The ultra-high-frequency (UHF) method is efficient in partial discharges (PDs) detection in gas-insulated switchgear (GIS). The features extraction of UHF signals is significant for propagation ...characteristics analysis and PD pattern classification. The PD-induced UHF signals are acquired by the internal UHF sensors in an actual 252 kV L-shaped GIS. The short-time Fourier transform method is applied to process UHF signals and describe the propagation characteristics in L-shaped GIS. Hu's invariant moments of energy density distribution are extracted as features in time–frequency plane. The features are utilised to discriminate different PD defect patterns in actual GIS model by the support vector machine classifier and achieve good results. Finally, a novel system of features extraction and classification of UHF signals is summarised.
Ultra-high frequency (UHF) technique is chosen for partial discharge (PD) detection due to its excellent anti-interference and stability. The existing UHF PD localisation methods are mainly based on ...time-difference technique, that suffer high hardware cost due to the high sampling rate requirement. The wireless UHF sensors together with the scene analysis methods, i.e. received signal strength indicator (RSSI) fingerprint, provide us a low hardware cost and high environmental adaptability solution for PD localisation in substation. The proposed PD localisation method here is divided into two stages. In the offline stage, the RSSI fingerprint map is established by site survey. In the online stage, the position of PD source is estimated by a probabilistic approach. To reduce the influence of noise, the RSSI fingerprints are transformed to a low-dimensional subspace, while the most of redundant noise is discarded. Furthermore, the PD heterogeneity and interference in the offline stage are also discussed and solved by normalisation and clustering algorithm, respectively. A filed test is performed and the results indicate that the mean localisation error is 1.87 m and 82.6% localisation errors are <3 m. The workload in the offline stage is also reduced ∼50%.
Recently, the electromagnetic environment in the UHF television band has changed significantly in Japan. Digital broadcasting has spread, but radio disturbance occur from spring to fall. This ...phenomenon is caused by ionospheric propagation of the Es layer or duct propagation in the troposphere. We have steadily observed UHF radio waves at Ishikawa National College of Technology in Tsubata since 2005. UHF radio waves are received from Matsue city and Korea, which are over-the-horizon distances away from Tsubata. Therefore, we researched the relations between the wave receiving statuses of channels 41, 43, and 45 from Matsue city and the season and weather, and we found that we received the most radio waves in summer and in fine weather. Therefore, this phenomenon may be due to the duct propagations in the troposphere.
The detection of partial discharges (PDs) is vital to evaluate the condition of the insulation systems in high-voltage equipment. Although various methods exist to measure the presence of PD, ...ultrahigh frequency (UHF) approaches have been widely adopted due to their ease of application and their ability to perform measurements without the need for direct galvanic contact with the equipment under test. One of the main challenges with these measurement methods is having sensors with adequate dimensions, bandwidth, and gain, to efficiently measure, in any environment, the electromagnetic (EM) emissions that propagate from the PD pulses even if they are of very low magnitude. This article presents the development of a new bioinspired antenna based on the structural characteristics of the antennae of the Antheraea Polyphemus moth. The bioinspired parameters of the proposed antenna were carefully adjusted to obtain a portable antenna (<inline-formula> <tex-math notation="LaTeX">27.4\times 14.4 </tex-math></inline-formula> cm), with an average gain of 3.07 dBi (between 1.36 and 4.45 dBi) and a bandwidth that covers the entire frequency spectrum, where the most important spectral power contents of PD are emitted (1750 MHz below −10 dB). The results obtained confirm that the proposed antenna is more sensitive than others, such as the Vivaldi antenna or the monopole antenna, commonly used in UHF PD measurements, since it allows accurate temporal and spectral differentiation of the PD pulses, even when the PD is of low magnitude.
This paper presents and characterizes a measurement method for positioning of passive tags, by a drone equipped with a UHF-RFID reader. The method is based on a synthetic aperture radar approach and ...exploits the knowledge of the reader/drone trajectory, which is achieved with a differential Global Navigation Satellite System. Different sources of measurement uncertainty are analyzed by means of numerical simulations and experimental results. The method capabilities are discussed versus the length and shape of the reader trajectory. Finally, the proposed localization method is validated through an experimental analysis carried out with commercial RFID hardware and a microclass unmanned aerial vehicle.
New aspects of UHF PD diagnostics on gas-insulated systems Okabe, Shigemitsu; Ueta, Genyo; Hama, Hiroyuki ...
IEEE transactions on dielectrics and electrical insulation,
2014-Oct., 2014-10-00, 20141001, Letnik:
21, Številka:
5
Journal Article
Recenzirano
Gas insulated switchgears (GIS) have been increasingly introduced as main substation equipment since the late 1960s thanks to their high reliability, safety, and compactness. The UHF method to ...diagnose partial discharge (PD) is broadly employed in the field as an advanced insulation diagnostic technology. There are three primary factors related to the PD signal detection characteristics using this UHF method; namely the frequency spectrum of the PD signal itself inside GIS, the propagation characteristics of the PD signal inside the GIS tank, and the detection characteristics of the sensor measuring the PD signal. Accordingly, to further improvement of the diagnostic technique based on the UHF method, the PD phenomenon itself and its propagation characteristics should be clarified and the measurement system refined. From these perspectives, the present study reviewed the recent and latest findings concerning the PD phenomenon and its propagation characteristics inside GIS as well as the PD measurement system verification methods and diagnostic technologies, and summarized typical examples. Firstly, with regard to the PD phenomenon, measurement up to the high frequency band exceeding 10 GHz (even 30 GHz) clarified that the rise time of the PD current waveform is several tens of picoseconds, shorter than previously known. In the case of PD in micro-defects inside the epoxy insulator, however, the rise time is relatively long, in the order of nanoseconds, and a crack is the most critical defect. Subsequently, with regard to UHF PD diagnostics/monitoring technology, a novel technique using PD current waveform characteristics has been developed, and a more advanced PD diagnostic algorithm has been established by clarifying the influence of the shape and GIS internal structures on the electromagnetic wave propagation characteristics. Less uncertain and simplified calibration and verification technologies are also proposed both for a single UHF sensor and the entire UHF measurement system. These new technologies and further advanced studies in future are expected to make the UHF method more convenient and sophisticated.
In this paper, various ambient energy-harvesting technologies (solar, thermal, wireless, and piezoelectric) are reviewed in detail and their applicability in the development of self-sustaining ...wireless platforms is discussed. Specifically, far-field low-power-density energy-harvesting technology is thoroughly investigated and a benchmarking prototype of an embedded microcontroller-enabled sensor platform has been successfully powered by an ambient ultrahigh-frequency (UHF) digital TV signal (512-566 MHz) where a broadcasting antenna is 6.3 km away from the proposed wireless energy-harvesting device. A high-efficiency dual-band ambient energy harvester at 915 MHz and 2.45 GHz and an energy harvester for on-body application at 460 MHz are also presented to verify the capabilities of ambient UHF/RF energy harvesting as an enabling technology for Internet of Things and smart skins applications.
A high-efficiency CMOS rectifier circuit for UHF RFIDs was developed. The rectifier has a cross-coupled bridge configuration and is driven by a differential RF input. A differential-drive active gate ...bias mechanism simultaneously enables both low ON-resistance and small reverse leakage of diode-connected MOS transistors, resulting in large power conversion efficiency (PCE), especially under small RF input power conditions. A test circuit of the proposed differential-drive rectifier was fabricated with 0.18 mu m CMOS technology, and the measured performance was compared with those of other types of rectifiers. Dependence of the PCE on the input RF signal frequency, output loading conditions and transistor sizing was also evaluated. At the single-stage configuration, 67.5% of PCE was achieved under conditions of 953 MHz, - 12.5 dBm RF input and 10 KOmega output load. This is twice as large as that of the state-of-the-art rectifier circuit. The peak PCE increases with a decrease in operation frequency and with an increase in output load resistance. In addition, experimental results show the existence of an optimum transistor size in accordance with the output loading conditions. The multi-stage configuration for larger output DC voltage is also presented.
A miniaturized ultrahigh frequency (UHF)/ultra-wideband (UWB) dual-band tag antenna with a geometrical dimension of 34.6 mm × 21.5 mm × 6 mm is presented for indoor real-time positioning systems. A ...small patch is employed as the UWB radiator, and two U-shaped striplines are used for the UHF band. A quarter-wavelength metallic strip is introduced under the UWB patch to create an extra resonance to further expand the operation bandwidth. The antenna is backed by a ground plane to reduce the backside radiation and to improve the antenna gain in the UWB band. The measured bandwidth covers the frequency range from 919 to 931 MHz in the UHF band and 3.28 to 6.95 GHz in the UWB band with VSWR better than 2:1. The measured radiation patterns within the above-mentioned UHF and UWB frequency bands are very stable. The attractive features of compact size and wide bandwidth make it a very competitive candidate of tag antenna for indoor positioning systems.
Recently, Ultra-High Frequency (UHF) Partial Discharge (PD) measurements on power transformers has attracted a lot of attention. Despite numerous publications, there are still missing information ...about considerations and limitations of this method in regards to antenna characteristics, relation between IEC 60270 and UHF detection methods and robustness against external noises. In this paper, each of the mentioned sections is investigated in detail by simulation analysis or laboratory measurements. Applying the results obtained in each section leads to a more precise measurement, more accurate analysis of UHF PD data and solving some of the problems associated with it.
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