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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 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]