Research and Design of a Transmission System for Time-Frequency-Domain Electromagnetic Method

Chapter 14 - Electromagnetic Methods in the Frequency and Time Domains

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This paper deals with recent progress in diagnosis of electric power apparatus using non-conventional partial discharge (PD) measurements; i.e. acoustic signal detection method, electromagnetic wave detection method, and transient earth voltage (TEV) detection method. The author describes simulation technology of electromagnetic (EM) wave propagation and induced surface current, and acoustic wave propagation by PD using finite difference time domain (FDTD) method and finite element method (FEM) for understanding and visualization of the phenomena. Diagnosis and reliability evaluation are also described based on the understanding of the PD induced electromagnetic and acoustic waves propagation, and surface current generated in high voltage equipment such as gas insulated switchgear (GIS), and oil-filled transformers.

The overall objective of this dissertation is to effectively and efficiently obtain some important characteristic functions of acoustic transducers, such as electrical impedance function, transmitting voltage response (TVR) and beam pattern (BP). Oftentimes, one makes measurements on these functions through traditional ways, e.g., stepped harmonic analysis method and Fourier-based analysis method. To improve the accuracy and efficiency of computing these characteristics, new approaches by pole-residue operations are developed and verified in this dissertation. In this new approach, the poles and residues associated with the input and output signals are extracted with the multi-signal Prony-SS method, which is an extension and improvement of the classical Prony’s method. The system functions can be computed by the operations of those poles and residues from input and output signals. Compared with traditional methods, the new one not only turns out effective and computationally efficient but also overcomes the leakage and the frequency resolution problems, by getting a continuous function in the frequency domain without periodic assumption. In addition, many significant characteristics, such as modal frequencies and modal damping, can be precisely calculated from the system poles other than reading them from the plotting of system functions in traditional ways. When a periodic loading excites the linear system, the calculation of transient response is discussed in manuscript 1. Compared with time-domain methods, frequency-domain methods are more computationally efficient when computing the responses of linear dynamic systems. However, frequency-domain methods can only compute the steady-state response instead of the total response. To the author’s best knowledge, the transient response of a dynamic system to arbitrary periodic loading can not be solved analytically. In the first manuscript, a closed-form solution for the transient responses of linear multi-degree-of-freedom (MDOF) systems to arbitrary periodic excitations is derived. By taking advantage of the fast Fourier transform (FFT) algorithm, a very efficient numerical method is developed to compute the transient and total responses of MDOF systems, suitable for both damped and undamped systems. In the newly developed method, the computational time required for obtaining the transient response is much less than that for the steady state response. Three numerical examples are provided in this manuscript to verify the correctness, and demonstrate the effectiveness as well, of the newly developed method. Discussed in the second manuscript is the impedance function, which is very essential for a transducer. The impedance function contains many important characteristics, such as the resonant frequencies, anti-resonant frequencies, and

This study introduces an electromagnetic interference detection technique to increase the immunity of a microcontroller-based system in a complex electromagnetic environment (EME). The detection method is explained. First, the interference in the power supply and at the input port of the microcontroller is detected. The simulation results are achieved in both time domain and frequency domain. The measurement results are obtained to verify the correctness of the detection method and the application of the detection method in the automotive field is presented. The final objective of the work is to ensure that the microcontroller-based system works fast in a normal EME and correctly in a complex EME without adding too much cost.

The fatigue damage accumulation rates of horizontally curved thin walled box-girder bridge have been estimated from vehicle-induced dynamic stress history using rain flow cycle counting method in the time domain approach. The curved box-girder bridge has been numerically modeled using computationally efficient thin walled box-beam finite elements, which take into account the important structural actions like torsional warping, distortion and distortional warping in addition to the conventional displacement and rotational degrees of freedom. Vehicle model includes heave-pitch-roll degrees of freedom with longitudinal and transverse input to the wheels. The bridge deck unevenness, which is taken as inputs to the vehicle wheels, has been assumed to be a realization of homogeneous random process specified by a power spectral density (PSD) function. The linear damage accumulation theory has been applied to calculate fatigue life. The fatigue life estimated by cycle counting method in time domain has been compared with those found by estimating the PSD of response in frequency domain. The frequency domain method uses an analytical expression involving spectral moment characteristics of stress process. The effects of some of the important parameters on fatigue life of the curved box bridge have been studied.

The research of offshore electromagnetic spectrum detection methods is of great significance for improving the utilization of offshore electromagnetic spectrum resources, improving the quality of offshore communications, and controlling electromagnetic spectrum resources. This paper combines the Pierson-Moscowitz (PM) wave spectrum model and the antenna attitude to establish a offshore electromagnetic spectrum distribution prediction model based on the ray tracing method to improve the accuracy of the large-scale offshore electromagnetic spectrum distribution prediction. The influence of the maritime environment and antenna attitude changes on the offshore electromagnetic spectrum is studied. The test data shows that the wave spectrum and antenna attitude have a key decisive effect on the offshore electromagnetic spectrum distribution.

This paper presents focus on physical feature extraction and parameter estimation for satellites in space. In the context of increasingly prominent space security issues, it is necessary to improve the security and protection capabilities of the space system, especially the refined feature extraction and recognition technology of space targets. However, the feature extraction methods based on optical or radar imagery are limited by resolution and observation conditions, making it difficult to extract refined features. This paper is based on the attribute scattering center theory, using high-frequency electromagnetic wave detection method. Through the attribute parameter estimation result of the scattering center, the scattering structure on the space target can be identified and its distribution position can be analyzed, and the structure and size of the typical parts in the space target can be extracted. Aiming at the problem of high parameter dimension and large amount of calculation, an attributed scattering centers parameter estimation method with amplitude and phase separation is proposed, which reduces the time complexity of parameter estimation by an order of magnitude, saves system resources and increases the parameter estimation rate, and the estimation accuracy is better than 90%. In terms of the efficiency and accuracy of parameter estimation from simulation and experimental data, the effectiveness of the proposed method in this paper is verified.

The reliability of electrical energy networks depends on the quality and availability of electrical equipment like power transformers. Local failures inside their insulation may lead to catastrophic breakdowns and might cause high outage and penalty costs. To prevent these destructive events power transformers are e.g. tested for partial discharge (PD) activity before commissioning and currently also during service. The current work deals with the electromagnetic PD detection method, also known as UHF method. The disadvantage of the UHF method is still the missing possibility for a calibration or at least a verification of the sensitivity. The so-called Sensitivity Check might show in future a relation between unconventionally measured UHF quantities to the apparent charge level in pico Coulomb. An important aspect is the attenuation of UHF signals within power transformers which is investigated in this paper.

Due to the seasonal permafrost thawing, the Qinghai–Tibet Highway has a depression and instability of the roadbed. In order to obtain the ablation interface and water content characteristics of seasonal permafrost areas, non-destructive ground penetrating radars using electromagnetic wave detection methods are widely used. Regarding the imaging of the ablation interface in permafrost regions, this paper proposes a high-precision procedure for seasonal permafrost media using waveform difference analysis, electromagnetic wave attenuation attribute calculation and relative wave impedance conversion. It improves the resolution and division accuracy of the imaging. In addition, the study demonstrates a method to calculate the temperature and water content of the ablation zone by mining attenuation attribute, relative wave impedance attribute, absolute instantaneous amplitude attribute and the weighted average frequency attribute parameters under the constraints of the measured data. This method has high accuracy and high efficiency and can be used in the rapid calculation of temperature and water content of seasonal permafrost on the Qinghai–Tibet Highway.

Corrosion of grounding grids can affect the safe and reliable operation of power systems. In view of the corrosion problem of the grounding grid, this paper introduces the corrosion mechanism, which is chemical corrosion and electrochemical corrosion respectively. Then, three common grounding grid corrosion detection methods, such as electric network analysis method, electromagnetic field detection method and electrochemical method, are introduced. On this basis, the advantages and disadvantages of three methods are compared. Further prospects for the corrosion detection technology of the grounding grid are pointed out.

This paper proposes a time-frequency fusion algorithm for voltage transformer insulation aging assessment, aiming to address the limited accuracy of traditional time-domain partial discharge detection methods and frequency-domain dielectric loss methods. The algorithm fuses the time-domain transient characteristics of partial discharge signals with the frequency-domain cumulative characteristics of dielectric loss. It introduces an improved attention mechanism to dynamically adjust feature weights and constructs a mapping between the insulation aging index λ and metering error. Experiments were conducted on a platform built with 10kV and 35kV voltage transformers, collecting 350 sets of samples (including 200 sets of field data and 150 sets of laboratory simulation data). The performance of the proposed algorithm was compared with that of traditional methods. Results show that the proposed algorithm achieves an average evaluation accuracy of 98.5%, an improvement of 9.6% and 9.4% over traditional time-domain and frequency-domain methods, respectively. The average error rate is 0.3%, only one-quarter that of traditional methods. Excellent stability is achieved within the temperature range of 25-55°C and humidity of 40%-80%, with a standard deviation of 0.85%, one-third that of traditional methods. This algorithm accurately quantifies the impact of insulation aging on metering accuracy, meeting the requirements of Class 0.2 high-precision metering.

Experimental investigation for the dynamic mechanical properties of a vertical anisotropically supported rotor

The land-based controlled-source electromagnetic (CSEM) method is an important tool in mapping subsurface resistivity contrast, especially for conductive target embedded in a resistive environment. For resistive targets on land, choosing an appropriate configuration to a specific field observation is quite confusing, due to the lack of systematic comparisons of different methods. We have conducted a comparison between the broadside and inline time-domain CSEM methods, using the short-offset transient electromagnetic (SOTEM) method and multitransient electromagnetic (MTEM) method as representatives respectively. We first compared the resolution of these methods by analyzing the relative target response and the misfit space of the designed models. We found that the inline MTEM method had advantages over the SOTEM method in resolving the thin resistive layer. We have developed a weighted joint inversion scheme to enhance the vertical resolution of the MTEM method. We then applied the methods to the investigation of a giant molybdenum deposit. The orebody, which is the real target of the exploration, does not have a conductivity contrast with its host. However, it sits on top of the granite porphyry, which is resistive compared with its surroundings, and so the granite porphyry becomes the resistive target for EM exploration. The results indicated that both methods are effective in locating large resistive target, yet the MTEM method outperforms the SOTEM method when a thick conductive overburden is presented.

The water-rich zones in the coal fields of Northern China have seriously threatened the safe production of coal mines. It is necessary to accurately locate the deep seated and complex water bodies which are usually located in Ordovician limestone. Due to the relatively high cost of seismic exploration, the development effective electromagnetic detection methods and corresponding data processing techniques for the detection of these water-rich areas becomes a topic for the EM geophysicist. In this study, a method of rapidly estimating the burial depth and undulating morphology of coal bed foundations by employing frequency domain electromagnetic sounding data was proposed. The method uses the overshoot/undershoot phenomenon of the apparent resistivity for the frequency domain electromagnetic measurement to quantitatively determine the burial depth of the northern China coal structure bases. First, the featured frequency points were confirmed, where the overshoot and undershoot effects appeared in the electromagnetic sounding curves beside the borehole drilling sites. Then, the correlation coefficient between the confirmed frequency points and the burial depth of coal seam bed was obtained according to the drilling data. Finally, the burial depth of the coal seam beds in the entire survey area was evaluated based on the correlation coefficient and electromagnetic data. This method was applied in the northern areas of Taiyuan City in Shanxi Province, and achieved good results.