of the EPR amplitude of cob(II)alamin and the substrate radical, bound in the enzyme active site, from Curie law behavior. This is attributed to an increase in sample dielectric permittivity above the ODT at the microwave frequency of 9.5 GHz. The relatively high frequency dielectric response indicates an origin in coupled protein surface group-water fluctuations of the Johari-Goldstein β type that span spatial scales of ∼0.1-10 Å on temporal scales of 10-10-10-7 s. The orthogonal EPR spin probe rotational mobility and solvent dielectric measurements characterize features of EAL protein-solvent dynamical coupling and reveal that excess substrate acts as a fluidizing cryosolvent to enable native enzyme reactivity at cryogenic temperatures.

Influence of Water Molecules on Polarization Behavior and Time–Frequency Dielectric Properties of Cellulose Insulation

Oil-immersed power transformer plays an important role in power transmission and transformation engineering. Moisture is one of the important factors to determine its insulation performance. Molecular simulation technique is used to study the mechanism of water molecules on the micro polarization behavior of cellulose insulation materials. The number of hydrogen bonds, solubility parameters, total dipole moment and polarizability are analyzed. These characteristics explain the action mechanism of water molecules on cellulose insulation. At the same time, the time domain and frequency dielectric response of cellulose insulation materials with different moisture content are explored. The dielectric modulus spectrum is introduced to replace the traditional frequency dielectric spectroscopy to characterize the micro relaxation process of cellulose insulation under different moisture content. Finally, the characteristic parameters are extracted from the polarization, depolarization current and dielectric modulus spectrum curves to evaluate the moisture content of cellulose insulation materials. The results show that the number of hydrogen bonds, binding energy density, solubility parameter, total dipole moment and polarizability increase with the increase of water content. It should be noted that dielectric modulus spectroscopy can effectively characterize the relaxation behavior of cellulose insulation materials. The moisture content of cellulose insulation can be quantitatively evaluated by DC conductivity, insulation resistance, imaginary part relaxation peak of dielectric modulus and integral value of real part and imaginary part of dielectric modulus.

Synergistic enhancement effect of moisture and aging on frequency dielectric response of oil-immersed cellulose insulation and its degree of polymerization evaluation using dielectric modulus

Oil-immersed cellulose insulation is the heart of the power transformer, which will will gradually deteriorate in the operation process of transformer. Therefore, accurately evaluating the aging condition of the oil-immersed cellulose insulation is important for maintaining safe and stable operation of transformer. In this paper, the synergistic effect of moisture and aging on frequency dielectric spectroscopy (FDS) of oil-immersed cellulose insulation was analyzed in depth using the modified cole–cole model. A novel degree of polymerization (DP) evaluation method for oil-immersed cellulose insulation based on the dielectric modulus analysis and its curve translation method was proposed. Results show that the higher the moisture content and the lower the DP, the greater the frequency dielectric parameters, the smaller the α relaxation time, the greater the DC conductivity and hopping conductivity of the oil-immersed cellulose insulation. The novel DP evaluation method for oil-immersed cellulose insulation based on calculating the integral area of the imaginary part of dielectric modulus A(DP–mc%) and translating the A(DP–mc%) curve was proposed, which could simultaneously consider the synergistic effect of moisture and aging on FDS. The novel DP evaluation method for the oil-immersed cellulose insulation is suitable for moisture range is 0.5–5%, and the DP range is 250–1300. The verified effectiveness of the novel DP evaluation method presents that it is ideal for transformer aging condition assessment, which is superior to the existing evaluation methods.

Ageing state identification and analysis of AC 500 kV XLPE submarine cable based on high‐voltage frequency dielectric response

Carrying out the insulation condition measurement and analysis is important for the safe operation of the submarine cable. In this study, the high-voltage frequency dielectric response is used to identify the ageing state of the AC 500 kV cross-linked polyethylene (XLPE) submarine cable. The complex capacitance and tanδ in the low-frequency area for the new, thermal ageing, electro-thermal ageing cable all increase with the testing voltage increased from 200 to 2000 V. It is founded that the dielectric response at high voltage is more likely to detect the ageing differences. Based on the carbonyl index and the dielectric loss of the XLPE specimens at different position of the insulation layer, the non-uniform ageing phenomenon of the cable insulation is presented for the thermal ageing and electro-thermal ageing cable. The loss quantity parameter and its changing behaviour with testing voltage based on the frequency dielectric response could be used to identify the ageing state. The comparison of the modified Cole–Cole model parameter under 200 and 2000 V also indicates that the higher voltage dielectric response is helpful to identify the ageing differences.

VLF Dielectric Response and HF Localized Dielectric Discharge Measurement for Rotating Machine Insulation Assessment

This paper represents the very low frequency (VLF) dielectric response and high frequency (HF) localized dielectric discharge measurement for rotating machine insulation assessment. The integral conditions of stator winding insulation, the so-called aging condition, were investigated by the dielectric response measuring technique. The polarization and depolarization currents in the VLF range from 0.0001 to 1 Hz were measured under an external step electric field. The local conditions of stator winding insulation, the so-called weak spot condition, were examined by the partial discharge (PD) measuring technique. The PD pulse currents were detected by a capacitive sensor in a wide-band range, where the bandwidth of the measuring system was set between 30 kHz and 30 MHz. The medium voltage rotating machine rated 6.6 kV and 240 to 2,270 kW under different service conditions, i.e., new stator winding, moisture contamination, dirt contamination as well as thermally and severely aged insulation, was studied. Besides, four case studies on measuring the PD in service rotating machines rated 11–15 kV, 7100 to 211,000 kW as well as the attenuation of the PD pulses were conducted and demonstrated. With several case studies, this paper introduces new dielectric parameters, the so-called charge ratio (QR) and charge difference gradient (QDG), to identify the dielectric mechanism occurring in the stator winding insulation caused by the polarization and conduction processes. It can be concluded that the proposed parameters are a valuable tool for assessing the aging condition. In the case of the PD measurement, it was found that the PD pulse is strongly attenuated in the slot section. This paper also introduces the combination of both the dielectric response and PD measurement results, which can be very useful for assessing a complete insulation condition in the rotating machine. Moreover, the criteria for insulation conditions are suggested in this paper to evaluate the integral and local conditions for the rotating machine insulation. The local discharge in the machine causes electromagnetic waves, which may get released from the non-perfect characteristics of the enclosure. This signal may interfere with the functioning of other nearby electronic devices, especially the communication equipment. Therefore, maintaining the excellent condition of the insulation system by the proposed technique detailed in this paper will support the highly effective operational efficiency of the communication system as well.

Terahertz Dielectric Spectroscopy Based Thermal Aging Analysis of Polypropylene

Polypropylene (PP) is a widely used common type of polymer with excellent chemical and mechanical properties. Thermal aging is a main culprit in degrading its lifetime and effectiveness. In this article, terahertz (THz) dielectric frequency response of PP during the process of thermal aging is monitored and analyzed to understand the underlying mechanism and to qualify THz dielectric spectroscopy as a useful tool for time-stamping and benchmarking the thermal aging of polymer materials. Using an improved THz material parameter extraction algorithm for thin films, the real and imaginary parts of the dielectric permittivity of standard PP test coupons were obtained at various stages of the thermal aging process. In agreement with theoretical analysis based on a molecular-level understanding of the thermal aging dynamics, the experimental results indicated THz wave transmission loss of PP correlated quantitatively with the degree of its thermal aging.

Dielectric dispersion and ac conductivity behavior in tin-modified lead zirconate antiferroelectric single crystals

Frequency and temperature dielectric response and electrical conductivity behavior around the antiferroelectric–paraelectric phase transition temperature were studied in PbZr0.93Sn0.07O3 antiferroelectric single crystals. The contribution of conductive processes to dielectric relaxation for the studied frequency range is discussed, considering oxygen vacancies and electronic transport. The relaxation processes below the transition temperature are associated with short-range polaronic hopping due to the interaction of the charge carriers (trapped electrons) with the distorted crystal lattice. Based on the specific coupling between electrons and phonons in the largely distorted oxygen octahedral sublattice of PbZr1−xSnxO3 crystals, an attempt to explain the formation of the incommensurate phase was undertaken.