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In the present study, a HVDC PD test platform with bandwidth of 10 kHz–50 MHz and 250 MS/s sampling rate is built for the ultra-wideband (UWB) detection and investigation of time–frequency (T–F) characteristics of abnormal waveshapes or waveforms in PD pulse sequence. It points out that PD UWB detection systems currently developed resorting to the pulse sequence grouping technology (PSGT) to achieve the PD and noise sources separation were realized by feature extraction of pulse waveforms using T–F map or equivalent T–F method (ETFM), which are based that the single recorded pulse waveforms in time and corresponding frequency domain generated by PD or noise source are regular and stable. Considering the phenomenon that the single recorded waveform in time domain presenting some abnormal patterns such as multi-peaks, continuous discharges and even multi-pulses during 1-2μsin the measured PD pulse sequence, an algorithm for real-time discrimination of abnormal pulse waveform in time domain using threshold moving window (TMW) is designed and approved by the HVDC tests of three typical defect discharge models (corona discharge, inner discharge and surface discharge), which can be used to enhanced applicability for the PSGT mentioned above. While, T–F characteristics of those abnormal waveforms in PD pulse sequences of HVDC tests are shown, which reconfirm that the marked single recorded waveforms in pulse sequence should be excluded for using the PSGT with T–F map or ETFM.

The naturally cooled panel-type radiators are widely used for transformer heat dissipation. However, their poor heat transfer performance also restricts the overall performance of the transformer. The chimney effect can improve the airflow rate due to the thermal pressure difference between the air inside and outside the flow channel, which is widely used to improve the flow and heat transfer of natural convection. In order to improve the heat transfer performance of panel-type radiators under natural convection, a novel radiator is developed, where wind deflectors are added at both lateral sides of the radiator, and a chimney structure is added on the top of the radiator to extend the chimney channel. Then, the fluid flow and heat transfer characteristics inside and outside the radiator are studied by numerical simulation. The results show that cooling air would be effectively sucked into the radiator from the bottom due to the pressure difference generated at the inlet and top of the chimney channel. As compared with the traditional panel radiator without the chimney structure, the airflow on the outer surface of the most cost-effective radiator is increased by 19.14 %, the cooling capacity is increased by 14.76 %, and the oil temperature inside the transformer is reduced to 6.72 °C.

Sulfur hexafluoride (SF6) gas is extensively utilized as an insulating and arc-quenching medium in the circuit breakers and isolating switches of electrical equipment. It effectively isolates the circuits from the atmosphere and promptly extinguishes arcs. Therefore, the issue of SF6 gas leakage poses a significant threat to the related application fields, and the detection of SF6 gas leakage becomes extremely important. Infrared imaging detection offers advantages including non-contact, high precision, and visualization. However, most existing infrared detection systems are equipped with only one filter to detect SF6 gas. The images captured contain background noise and system noise, making these systems vulnerable to interference from such noises. To address these issues, we propose a method for monitoring SF6 gas leakage based on a customized binocular imaging (CBI) system. The CBI system has two filters, greatly reducing the interference of system noise and background noise. The first filter features the absorption resonant peak of SF6 gas. The second filter is used to record background noise and system noise. One aspect to note is that, in order to avoid the interference of other gases, the central wavelength of this second filter should keep away from the absorption resonant peaks of those gases. Accordingly, the central wavelengths of our customized filters were determined as 10,630 nm and 8370 nm, respectively. Then, two cameras of the same type were separately assembled with a customized filter, and the CBI prototype was accomplished. Finally, we utilized the difference method using two infrared images captured by the CBI system, to monitor the SF6 gas leakage. The results demonstrate that our developed system achieves a high accuracy of over 99.8% in detecting SF6 gas. Furthermore, the CBI system supports a plug-and-play customization to detect various gases for different scenarios.

In the present study, a combined in-oil partial discharge (PD) sensor based on oil valve with acoustical emission and ultra high frequency (AE/UHF) methods for PD measurement in transformer is proposed. The combined PD sensor is designed by placing an AE sensor in front of a UHF antenna, and resorting to be fixed on an oil valve to invade inside the transformer to simultaneously couple the AE/UHF signals from PD source. Besides the AE/UHF signals coupling, construction design of the combined PD sensor with oil sealing are shown in particular. And considering the phenomenon of air entering the transformer box due to the improper installation to the oil valve, an installation method using air extraction for the combined PD sensor based on the oil valve is also shown with a discussion on safety and detection sensitivity caused by the sensor insertion depth. Discharge tests in air and insulation defects prove that the combined PD sensor with AE/UHF methods proposed and processed can simultaneously measure or detect the AE/UHF signals produced by PD source effectively with an obvious time difference value Δt, which presents a innovative mixed AE/UHF method of PD measurement for transformer.

High voltage, heavy current, miniaturisation and long service life are the current development trend of high voltage switchgear, which would require high heat dissipation performance for the switchgear. In the present paper, based on the finite element method, the heat transfer in the busbar room of KYN28A high voltage switchgear is numerically studied using the electromagnetic-heat-flow coupling model. The heat dissipation performance in the busbar room under natural convection, forced convection, and using a heat pipe are discussed. Firstly, it is found that natural convection alone cannot meet the demand of increasing the current carrying capacity of switchgear. The temperature rise of the contact inside the contact box is higher than 65 ?, which cannot meet the IEEE standard. Secondly, with the forced convection method, the optimal working flow rate of double groups of a fan is 1.5 m/s, and that of a single group of a fan is 2 m/s. With the same inlet air velocity, the heat dissipation performance is better by using double group fans. Finally, it is found that the overheating problem of the contact system can be solved effectively when the fans are combined with heat pipe, and the heat dissipation performance in the busbar room would be good with low inlet air velocity.

Gas insulated switchgear (GIS) is one of the most important equipment in the power system. Excessive temperature of the GIS busbar conductor will lead to the loss of insulating gas performance and equipment life. In the present paper, based on the finite element method, the temperature distribution and power loss density of a 252 kV three-phase GIS busbar is numerically studied using electromagnetic-heat-flow coupling model, and the structure parameters of the rotation angle, center distance and conductor thickness of the busbar are optimized with Taguchi method. The results show that the conductor thickness has the greatest influence on the maximum temperature and power loss, and the influence proportion is more than 70 %. When the combination scheme of (A1, B5, C5) is adopted, the temperature rises and power loss performance of GIS has been optimized. The maximum temperature is reduced by 9.56 K and the power loss is reduced by 21.7 %. In addition, according to the analysis of the gas breakdown margin, it is found that the SF6 gas still has a good insulation performance after structure optimization. This study is of great significance to the heat transfer and optimization design of three-phase GIS busbar.

Metalens has the advantages of high design freedom, light weight and easy integration, thus provides a powerful platform for infrared detection. Here, we numerically demonstrated a broadband achromatic infrared all-dielectric metalens over a continuous 800 nm bandwidth, with strong environmental adaptability in air, water and oil. By building a database with multiple 2π phase coverage and anomalous dispersions, optimizing the corrected required phase profiles and designing the sizes and spatial distributions of silicon nanopillars, we numerically realized the design of broadband achromatic metalens. The simulation results of the designed metalens show nearly constant focal lengths and diffraction-limited focal spots over the continuous range of wavelengths from 4.0 to 4.8 μm, indicating the ability of the designed metalens to detect thermal signals over a temperature range from various fault points. Further simulation results show that the metalens maintains good focusing performance under the environment of water or oil. This work may facilitate the application of metalens in ultra-compact infrared detectors for power grid faults detection.

In the electric power industry, the requirements for capacity, voltage level and compactness of transformers are getting higher and higher, which lead to significant problems, such as increased loss and more serious hot spots phenomena. Based on the three-dimensional finite element method, this paper establishes the bidirectional coupling between electromagnetic field, flow field and temperature field to calculate the temperature rise of 400 kVA oil-immersed transformer at full load and compare it with the results obtained by the heat-flow unidirectional coupling method (constant loss). The results show, due to the interaction between electromagnetic field and temperature field, the coil loss density increases, but the core loss density does not change. The hot spot temperature of coil increases and the location of coil hot spot changes. The temperature and position of the core hot spot do not change. The loss density of coil decreases as the inlet velocity increases, the hot spot temperature of coil drops faster. When the inlet velocity exceeds 0.5 m/s, increasing the inlet velocity can no longer effectively promote heat exchange. With the increase of the inlet velocity, the interaction between electromagnetic field and temperature field is weakened, but it still has a great impact on the loss density of coil. The multi-physics coupling method is of great significance to improve the accuracy of transformer temperature rise calculation.

Due to the anti-electromagnetic characteristics, high sensitivity and convenient installation, the Fabry-Perot sensor is commonly used in partial discharge detection of transformers. The variations of eigenfrequency and sensitivity caused by membrane temperature would have an important impact on sensor performance. In the present study, the eigenfrequency and displacement response of an intact membrane (IM) and a beam-supported membrane (BSM) under thermal expansion were numerically studied using a thin film vibration model coupled with temperature variations. The influence of the width and length for BSM’s support beam on the stress softening was also analysed. It is found that the thermal expansion of the membrane reduces the stiffness and both the IM and BSM decrease linearly as temperature increases. The IM and BSM will become unstable as temperature increases to a certain value. The thermal stability of the BSM with support beam structure is lower than that of the IM. When the temperature increases, the IM amplitude increases and the BSM amplitude decreases. The eigenfrequency of the BSM is proportional to the width and inversely proportional to the length of the support beam, while the thermal stability is inversely proportional to the width and length of the support beam.

Membrane is the most important element of extrinsic Fabry-Perot interferometer sensors. Studying the relationship between working medium viscosity and membrane vibration characteristics are critical to the sensor design because the transformer oil viscosity will cause viscous loss during membrane vibration. The numerical investigation of membrane vibration characteristics in transformer oil is performed based on the finite element method. Besides, the effect of energy loss caused by viscosity is examined. It is firstly showed that the membrane has the highest sensitivity for the first-order vibration mode, and the transformer oil reduces the fundamental frequency by 60%. Subsequently, when viscosity and heat loss are considered, the amplitude is less than one-fifth of that without energy loss. The viscosity has a more significant effect on the velocity and temperature fields when the vibration frequency is close to the natural frequency. Finally, viscosity has a remarkable impact on the time domain response. Mechanical energy is converted into thermal energy during the vibration and the amplitude will gradually decrease with time. The effect of energy loss caused by viscosity on the membrane vibration characteristics is revealed, which would be important for an oil-immersed membrane design.

Sound sensing finds wide applications in various fields, such as underwater detection, structural health monitoring, and medical diagnosis, to name just a few. Based on our previously developed MEMS-on-fiber sensors, showing the advantages of low cost, small volume, and high performance, a three-dimensional ultrasonic localization system employing four such sensors was established in this work. A time difference of arrival (TDOA) algorithm was utilized to analyze the acquired data and then calculate the accurate position of the ultrasonic signal source. Plenty of practical measurements were performed, and the derived localization deviation in the region of 2 m × 2 m × 1 m was about 2–5 mm. Outside this region, the deviation tended to increase due to the directional sensitivity existing in these sensors. As a result, for a more accurate localization requirement, more sensing probes are needed in order to depict a completely suitable application situation for MEMS technology.

This study describes a novel fiber optic extrinsic Fabry–Perot interferometric (EFPI) ultrasonic sensor comprising a low-cost and high-performance silicon diaphragm. A vibrating diaphragm, 5 μm thick, was fabricated by using the Microelectromechanical Systems (MEMS) processing technology on a silicon-on-insulator (SOI) wafer. The Fabry–Perot (FP) cavity length was solely determined during the manufacturing process of the diaphragm by defining a specific stepped hole on the handling layer of the SOI wafer, which made the assembly of the sensor easier. In addition, the use of cheap and commercially available components and MEMS processing technology in the development of the sensing system, limited the cost of the sensor. The experimental tests showed that the minimum detectable ultrasonic pressure was 1.5 mPa/sqrt(Hz) –0.625 mPa/sqrt(Hz) between 20 kHz and 40 kHz. As a result, this sensor has the potential to successfully detect weak ultrasonic signals.

Extrinsic Fabry–Perot (FP) interferometric sensors are being intensively applied for partial discharge (PD) detection and localization. Previous research work has mainly focused on novel structures and materials to improve the sensitivity and linear response of these sensors. However, the directional response behavior of an FP ultrasonic sensor is also of particular importance in localizing the PD source, which is rarely considered. Here, the directional sensitivity of a microelectromechanical system (MEMS)-based FP ultrasonic sensor with a 5-μm-thick micromechanical vibrating diaphragm is experimentally investigated. Ultrasonic signals from a discharge source with varying incident angles and linear distances are measured and analyzed. The results show that the sensor has a 5.90 dB amplitude fluctuation over a ±60° incident range and an exciting capability to detect weak PD signals from 3 m away due to its high signal–noise ratio. The findings are expected to optimize the configuration of a sensor array and accurately localize the PD source.

A novel beam-supported membrane (BSM) structure for the fiber optic extrinsic Fabry-Perot interferometer (EFPI) sensors showing an enhanced performance and an improved resistance to the temperature change was proposed for detecting partial discharges (PDs). The fundamental frequency, sensitivity, linear range, and flatness of the BSM structure were investigated by employing the finite element simulations. Compared with the intact membrane (IM) structure commonly used by EFPI sensors, BSM structure provides extra geometrical parameters to define the fundamental frequency when the diameter of the whole membrane and its thickness is determined, resulting in an enhanced design flexibility of the sensor structure. According to the simulation results, it is noted that BSM structure not only shows a much higher sensitivity (increased by almost four times for some cases), and a wider working range of fundamental frequency to choose, but also an improved linear range, making the system development much easier. In addition, BSM structure presents a better flatness than its IM counterpart, providing an increased signal-to-noise ratio (SNR). A further improvement of performance is thought to be possible with a step-forward structural optimization. The BSM structure shows a great potential to design the EFPI sensors, as well as others for detecting the acoustic signals.

In order to augment cooling performance of transformer panel-type radiators under natural-convection, the fluid-flow and heat transfer for a novel panel-type radiator and its surrounding air are numerically studied in this paper. The novel radiator is equipped with wind deflectors on both lateral sides and a chimney cap on the top. Then the effects of the height and channel number of the chimney cap on the cooling performance of the radiator are simulated. The results show that wind deflectors can form several enclosed air channels with radiator fins. The airflow can be accelerated under the chimney effect generated in these channels, and the cooling capacity of the radiator can be increased by 12.75%. The addition of a chimney cap can further extend the chimney channels and increase its cooling capacity by 15.74%. Furthermore, with the increase of the height and channel number, the total cooling capacity of the panel-type radiator increases first and then decreases. In this study, when the chimney cap has five channels and a height of 700 mm, the novel radiator can obtain the best cooling performance, where its cooling capacity and overall heat transfer coefficient can be increased by 26.54% and 28.21%, respectively, as compared with traditional panel-type radiators, and the temperature difference between the inlet and outlet insulating oil is 7.1 °C. [ABSTRACT FROM AUTHOR]

In this paper, a digital de PD pulse detection system with bandwidth of 10 kHz-40 MHz is introduced, which was developed using some artificial intelligence methodologies. Focus is made on digital detection, grouping and classification of random pulse signals generated by PD phenomena at dc voltage. Digital detection is developed only resorting to a band-pass filter, a high-speed digitizer (100 MS/s) and a PC with data processing software. Grouping is realized with feature extraction of pulse waveshapes using equivalent time-frequency method (ETFM), making the 2D parameters plane or 3D parameters space, then using the unsupervised clustering Fuzzy C-Means (FCM) method to achieve fast separation for pulse sequence. And classification resorts to least square support vector machine (LS-SVM) based on a fingerprint, which is derivate form 2D histograms of basic parameters, the discharge magnitude q and the time between discharges [DELTA]t of each sub-group. Field application is made for typical defects of oil-paper insulation under dc voltage. At last, several methods to improve separability of the grouping technique are also given for some special cases, including threshold value grouping, marginal coordinates grouping based on 2D parameters plane and grouping using ETFM preprocessed by wavelet denosing. Experimental results show that the dc PD detection system developed with artificial intelligence methodologies is practical and effective. Index Terms--Partial discharge, dc voltage, detection, grouping, classification.

The choice of the materials used as the dielectric media in large transformers continues to be a combination of pressboard and mineral oil. However, a number of failures in the field have been attributed to the surface discharge or creeping discharge over the oil/pressboard interface. This paper reports on an experiment to study surface discharge over oil/pressboard. The TJ (triple-junction) model was used to study the characteristic of partial discharge (PD) from inception to flashover. The max PD charge, pattern, frequency and current pulse were measured during the flashover process. Four oil/pressboard specimens with different aging degrees were used and their influence on the flashover process over oil/paper interface was studied in this experiment. The results indicate that the max PD charge and PD frequency increase with the increase of applied voltage. The oil aging has great influence while the pressboard aging has little influence on PD characteristic over oil/pressboard. The PD pattern and current pulse shape show great difference for various applied voltages. The results therefore suggest that the PD detection on the oil/pressboard can be used effectively to implement the early monitor of surface discharge thereby to avoid the formation of surface flashover. [ABSTRACT FROM AUTHOR]