Frequency Domain Spectroscopy Method Research Articles

Research on Changes in the Phase Shift Angle and Admittance of the Cellulose–Bio-Oil Composite under the Influence of Increasing Moisture during the Long-Term Operation of Power Transformers

In this study, the temperature–frequency dependencies of the pressboard–bio-oil–water nanoparticle composite’s fundamental parameters—phase shift angle and admittance—were examined using the Frequency Domain Spectroscopy method. Measurements were conducted in a frequency range of 10−4 Hz to 5 × 103 Hz at temperatures ranging from 293.15 K to 343.15 K, with a step of 10 K. The temperature stabilization accuracy was less than ±0.05 K. A total of 15 Arrhenius plots were determined for various phase shift angle values, from which 15 values and the average activation energy of relaxation time were determined. Similarly, the values of the activation energy of admittance relaxation time and the activation energy of admittance were determined. It was established that all three average values are identical within the bounds of uncertainty. Based on 45 values, a generalized activation energy was determined, with a value of ΔW ≈ (1.032 ± 0.0196) eV. Using the generalized activation energy value, the phase shift angle curves determined for all temperatures were recalculated to a temperature of 293.15 K. It was found that after conversion, all curves perfectly overlap. A similar operation was carried out for the frequency dependencies of admittance. In this case, too, the recalculated dependencies perfectly match. This means that the shape of the frequency dependencies of the phase shift angle and admittance depends solely on the moisture content in the pressboard–bio-oil–water nanodrop composite. The position of the curves in doubly logarithmic coordinates depends only on temperature and is determined by the generalized activation energy Using the generalized activation energy determined in this study will allow for the development of accurate methods for estimating moisture content in cellulose insulation of power transformers containing bio-oil. This will contribute to the detection of critical moisture content, which is about 5% by weight, and to the elimination of the risk, associated with such a high moisture content, of catastrophic failure of power transformers.

Influence of temperature on frequency domain spectroscopy detection of transformer bushings

Frequency domain spectroscopy (FDS) technology has been widely used to evaluate the insulation state of electrical equipment. However, there are still many in-adaptability when using FDS technology to evaluate the insulation state of transformer bushings. Especially, the result will be affected by temperature in the quantitative diagnosis of moisture degree. The influence of different temperatures on FDS detection data of transformer bushings has been studied to solve this problem in this paper. To obtain the FDS test data curves of transformer bushings at different temperatures, the transformer bushings experiment platform was built in the laboratory. And the bushing samples at different temperatures was measured by FDS detection method, which started at 30 °C and rising at 10 °C intervals until the temperature reached 80 °C. The result shows that the temperature will have a serious impact on the FDS detection data, especially the R0 and C5 in the extended Debye model. To solve the influence of temperature, FDS data correction curves with different temperature has been built in this paper. And its feasibility has been verified by FDS data of transformer bushings with 0% and 1.89% water content. The obtained results can promote the application of FDS method in the evaluation of transformer bushings insulation state.

Quantitative Effect of Aging Duration on Dielectric Parameters Based on Frequency Response

In this work, a non-edible natural ester oil (NEO) is considered for the study for its aging characteristics by the frequency-domain spectroscopy (FDS). The NEO considered is the Jatropha Curcas oil (JAT) because of its non-edible and biodegradable nature. The FDS method is a non-destructive measurement technique which is used to analyze the characteristics of the JAT oil by obtaining the relative permittivity and dielectric dissipation factor (DDF) over a wide range of frequencies. The NEO is subjected to thermal stress in an open beaker aging test setup at 115 °C for up to 500 h, and after every of 100 h of aging, the samples are taken out for testing. This technique is applied to understand the dielectric response of the oil at different aging durations. Fourier transform infrared spectroscopy and ultraviolet visible spectroscopy analyses are implemented before and after aging, to observe the alterations in the structure of the two oil samples. The FDS results show how the dielectric properties of JAT vary under aging and help understand the phenomenon behind the degradation at lower frequencies. The variation in the dielectric properties was analyzed by regression models for a quantitative outlook to aging in the oil samples and an associative relationship is established among the parameters.

Research on Time Saving and Accurate Testing Techniques for Frequency Domain Spectroscopy of Transformer Oil–Paper Insulation

Frequency domain spectroscopy (FDS) is a non-destructive insulation test method that has been widely applied to the insulation evaluation of power transformers. However, a major shortcoming of conventional FDS is the long test duration. Existing studies on accelerated FDS tests suffer from a lack of accuracy and are difficult to apply to field testing. To tackle this problem, a novel FDS test method (named iFDS) is proposed to reduce the duration and improve the accuracy of the oil-paper insulation test. Specifically, the test duration is reduced firstly by signal superposition and waveform prediction. Then, the test accuracy is improved from aspects of the parameters design of excitation, the optimization of the test process, and time-frequency domain data processing. Finally, a test platform is built based on the above methods to implement iFDS testing. To verify the effectiveness of iFDS, the dielectric parameters (Tanδ and C*) of oil-paper insulation were measured using the iFDS platform and compared with that of existing FDS methods in terms of duration and accuracy. Comparative experimental results show that iFDS is a superior method for saving time and accurate testing and has the potential to be versatile for evaluating more insulation objects.

Artificial neural network based method for temperature correction in FDS measurement of transformer insulation

Frequency domain spectroscopy (FDS) measurement has become an important method for the assessment of the condition of the insulation of oil transformers. In recent years, numerous researchers have found that temperature variation affect FDS results. The master curve technique is commonly used to correct the effect of temperature on FDS results. In this paper, an FDS experiment is carried out on a sample transformer. Then, for this transformer, insulation model parameters are determined by using a genetic algorithm based on the FDS results. Then, by using the insulation model parameters, tanδ curves are simulated and compared to real results. Finally, an FDS experiment is conducted on two other transformers at 22 °C, 30 °C, 40 °C, 50 °C, 60 °C, and 70 °C (in order to give sufficient information for a training neural network) and insulation model parameters are calculated via the genetic algorithm. In one of the transformers, the effect of temperature on the FDS curves is corrected by using the master curve technique and the FDS curves are transmitted over the reference curve. It is also shown that the transformer insulation is an Arrhenius-type dielectric. The error of this method is calculated by using a mean square error technique. In the two other transformers, the insulation model parameters related to 22 °C are considered as the target parameters. The insulation model parameters of the other temperatures are fed into an artificial neural network as input, to train it to transfer insulation model parameters related to other temperatures to the reference parameters. Finally, the errors of both methods are compared, and it is shown that this latter method for correcting the temperature effects in the FDS method is the more effective.

Frequency Domain Diagnostics of Transformer Insulation

The first part of paper deals with the base information about diagnostics of power transformers. In this part are presented differently insulating methods, for example method of recovery voltage method, method of polarization and depolarization currents and chromatographic analysis.The second part of paper deals use of method of frequency domain spectroscopy for oil power transformers. This method is used in analysis insulating condition of power transformer with system of oil-paper. It was found, that the results of these tests are highly impacted by the operating temperature during the experimental measurement. Moisture and conductivity between insulating paper and oil in an insulating system are highly dependent from temperature.In the other part, the paper presents experimental results of the frequency diagnostic measurement for a real single-phase traction transformer 110/27 kV at different operating temperatures and states (with oil and without).Finally in the last part, the paper presents comparing frequency insulating measurements among several the same single-phase transformers 110/27 kV.

Analysis of insulation properties of transformer materials at different ambient temperatures

Abstract The first part of paper deals with the base information about diagnostics of power transformers. The second part of paper deals use of method of frequency domain spectroscopy (FDS) for traction transformer. This method is used in analysis insulating condition and its solution has scientific importance for analysis of power transformer with system of oil-paper. It was found, that the results of these tests are highly impacted by the operating temperature during the experimental measurement. Finally, the paper presents experimental results of this diagnostic measurement for a real traction transformer at different operating temperatures and states (with oil and without). It has been found, that moisture and conductivity between paper and oil in an insulating system are highly dependent from temperature.

Bushing failure in power transformers and the influence of moisture with the spectroscopy test

Abstract Distribution and Power transformers and their accessories are the main and important equipment used in the power system, one of their most delicate component is the bushing, and the first failure mode is the moisture. The moisture in the bushing appears in oil-paper (Kraft) insulation, the influence is in the insulation, it acts as a catalyst, due to the insulation degradation and aging. In that way, is very important to detect accurately the presence of humidity and water content within the insulation (oil and Kraft) early as to evade any pre-mature catastrophes. The 2 basic bushing scheme are non-graded and capacitance-graded. The prior is the simplest and the oldest bushing. The capacitance graded bushings are obtainable in four technologies: (i) Epoxy Resign impregnated paper (ERIP), (ii) Resin Impregnated Paper (RIP), (iii) Resin Bounded paper (RB), (iv) Oil-Impregnated Paper (OIP). The last one is the most common bushing. The explosion is the last stage for a failure, it begins with the bushing degradation. The last stage is frequently an expensive and catastrophic failure for the power system, this bushing cannot be repaired. In nowadays, the maintenance routine required a condition check, however, the traditional methods, for capacitive bushing, are inspections, capacitance, PFs, for non-capacitive are watts dissipated and inspections. In this research a study with a possibility of frequency domain spectroscopy (FDS), as frequency domain techniques (FDT), the measurements is developed, for bushings in the inductive equipment, and the limit failure has been done. An important knowledge contribution to the moisture in the bushing has been developed and the needed to update the international standards IEC 60137, IEC 60296, IEC 60422, ASTM D 3487 and ASTM D1305, it is one of the main points in this paper. On the other hand, the electrical capacity such as FDS is ideal, because of its straightforwardness and pragmatism. The goal of the research is to study and investigates the claim of FDS method and its swaying features under site acceptance test (SAT), condition using OIP model with disparities as temperature, aging rate and the conductivity for oil and paper. Finally, the research proposes new limits for bushing in power transformers, likewise, the assessment of this assets with a new update in the internationals standards.

Dielectric losses in the composite cellulose–mineral oil–water nanoparticles: theoretical assumptions

The paper presents an analysis of test results by Frequency Domain Spectroscopy (FDS) of the loss tangent (tgδ) in electrotechnical pressboard impregnated with insulating oil and containing nanoparticles of water depending on the frequency of alternating current, sample temperature and degree of moisture. We found tgδ reduction in areas of low and ultra-low frequency. It is associated with relaxation due to the hopping conductivity (tunnelling) of electrons between moisture nanoparticles occurring in the cellulose impregnated with insulating oil. In frequency areas close to the local minimum of tgδ and higher, relaxation does not depend on the moisture content and is associated with other polar molecules which are part of the cellulose. We developed a new method converting experimental frequency dependence of the loss angle tangent, measured by the FDS method to the reference temperature of 293 K (20 °C), using the exponential dependence of the relaxation time on the temperature, was developed. The activation energy of the relaxation time was determined based on the loss angle tangent of moist electrotechnical pressboard impregnated with insulating oil. It was found that the variation in moisture content in the composite cellulose–mineral oil–water nanoparticles do not cause changes in the activation energy of the relaxation time. The conversion of experimental frequency dependence of the loss angle tangent determined by the FDS method to the reference temperature of 293 K (20 °C) eliminates the temperature dependence in the areas of ultra-low and low frequencies occurring in the runs made directly on the basis of the measurement results. After calculating the frequency dependence of the loss angle tangent to the reference temperature, all that remains is its dependence on the moisture content.

Permittivity of a composite of cellulose, mineral oil, and water nanoparticles: theoretical assumptions

The paper presents results of testing permittivity of an oil-impregnated electric pressboard containing water nanoparticles depending on AC frequency, moisture content level and the temperature of samples. A new method has been developed for converting experimentally obtained frequency dependences of permittivity determined with the frequency-domain spectroscopy (FDS) to the reference temperature of 293 K (20 °C) using exponential dependence of the relaxation time versus temperature. Activation energy of the permittivity relaxation time has been determined for a moist oil-impregnated electric insulation pressboard. It has been established that variations of the moisture content level in a composite of cellulose, mineral oil, and water nanoparticles do not cause any changes in the relaxation time activation energy value, neither in energy states of electrons in potential wells nor in the structure of water nanoparticles. It has been also found that the conversion of experimentally obtained permittivity versus frequency dependences determined with the FDS method to the reference temperature of 293 K (20 °C) eliminates temperature dependences that occur in characteristics based directly on measurement results. Once the relative permittivity is converted to the reference temperature it is only its dependence on the moisture content level that remains.

Terahertz Conductivity of Overdoped Y1−x Ca x B2Cu3O7−δ

In the current work we have investigated the terahertz response of Ca overdoped YBaCuO thin films using both time and frequency domain spectroscopy methods. For both methods a basic data analysis was performed using the two fluid and a variable dielectric function (VDF) models. The imaginary part of the conductivity was proportional to 1/ω, known from the delta-function response. The real part of conductivity showed a well known frequency and temperature dependence, where it increases below Tc and obtains maxima at about 50 K. However, a sharp decrease of the real part of the conductivity was observed at about 10 cm−1. This decrease occurs below Tc and becomes dominant as temperature decreases. It was observed on the 5% and 10% Ca doped samples but it was more dominant on the 10% case. Moreover, this sharp decrease in σ2(ω)at 10 cm−1 was not observed in optimally doped YBCO samples. We would like to stress at this point that these values are much smaller than those obtained by Microwave and Tunneling measurements, arguing for the existence of a complex order parameter in the overdoped regime with an imaginary component of about 1.8 meV.

Diffusion theory of slow responses

When an action is applied to a macroscopic substance, there is a particular sort of slow response besides the well-known fast response. Using diffusion theory, the characteristics of slow response in dielectric, elastic, piezoelectric, and pyroelectric relaxation may be explained. A time domain spectroscopy method suitable for slow and fast responses in linear and nonlinear effects is given. Every relaxation mechanism contributes a peak in differential spectroscopy, and its position, height, and line shape show the dynamical properties of the mechanism. The method of frequency domain spectroscopy is suitable only for linear fast response. Time domain spectroscopy is another nonequivalent powerful method. The theory is confirmed by a lot of experimental data.