Frequency Domain Dielectric Spectroscopy Research Articles

Dielectric response characteristics and moisture exposure evaluation of oil-paper insulation based on microstrip ring resonator

Moisture ingress significantly accelerates the aging of oil-paper insulated equipment, making accurate assessment of moisture content critical for the operation and maintenance of oil-immersed insulated power equipment. In this paper, a novel method for rapid moisture content evaluation is proposed based on a microstrip ring resonator (MRR) designed with a fundamental frequency of 1.16 GHz. A calculation model for the dielectric response analysis using MRR is established to characterize dielectric properties of the material layered on the substrate. ANSYS HFSS electromagnetic simulation software was used to study the impact of dielectric material thickness and the substrate on the MRR test results. Experimental measurement demonstrated that the maximum deviation in resonance frequency was merely 0.542 %. The dielectric properties of uniformly and non-uniformly damp insulating pressboard were analyzed across the frequency band from 1 to 6 GHz. The MRR test results were compared with those of the standard resonant cavity method and frequency domain dielectric spectroscopy (FDS) test. Using the regression algorithm and curve analysis, moisture assessment models for both uniformly and non-uniformly damp oil-paper insulation were established. The experimental results show that the MRR test can clearly distinguish between the pressboard samples with varying moisture levels under uniform conditions, with a maximum moisture evaluation error of 8.19 %. The results demonstrate that the MRR test method, requiring only 56 s, can quickly and effectively evaluate the moisture content of insulating pressboard.

Assessing the moisture content of oil‐impregnated paper bushings with a simple and fast method

AbstractPower outages can cause harm to both society and individual health. Among the crucial elements of power systems, power transformers play a vital role, and their failures can lead to incidents and disruptions. According to statistics, almost 50% of the explosions and fires in the power transformer are caused by oil‐impregnated paper (OIP) bushing failures. Moreover, moisture is a crucial factor that affects the health of OIP bushings, and assessing the moisture level in OIP bushings is vital to guarantee the safety of power systems. While the frequency‐domain dielectric spectroscopy (FDS) method has been widely used to assess the moisture content of OIP bushings on‐site, it has the disadvantage of requiring a long measurement time. Therefore, a novel technique was proposed in this study that involves measuring the OIP bushing dissipation factor (tanδ) at 1 Hz to estimate the moisture content in a significantly shorter time. Five samples of OIP with various moisture levels have been selected, and an equation based on the OIPs' value of tanδ at 1 Hz was proposed to assess the moisture level of OIP bushings. Furthermore, the validity of the proposed method was successfully verified, proving its precision and time efficiency.

Analysis and aging evaluation method of frequency domain dielectric spectroscopy for high-voltage XLPE submarine cables

Analysis and aging evaluation method of frequency domain dielectric spectroscopy for high-voltage XLPE submarine cables

A Fast Dielectric Response Measurement Instrument With Dynamic Power Supply Tracking and Active Suppression of Temperature Fluctuations

This paper proposes a fast frequency domain dielectric spectroscopy (FDS) test scheme for diagnosing oil-paper insulation. The high-voltage output section introduces dynamic power supply tracking (DPST) and cascading techniques to generate high-voltage excitation signals. The DPST can increase the amplifier's voltage slew rate (SR) from 13 V per microsecond to 36.3 V per microsecond without crossover distortion. In the micro-current measurement section, the error active suppression structure of bias current and bias current under time-varying temperature conditions is proposed to improve the temperature stability of the measurement circuit. The fast testing technology shortens the test period by 65% in the low-frequency band by using the method of multi-frequency signal synthesis and partial cycle waveform fitting. The experimental results show that the total harmonic distortion and noise (THD+N) of the output voltage of the instrument are less than or equal to 0.078%. The voltage range is 780 Vpp. The standard deviation of current is less than 1.5%, and the standard deviation of tan δ is less than 1.7%, which verifies the stability of the designed instrument.

Frequency‐Domain Dielectric Response of Insulating Paper with High Humidity

AbstractThe frequency‐domain dielectric spectroscopy (FDS) of humid insulating paper has been measured at different temperatures. The data show three independent dielectric processes: electrode polarization, hopping conductivity and interfacial polarization. The dielectric properties of humid insulating paper are composed of hopping conductivity and interfacial polarization, and its equivalent dielectric model can be represented by a Havriliak‐Negami (HN) relaxation branch parallel hopping conductivity. At high temperatures and low frequencies, the measured dielectric spectroscopy bends downward, which is caused by the electrode polarization. In this case, the equivalent dielectric model is composed of the body impedance of insulating paper and the electrode polarization in series. According to the equivalent dielectric model, the components of electrode polarization, hopping conductivity, and interface polarization can be separated, thereby eliminating the parasitic effect of electrode polarization on the dielectric properties of insulating paper. Both of hopping conductivity and interface polarization of insulating paper move toward high‐frequency direction with temperature increasing. For humid insulating paper with a moisture content of 5.9%, the activation energies of hopping conductivity and interface polarization are 1.18 and 0.99 eV, respectively. This difference in activation energies results in the inability of the spectrums of insulating paper to overlap with each other at different temperatures. Based on the insulating paper without oil immersion, the results obtained in this article are not affected by oil or oil‐immersion operations. This provides a reference for exploring the dielectric properties and physical mechanisms of oil‐paper composite insulation materials widely used in high‐voltage equipment. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

An Impulse Aging Assessment Method for Arrester Under Multiple Strokes Based on Frequency Domain Dielectric Spectroscopy

Multiple strokes (MS) is the primary factor leading to the failure of electrical equipment. Arrester, as the critical lightning protective instrument, its service status is directly relevant to the stability of transmission system operation. Meanwhile, MS also significantly accelerates the impulse aging of arresters and ultimately causes malfunction. This paper proposes a method to evaluate the impulse aging of arresters under MS based on frequency domain dielectric spectroscopy (FDS). Firstly, MS experiments are performed, and then the FDS parameters of arresters are measured. Subsequently, the improved Havriliak–Negami equation (IHNE) is developed to explicitly analyze the dielectric relaxation process of arresters. Additionally, an improved metaheuristic algorithm is presented to identify the parameters in IHNE based on FDS, which has significant parameter identification. Eventually, the impulse aging evaluation model is established. Simultaneously, the condition of two types of arresters (including new and used arrester in service on transmission lines) are estimated based on the evaluation method presented in this paper. The maximum absolute errors are 0.73 times and 1.2 times, respectively, fully validating the effectiveness of the presented method. The investigation of this paper can provide a direct foundation for the replacement and overhaul of line arresters.

Degree of polymerisation estimation for insulation paper immersed in silicone oil using frequency domain dielectric spectroscopy

AbstractFrequency domain dielectric spectroscopy (FDS) is an effective method reflecting the changes of ageing status of silicone oil‐immersed insulation paper. For better evaluating the ageing status of silicone oil‐immersed insulation paper, an evaluation method was studied by analysing the ageing kinetic model and results of FDS. First, the method to separate the different polarization losses and conductivity loss from the results of FDS was studied. Then, based on the idea of ageing correction translation coefficient and time‐varying pre exponential factor, the zero order ageing dynamic model was modified, which combines the ageing kinetic model with the results of FDS. Finally, the evaluation method for the degree of polymerisation (DP) of silicone oil‐immersed paper was proposed, and experiments were conducted to obtain the parameters in the modified model and then to verify the proposed method. The results show that the proposed method can be used to evaluate the DP effectively.

Parameter Extraction for the Degradation of On-Board Arrester in High-Speed Railway Under Effects of Multiple Strokes

On-board arrester (OBA) is an essential equipment of electric multiple units (EMUs), and its working condition will directly affect the reliable operation of EMU. Simultaneously, due to frequent multiple strokes (MSs), OBA suffers from accelerated impulse deterioration and serious life threatening. Thus, this article extracts the feature parameters for degraded OBA under effects of MS. First, an experiment platform is established to perform the MS experiment. The dc parameters and frequency-domain dielectric spectroscopy (FDS) parameters of OBA are then measured. Subsequently, the measured data and the reliability of experimental results are discussed. Finally, microscopic feature parameters [i.e., barrier height (BH) and depletion layer width (DLW)] and dielectric feature parameters of OBA are extracted, and their effectiveness is verified (the maximum and mean of absolute relative error are merely 5.14% and 2.76%, respectively). The results demonstrate that: 1) with increasing MS aging, DLW and BH descend gradually, and after 30 MSs, the maximum decreases are 64.5% and 82.28%, respectively; 2) the geometric capacitance and third polarized branch capacitance ascends exponentially with the deepening of impulse aging, while the insulation resistance and relaxation time constants drop exponentially; and 3) several microscopic and dielectric feature parameters are extracted to effectively evaluate the degradation state of OBA.

Dielectric Measurements in the Frequency Domain—Dos and Don'ts

This article provides an overview of frequency domain dielectric spectroscopy measurements and the techniques for data analysis. Examples are used to illustrate key points in formulating the experiments and analyzing the data.

Parameters Extraction and Mechanism Analysis of the Moisture in Oil–Paper Based on the Spectral Decomposition of Dielectric Response

Frequency-domain dielectric spectroscopy (FDS) is widely used in the insulation assessment of oil-immersed power equipment, and the moisture in insulating paper could be qualitatively predicted by mathematical approximation. However, due to the still lots unexplored underlying mechanisms, until now, there is still no convincing and physical method for the diagnosis of moisture content. With the aid of spectral decomposition methods, this article aims to explore the effects and mechanism of moisture on the independent dielectric response spectra. First, the measured dielectric response curve is unfolded and reconstructed by derivation of the real part curve. Second, the independent polarization and conductance spectra of damp samples are extracted, and then, the relationships between moisture content in insulating paper and spectral parameters are established quantitatively. The results show that moisture introduces a new polarization in the midfrequency region at room temperature, and both polarization and conductance increase with the moisture content. The multiple adsorption model and the proton exchange model of moisture are employed to illustrate the changes of the polarization and the conductance spectra, respectively. This research provides a methodological reference for the moisture assessment of oil–paper insulation.

Correlations between physico-chemical properties and dielectric behavior of thermally aged XLPE cables insulation

The carried out investigations aim at clarifying the correlations between physico-chemical properties and the variation of dielectric losses of Cross-Linked Polyethylene (XLPE) as Medium Voltage cable insulation during thermal aging. The used cables were manufactured by ELSEWEDY CABLES. They have been installed in Algeria where they must resist high temperatures that could exceed 50 degrees in the south of the country. For this aim, thermal aging measurements were performed on XLPE cables samples at 80, 100 and 140 °C for aging time of 5000 hours. The chemical properties were evaluated through Fourier Transform Infrared Spectrum (FTIR). In addition, the effect of aging on the crystallinity ratio, the lamellar thickness and the melting peak temperature was assessed using Differential Scanning Calorimetry (DSC). Frequency domain dielectric spectroscopy has been conducted on the aged XLPE cables in order to study the evolution of the dielectric losses. The obtained results showed that the principal aging mechanism is thermal oxidation which heads to deteriorate the morphology and increase both the polarization and losses, principally at low frequencies. It has been found that the color changes caused by the chains scission indicate the increase of interfaces between the cable insulating and semi-conductive layers, which could head to increase the dielectric losses due to the interfacial polarization.

Time and frequency domain dielectric spectroscopy for in-situ and ex-situ determination of amorphous fractions of isothermally cold-crystallized Polylactic acid

Time and frequency domain dielectric spectroscopy for in-situ and ex-situ determination of amorphous fractions of isothermally cold-crystallized Polylactic acid

The Study of VFTO Distribution in the Insulation System of IOCT Used in Traction Network

The FDS (Frequency-domain Dielectric Spectroscopy) of oil-immersed insulation paper, and semi-conductive paper with different moisture content, has been measured. The data measured are fitted as a function of frequency and moisture content using the amendatory Cole–Cole model utilizing the least square technique. Then, the broadband MTL model of the insulation system of IOCT (Inverted-type Oil-immersed Current Transformer) is established considering the capacitive electrodes thin layer, and the distribution parameters consider the moisture and frequency dependence. A new method for VFTO (Very Fast Transient Overvoltage) distribution calculation of insulation systems is proposed.

Simultaneously improving the electrical properties and long-term stability of ZnO varistor ceramics by reversely manipulating intrinsic point defects

Excellent electrical properties and the improved long-term stability of ZnO varistor ceramics were simultaneously achieved by doping NiO. The microstructural features were investigated using X-ray diffractometer, scanning electron microscopy, and energy dispersive spectroscopy, while the intrinsic point defects were characterized using frequency domain dielectric spectroscopy and verified by photoluminescence and Raman spectra. The results indicated that in the ZnO varistor ceramics, a reverse manipulation of donor point defects, i.e., suppressing mobile zinc interstitial but increasing stable oxygen vacancy, was achieved. The long-term stability of NiO-doped ZnO ceramics was improved via a decrease in zinc interstitial density, with a degradation rate of 0.064 μA cm−2 h−0.5. Meanwhile, due to an increase in oxygen vacancy density, the excellent nonlinear current–voltage performance, i.e., a high nonlinear coefficient (72.9), low leakage current density (0.08 μA cm−2), and low grain resistivity (13.43 × 10−3 Ω m), was maintained. The findings of this study provide a possible method for developing high-performance ZnO varistor ceramics by manipulating point defects.

Comparison of the Dielectric Properties of Ecoflex® with L,D-Poly(Lactic Acid) or Polycaprolactone in the Presence of SWCN or 5CB.

The main goal of this paper was to study the dielectric properties of hybrid binary and ternary composites based on biodegradable polymer Ecoflex®, single walled carbon nanotubes (SWCN), and liquid crystalline 4′-pentyl-4-biphenylcarbonitrile (5CB) compound. The obtained results were compared with other created analogically to Ecoflex®, hybrid layers based on biodegradable polymers such as L,D-polylactide (L,D-PLA) and polycaprolactone (PCL). Frequency domain dielectric spectroscopy (FDDS) results were analyzed taking into consideration the amount of SWCN, frequency, and temperature. For pure Ecoflex®, two relaxation processes (α and β) were identified. It was shown that the SWCN admixture (in the weight ratio 10:0.01) did not change the properties of the Ecoflex® layer, while in the case of PCL and L,D-PLA, the layers became conductive. The dielectric constant increased with an increase in the content of SWCN in the Ecoflex® matrix and the conductive behavior was not visible, even for the greatest concentration (10:0.06 weight ratio). In the case of the Ecoflex® polymer matrix, the conduction relaxation process at a frequency ca. several kilohertz appeared and became stronger with an increase in the SWCN admixture in the matrix. Addition of oleic acid to the polymer matrix had a smaller effect on the increase in the dielectric response than the addition of liquid crystal 5CB. Fourier transform infrared (FTIR) results revealed that the molecular structure and chemical character of the Ecoflex® and PCL matrixes remained unchanged upon the addition of SWCN or 5CB in a weight ratio of 10:0.01 and 10:1, respectively, while molecular interactions appeared between L,D-PLA and 5CB. Moreover, adding oleic acid to pure Ecoflex® as well as the binary and ternary hybrid layers with SWCN and/or 5CB in a weight ratio of Ecoflex®:oleic acid equal to 10:0.3 did not have an influence on the chemical bonding of these materials.

An IGBA Algorithm-Based Curve Reconstruction Method of Frequency-Domain Dielectric Spectroscopy for OIP Bushing With Nonuniform Moisture Distribution

Oil-impregnated paper (OIP) bushing is essential equipment in traction power supply systems, and its moisture status is directly related to the power transmission of high-speed railway. Also, the moisture distribution in the OIP bushing insulation is usually nonuniform. The frequency-domain dielectric spectroscopy (FDS) method is now widely accepted as the most potential method for evaluating the moisture status of the OIP traction bushing with nonuniform moisture distribution. However, as far as the FDS curve reconstruction of field bushing is concerned, it remains a challenge. In this article, based on the extended Debye model, a new curve reconstruction method (including equivalent circuit and mathematical models) of the bushing dielectric response is proposed. Then, the reconstruction method is converted into a mathematical problem of programming optimization. Based on the advantages of metaheuristic algorithms such as simplicity, flexibility, derivative-free mechanism, and local optimal avoidance, an improved metaheuristic algorithm was used to address the optimization problem. Finally, the proposed method was tested on bushing samples and real bushings. The research shows that the proposed method of curve reconstruction can well characterize the FDS curves of the traction bushing insulation with the nonuniform moisture distribution.

Biodegradable polymer composites with osteogenic potential

The aim is to study the basic physico-mechanical properties of hydroxyapatite (HA) composites (up to 25–50 wt%) with polylactide (PLA-HA) and poly(e-caprolactone) (PCL-HA) prepared by melt compounding, as well as the osteogenic potential of PLA-HA in vivo . Materials and methods . All biodegradable polymer composites were prepared by hot melt compounding and studied by dielectric spectroscopy in frequency domain, optical microscopy, X-ray diffraction analysis and tensile tests. An ability of PLA-5 wt% HA composites prepared by 3D-printing to induce bone tissue growth in vivo was detected with the help of ectopic subcutaneous test in inbred mice. Results. Values of the real part of complex permittivity of PLA-HA and PCL-HA composites are increased by 15–30% compared to those for initial PLA and PCL, while tand loss factor does not exceed 0.02 for PLA-based composites and 0.2 for PCL-based composites. The crystallinity degree of PLA-HA composites is increased by 3 and 6 times with an increase of HA content from 25 to 50 wt% respectively compared to the indicator for PLA. The crystallinity degree of PCL-HA composites with 25 wt% HA is increased by 2 times compared to the value for PCL. It is due to the fact that HA powder particles play the role of additional nucleation centers. For all this, mechanical strength of composites diminished statistically. Even lowest HA content (5 wt%) in PLA-HA composites prepared by 3D-printing increased the incidence of ectopic osteogenesis by 40%. Conclusion. Designed biodegradable composites have a potential of practical use for bone tissue engineering.

Application of combined gas chromatography and dielectric spectroscopy in SF6 gas insulated high voltage converter transformer bushing insulation performance

High voltage converter transformer bushing is widely used in the outlet part of high-end converter transformer, and its operation safety and stability directly determine the operation effect of converter transformer. The bushing of SF6 gas insulated high voltage converter transformer is a typical multi-media insulation structure. The air end of the bushing includes SF6 gas insulation medium, and the bushing tail is in contact with transformer oil. The bushing body is generally epoxy impregnated paper composite insulation structure. For the complex insulation system, the running state of converter transformer bushing should be monitored in real time. For gas phase insulation, gas chromatography is generally used to dynamically analyze the composition of SF6 gas; for epoxy impregnated paper solid insulation, dielectric spectrum technology is generally used to analyze its wide frequency domain dielectric characteristics. Therefore, the combination of gas chromatography and dielectric spectroscopy technology can effectively characterize the insulation performance of SF6 gas insulated high-voltage converter bushing. In view of this, this paper first gives the basic theory of frequency domain dielectric spectroscopy technology and gas chromatography technology, and further analyzes the current carrying and heating conditions of the central conductor of high-voltage converter bushing under overload and short-circuit conditions. The dielectric spectrum characteristics of the converter bushing core under different temperature conditions are obtained by experiment, and the Cole-Cole model is used for fitting analysis. The decomposition characteristics of SF6 insulation gas in epoxy resin composite insulator under overload and short-circuit conditions are analyzed experimentally, and the variation curve of SF6 characteristic decomposition gas with time is obtained. Combined with the above relationship between gas chromatography and dielectric spectrum, an operational evaluation strategy for the performance of SF6 gas insulated high voltage converter bushing is proposed. In this paper, for the first time, the internal insulation performance of high-voltage converter bushing is comprehensively evaluated by gas chromatography and dielectric spectrum analysis technology for the first time, which has certain theoretical and practical application value for the operation, maintenance and overhaul of converter bushing.

Electrical and Mechanical Condition Assessment of Low Voltage Unshielded Nuclear Power Cables Under Simultaneous Thermal and Mechanical Stresses: Application of Non-Destructive Test Techniques

Low voltage cables play a crucial role in the safe and reliable operation of nuclear power plants. This paper discusses the effect of simultaneous combined thermal and mechanical stresses on the overall insulation of unshielded low voltage power cables used in nuclear power plants. Cable samples based on XLPE/CSPE insulation were exposed to thermal-mechanical combined accelerated aging tests for an extended period lasted to 907 hours. Time and frequency domain dielectric spectroscopy were applied to reveal the degradation level of the core insulation and jacket due to combined stresses. The former technique was conducted through the measurement of the decay and return voltage slopes, while the latter technique was based on the measurement of the complex permittivity. Moreover, the mechanical properties of the cable insulation were investigated by applying the measurement of the Shore D hardness. The results showed that the combined aging affects both the electrical and mechanical properties of the overall insulation. The complex permittivity at 100 Hz, the decay voltage slope, and the hardness had an upward trend with aging, while the return voltage slope showed an inverse trend. In addition, the results of the electrical and mechanical measurements showed strong correlation with aging time and further correlation was observed between the dielectric and mechanical properties. The correlation between aging time and test results suggests that the presented test methods are promising tools for in situ condition monitoring of low voltage unshielded cables in nuclear power plants.

Comprehensive Investigation on Service Aged Power Transformer Insulating Oil After Decades of Effective Performance in Field

Liquid-based dielectrics have been used in the electrical power components for high voltage insulation and cooling purposes for over a century. Numerous condition monitoring techniques are used for its performance analysis. Dielectric breakdown event of insulting oil is a key failure mode which adversely impacts the transformer performance. Transformer oil is a prime source of fault diagnosis of transformer and its condition monitoring. Insulation condition of the oil, acidity, chemical degradation that occurred over the period of time can be detected by modern spectroscopic techniques. Fourier transform infrared spectroscopy (FTIR) has acquired exceptional importance in determining the chemical degradation of the oil for utility professionals. In this work, service aged oil specimens were taken from a transformer with a successful operating life of 37 years in order to investigate the reason behind its internal faults. Various testing techniques such as breakdown voltage, frequency-domain dielectric spectroscopy, UV–visible spectroscopy, charge migration and mobility and FTIR were used for comprehensive analysis of oil condition. For comparative performance analysis, pristine samples of same oil were procured from the identical manufacturer. More emphasis was laid on the capability of FTIR to access the oil condition. The experimental findings of this study could provide a valuable insight to researchers and condition monitoring engineers in this field.