This paper reviews the main features of acoustic emission technique. First, the characteristics of acoustic signals and their physics are addressed. Then, the structure of acoustic sensors employed ...for capturing signals is studied. In the next step, the acoustic method of PD measurement is compared with the standard electrical method. Afterward, the applications of AET in PD measurement in different equipment are summarized. All acoustic method and combined acoustic-electrical method for PD localization in transformers are discussed. Moreover, the applications of AET in the monitoring of GIS systems are explained, along with the acoustic behaviors of moving particles in these systems. Finally, the general considerations in the signal processing of the acoustic signals are reviewed.
Faults diagnosis in power transformers has been traditionally based on the insulation resistance measurement, polarisation index, analysis of dissolved gasses in oil, dissipation/power factor ...measurement, and partial discharges within many other alternatives. Originally, all these techniques presented an offline implementation, that is, with the transformer out of service. Currently, some of them, such as partial discharges measurement or gas analysis (gas chromatography), are carried out online in those cases in which the importance of a machine justifies it. These techniques have been recently complemented with new alternatives, such as frequency response analysis, an offline application technique. At the same time, in recent years, development of online diagnostic strategies has been carried out only based in monitoring of electrical variables. These techniques have the advantage of being economical in relation to traditional ones. Its development are incipient and with high growth potential. This study presents a review of the most important techniques and a critical comparison between them.
Off-line PD measurement is important for GIS. Interference signal generated by frequency-tuned resonant test set has a huge impact on PD measurement. Damped alternating current (DAC) voltage has been ...widely used in field testing of power cable and has no power interference. Whether the DAC can be used for PD testing of GIS still needs to be studied. The particle on insulator can greatly reduce the dielectric strength compared to clean condition, which is a very destructive defect. In this paper, the PDIV of AC and DAC were measured, the number of discharges per cycle was counted, and the PRPD pattern was obtained. For the defect model we set up, test results show that PDIV is independent of waveform and frequency; PD distribution area and the number of PDs per cycle increase with frequency. This is because SF 6 gap needs to recover its dielectric strength after discharge. When the recovery time and discharge interval are on the same order, it's possible to excite PD at a lower voltage, thereby increasing the number of PDs in each cycle. DAC is effective for detecting the defect of particle on insulator in GIS, and the PD activity of DAC is more obvious.
The poor electronic and ionic conductivities of covalent organic frameworks (COFs) severely restrict the development of COF‐based electrodes for practical rechargeable batteries, therefore inspiring ...more research interest from the direction of both material synthesis and technology. Herein, a dual‐porous COF, USTB‐6, with good crystallinity and rich redox‐active sites is conceived and fabricated by the polymerization of 2,3,8,9,14,15‐hexa(4‐formylphenyl)diquinoxalino 2,3‐a:2′,3′‐cphenazine and 2,7‐diaminopyrene‐4,5,9,10‐tetraone. In particular, the heterogeneous polymerization of the same starting materials in the presence of graphene affords uniformly dispersed COF nanosheets with a thickness of 8.3 nm on a conductive carbon substrate, effectively enhancing the electronic conductivity of the COF‐based electrode. Such a graphene‐supported USTB‐6 nanosheets cathode when used in a lithium‐ion battery exhibits a specific capacity of 285 mA h g−1 at a current density of 0.2 C and excellent rate performance with a prominent capacity of 188 mA h g−1 at 10 C. More importantly, a capacity of 170 mA h g−1 is retained by using the USTB‐6 nanosheets cathode after 6000 cycles charge and discharge measurement at 5 C.
A sophisticated covalent organic framework (COF) predesign and synthetic strategy, with the assistance of materials processing technology, results in a new COF‐based high‐performance organic cathode for practical lithium‐ion batteries, with a specific capacity of 285 mA h g−1 at current density of 0.2 C, and retained capacity of 170 mA h g−1 after 6000 cycles at 5 C.
It is well known that a correlation exist between the pattern of partial discharge (PD) behavior and the insulation quality. Since different sources of partial discharge have their own unique effects ...on the degradation of insulation material, it is vital to investigate the relationship between the defect type and the PD to determine the insulation quality. Numerous work had been done to classify partial discharge patterns with variable success. Past research work in partial discharge classification varies greatly in terms of classification techniques used, choice of feature extraction, denoising method, training process, artificial defects created for training purposes and performance assessment. Therefore it is necessary for a literature survey to access the state of the art development in partial discharge classification.
Having been for a long time a mainstay of industrial insulator material defect detection, the measurement of partial discharge patterns has recently been shown to also consist in a reliable tool ...helping with the monitoring of flash sintering. The goal of this work is to develop a bespoke, portable phase-resolved partial discharge (PRPD) measurement system based on microcontroller technology that can monitor partial discharge (PD) activity during the application of growing electrical voltage to a sample that is to be sintered. The system was tested on a custom experimental setup and shown to be able to measure PD pulses from 20 pC to 1000 pC, with a repetition rate of up to 100 ksamples/s above 50 pC and a reduced repetition rate under 50 pC, down to 25 ksamples/s for 20 pC charges. Phase-amplitude-occurrence discharge patterns can be recorded with a phase resolution of up to 1°. When applied to the measurement of PRPD patterns arising in a porous zinc oxide (ZnO) sample subjected to increasing electrical 50 Hz AC voltages from 500 to 2000 V at room temperature, the bespoke system was shown to be able to acquire characteristic patterns matching with those obtained using a comparable commercial system, proving its adequacy for PD monitoring in the context of flash sintering with increased flexibility and at a fraction of the price.
In this paper, the corona discharge in rod-plane air gap under AC-DC composite voltages was measured by non-inductive resistance and MPD 600 partial discharge measurement system. The characteristics ...of corona discharge pulses under AC-DC composite voltages were interpreted by phase resolved partial discharge (PRPD) patterns. The corona discharge inception voltage of rod-plane air gap under AC-DC composite voltages were measured and predicted theoretically. The charge of positive corona discharge is much larger than that of negative corona discharge, and the repetition rate of positive corona discharge is much smaller than that of negative corona discharge, which is due to the difference in the production mechanism of initial electron. The repetition rate and phase distribution range of discharge pulses decrease with the increase of AC component when the amplitude of AC-DC composite voltage is a constant. The weighted pulse sequence analysis (WPSA) was used to analyze the corona discharge pulses under different applied voltages. The WPSA plots of positive corona discharge and negative corona discharge have different characteristics, and the WPSA plots under AC-DC composite voltage have greater dispersion than that under DC voltage. This work provides a new perspective for the analysis of corona discharge pulses under AC-DC composite voltages, which will be helpful to the location and identification of equipment defects under AC-DC composite voltages.
Power cables, the most critical component of the power system, must be extremely reliable in order to avoid revenue losses due to premature failure. The dielectric properties of cable insulation may ...deteriorate due to ageing phenomena, which may have a negative impact on the polymer materials used for insulation. Therefore, the early detection of such depletion, and the severity of degradation while the equipment is in operation, aids in the avoidance of a total failure. Partial discharge (PD) detection and analysis have been adopted as a predictive test to characterize and assess the state of electric cables in advance. This review provides an in-depth discussion of the reactions that occur in the insulation system of the cables. Moreover, this paper presents a comprehensive review of the state-of-the art of various PD detection techniques regarding sensor types. The drawbacks and challenges of different PD measurement techniques have been elaborated. Following that, the numerous PD localization methods are discussed, as well as the necessity of computational intelligence approaches and their pros and cons. Last but not least, the authors provide a deep insight into the theoretical and practical implications of deep learning in PD localization, as well as recommendations for future research directions. This review will provide valuable insights and act as a starting point for researchers to lead the development of more efficient approaches for diagnosing PD in the cable.
In this article, a method is proposed to classify the in-service transformer oil by assessing the level of degradation in oil. Initially, 135 oil samples are classified into Classes 1-3 as per IEEE ...C57.106 (2015) standard by the conventional techniques which require five tests. The proposed method attempts to classify the oil samples by a single nondestructive partial discharge (PD) test measurement. The PD data of the 135 transformer oil samples are represented as 1-D histograms and classified by statistical analysis using histogram similarity measures (HSM) including cross correlation test, Kolmogorov-Smirnov (KS) distances, and chi-square test. This classification technique achieves an accuracy of 94.9%. The results are further subjected to class likelihood measures in the postprocessing stage, and this improves the accuracy of classification to 97.5% establishing the efficiency of the proposed method.
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