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Early warning for transformer faults is valuable for maintenance decision-making. However, limited work has been done in this area due to the difficulty of the model establishment. This paper proposes a two-stage feature extraction method for early warning of power transformer faults. By combining feature ranking and genetic programming (GP), a novel feature extraction process is presented. In the first stage, the data is labeled as normal and fault states and the feature extraction is evaluated on the data. Then, extracted key features and their growth rates are relabeled as normal and warning states. The feature extraction process is evaluated again on relabeled data. Obtained features and logic expression can be used for early warning. The proposed framework can implement an early warning with about 100 days in advance for transformer faults and is verified through 8 sequences of data. The comparisons with two recently reported methods show the superiority of the proposed method.

Supplementary data including supplementary materials and methods.

Purpose:The tumor immune microenvironment (TIME) has an important impact on response to cancer immunotherapy using immune checkpoint inhibitors. Specifically, an “infiltrated-excluded”/“cold” TIME is predictive of poor response. The antidiabetic agent metformin may influence anticancer immunity in esophageal squamous cell carcinoma (ESCC).Experimental Design:We analyzed matched pre- and posttreatment ESCC specimens in a phase II clinical trial of low-dose metformin treatment (250 mg/day) to evaluate direct anti-ESCC activity and TIME reprogramming. Follow-up correlative studies using a carcinogen-induced ESCC mouse model were performed with short-term (1 week) or long-term (12 weeks) low-dose metformin (50 mg/kg/day) treatment.Results:In the clinical trial, low-dose metformin did not affect proliferation or apoptosis in ESCC tumors as assayed by Ki67 and cleaved caspase-3 immunostaining. However, metformin reprogrammed the TIME toward “infiltrated-inflamed” and increased the numbers of infiltrated CD8+ cytotoxic T lymphocyte and CD20+ B lymphocyte. Further, an increase in tumor-suppressive (CD11c+) and a decrease in tumor-promoting (CD163+) macrophages were observed. Metformin augmented macrophage-mediated phagocytosis of ESCC cells in vitro. In the ESCC mouse model, short-term metformin treatment reprogrammed the TIME in a similar fashion to humans, whereas long-term treatment further shifted the TIME toward an active state (e.g., reduction in CD4+ FoxP3+ regulatory T cells) and inhibited ESCC growth. In both humans and mice, metformin triggered AMPK activation and STAT3 inactivation, and altered the production of effector cytokines (i.e., TNFα, IFNγ, and IL10) in the immune cells.Conclusions:Low-dose metformin reprograms the TIME to an activated status and may be a suitable immune response modifier for further investigation in patients with ESCC.

Performance evaluation of optimization-based antenna design methods is essential. It is desirable to develop an efficient test suite with characteristics of antenna structures to replace the high computational cost electromagnetics (EM)-based evaluation. In this article, four typical antennas with respect to four typical objectives based on EM $S$ -parameter simulations are systematically investigated. Based on the investigation results, we propose a performance evaluation test suite allowing efficient and versatile benchmarking for antenna $S$ -parameter optimization algorithms. The test suite consists of eight analytical functions (four unimodal functions, two multimodal functions, and two compositional functions). Each function matches a typical landscape of the EM-simulated antenna problems in the 2-D case. Seven of the functions are scalable to high-dimension problems. The performances of six widely used global optimization algorithms are evaluated using the test suite. The performance evaluation results are compared to those obtained using the two EM-based antenna problems (a single antenna and a multiantenna). The results using the proposed test suite for all six optimization algorithms are consistent with those of the real EM antenna problem. The time cost for performance evaluation using the test suite is only a fraction of the cost using the real EM antenna problems.

Improving the accuracy of transformer dissolved gas analysis is always an important demand for power companies. However, the requirement for large numbers of fault samples becomes an obstacle to this demand. This article creatively uses a large number of health data, which is much easier to obtain by power companies, to improve diagnosis accuracy. Comprehensive investigations from the view of both data set and methodology to deal with this problem are presented. A data set consists of 9595 health samples and 993 fault samples is used for analysis. The characteristics of the data set and the influence of the health data on diagnostic accuracy are discussed. The performance of many state‐of‐art algorithms that handle the imbalanced problem is evaluated. Meanwhile, an efficient fault diagnosis algorithm named self‐paced ensemble (SPE) is presented. In SPE, classification hardness is proposed to include the data characteristic in the classification. This method can guarantee the diversity of the data set and keep high performance. According to the experiment results, the superior of SPE is confirmed and also proves that involving more health samples can improve transformer diagnosis when fault data are limited.

This communication presents a novel surrogate-assisted quasi-Newton enhanced global optimization (SA-QNEGO) algorithm. In this proposed method, the heuristic hypersphere sampling (HHS) method is used to obtain representative samples. The surrogate model is built based on the low-fidelity model. The quasi-Newton enhanced differential evolution (DE) method is designed to optimize the surrogate model. Finally, the optimal design of a high-fidelity model is obtained through a space mapping procedure. The proposed algorithm is verified through two antenna design examples including a dipole antenna with balun and an SIW cavity-backed slot antenna. The results show that the proposed algorithm finds a more accurate minimum value with less computational time than direct optimization using DE.

Hazardous waste incineration residue (HWIR) is categorised as hazardous waste due to the presence of heavy metals such as Zn, Cu, and Cr. Based on the abundant components of silica, aluminium oxide, iron oxide, and calcium oxide in a HWIR from an environmental protection corporation in China, a 100% HWIR was used to prepare SiO2–Al2O3–Fe2O3–CaO glass-ceramic samples. The results showed that Zn, Cu, and Cr present in the glass-ceramic samples were effectively immobilised through the melting–sintering process. Among the four parameters of heat treatment, crystallisation temperature played the most significant role. The glass-ceramic that was formed under optimal conditions contained haematite, pseudobrookite, and anorthite, and exhibited a superior compressive strength, volume density, and water absorption of 204.84 MPa, 2.80 g/cm3, and 1.20%, respectively. Compared with the raw HWIR sample, the leaching concentrations of Zn, Cu, and Cr from the prepared glass-ceramic samples decreased significantly, and their immobilisation efficiencies exceeded 99%. Physical encapsulation in the glass-ceramic samples along with ion exchange in the amorphous glassy matrix and iron-rich crystalline phases were the main immobilisation mechanisms of Zn, Cu, and Cr.

Litz wire has been an essential component for the power electronic design to reduce the eddy loss. However, there is a lack of efficient numerical algorithms to simulate Litz wires due to their complex structures. This letter proposes a multilevel partial element equivalent circuit method that significantly improves the efficiency of the simulation of the Litz wire. This method boosts the simulation efficiency at both packing level and twisting level. In the packing level, a novel meshing method is proposed to capture the skin and the proximity effect accurately and efficiently. In the twisting level, the calculation is further divided into wire level and multipole level, where filament approximation and fast multipole method are unitized, respectively. Taking advantage of symmetry and memory replication, the proposed method is significantly faster and more economical than reported electromagnetic algorithms. The efficiency and accuracy of the proposed method are validated through comparison with popular toolkits and the measurement of two Litz wires with dozens and hundreds of wire strands, respectively.

Purpose: The tumor immune microenvironment (TIME) has an important impact on response to cancer immunotherapy using immune checkpoint inhibitors. Specifically, an “infiltrated-excluded”/“cold” TIME is predictive of poor response. The antidiabetic agent metformin may influence anticancer immunity in esophageal squamous cell carcinoma (ESCC). Experimental Design: We analyzed matched pre- and posttreatment ESCC specimens in a phase II clinical trial of low-dose metformin treatment (250 mg/day) to evaluate direct anti-ESCC activity and TIME reprogramming. Follow-up correlative studies using a carcinogen-induced ESCC mouse model were performed with short-term (1 week) or long-term (12 weeks) low-dose metformin (50 mg/kg/day) treatment. Results: In the clinical trial, low-dose metformin did not affect proliferation or apoptosis in ESCC tumors as assayed by Ki67 and cleaved caspase-3 immunostaining. However, metformin reprogrammed the TIME toward “infiltrated-inflamed” and increased the numbers of infiltrated CD8+ cytotoxic T lymphocyte and CD20+ B lymphocyte. Further, an increase in tumor-suppressive (CD11c+) and a decrease in tumor-promoting (CD163+) macrophages were observed. Metformin augmented macrophage-mediated phagocytosis of ESCC cells in vitro. In the ESCC mouse model, short-term metformin treatment reprogrammed the TIME in a similar fashion to humans, whereas long-term treatment further shifted the TIME toward an active state (e.g., reduction in CD4+ FoxP3+ regulatory T cells) and inhibited ESCC growth. In both humans and mice, metformin triggered AMPK activation and STAT3 inactivation, and altered the production of effector cytokines (i.e., TNFα, IFNγ, and IL10) in the immune cells. Conclusions: Low-dose metformin reprograms the TIME to an activated status and may be a suitable immune response modifier for further investigation in patients with ESCC.

Photovoltaic (PV) systems are susceptible to lightning strikes. During a lightning strike, an induced overvoltage is generated in the PV system. This overvoltage can damage the inverters connected to the dc cables. In this article, a comprehensive study is presented to address the installation issues that will influence the induced voltage between the +dc and –dc cables in the PV system. By using the partial element equivalent circuit method, the skin effect and ferromagnetic property of the mounting structures are well modeled. The wiring in the PV module is also considered in the simulation. The influences of the mounting systems, lightning protection systems, PV frames, and dc cable arrangements are thoroughly investigated. The simulation results and discussions provide guidance for PV structure design for maximizing lightning protection performance without adding additional protective devices.

In this letter, we propose an efficient hybrid sampling method for microwave component modeling and optimization. The sampling method adaptively chooses samples from global and local samples to form a data set. The local samples are obtained using a greedy-like sampling method to exploit potential optimal solutions. The global samples are chosen using random sampling with minimum distance rejection to ensure the uniformity of the samples in the design space. The obtained data set is used to establish a surrogate model using the artificial neural networks (ANNs), and the optimal design parameters are obtained by optimizing the ANN model. A bandstop microstrip filter is taken as an example to verify the performance of the sampling method. The results show that the ANN model based on the proposed method achieves better modeling performance and yields better optimal design than the ANN model based on conventional sampling methods.

Designing an efficient shield using simulation requires an expansive computational cost due to large ratio of width to thickness. This paper presents a two-level surrogate based optimization process to efficiently design multilayered shields. The method first exploits space-filling sampling to obtain a global optimal start point. The coarse model is then adopted to be the first-level surrogate. Two-dimensional (2-D) simulation is selected as the coarse model to avoid the time consuming high-fidelity 3-D calculation. Sequential design is followed where response surface approximation (RSA) is applied to construct the surrogate of the coarse model. The evaluation time of the RSA is negligible and it is the second-level surrogate. Finally, the optimum design found by the surrogate is refined using space mapping technique to give an approximation of the location of the optimum design of the original problem. By taking advantages of both surrogate modeling and space mapping, the proposed approach can significantly improve the efficiency of the design process. The method is applied to optimize a double shield and a U-shaped double shield to show its efficiency.

This article analyzes the lightning transients in a commercial building with a grid like structure. The simulation is performed by using the partial element equivalent circuit method. Both the skin effect of the conductors and the nonlinear protection devices are taken into consideration. The induced voltage and the current sharing in the wiring system of both rising main circuit and secondary circuit are discussed. The influence of soil resistivity, lightning current waveform, different surge protection devices (SPDs) installations, and equipotential bonding are analyzed in this article. According to the simulation results, the soil resistivity can largely influence the potential of the conductor; however, it has a limited influence on the voltage between electric wires (potential difference). The SPDs installation arrangement and the equipotential bonding position in the building can greatly influence the lightning transients. The overvoltage and current can largely reduce if they are installed at a proper position. The suggestions provided in this article are constructive while designing the lightning protection system in buildings.

Lightning surge propagation on telecommunication towers is essential to lightning protection design. Analysis of very fast surges in a telecommunication tower requires a full-wave solution of Maxwell's equations. This paper proposes a full-wave time domain partial element equivalent circuit (PEEC) method considering the effect of ground to evaluate the surge currents and voltages on vertical structures. The PEEC of the formulation is provided by using the method of image. This method can take into account the attenuation of the lighting surges, and has the potential to be implemented as a new type of solution for general lightning surge analysis. The proposed method is validated numerically with the finite-difference time domain method, and is used to analyze the surge propagation on cables mounted on two typical grounded telecommunication towers. The simulation shows that both the location of cable installations and the type of towers have a significant influence on the lightning protection performance.

Different types of grounding systems are adopted in residential buildings due to various considerations such as location, regulation, etc. In order to reduce the potential electrical hazards, the appropriate grounding system should be selected according to the specific situation. The purpose of this study is to identify the suitable grounding system for urban villages or areas with similar situations. The discussions are based on a typical case that frequently happened in the urban village. According to our investigation, adopting TN-C-S system in urban villages is with a high risk of electric shock hazards due to the disadvantage of the system itself and the situation in the urban village. The reported case and analysis in this paper can provide a reference for selecting an appropriate grounding system.

This paper presents the data analysis of electrical fire incidents in Shenzhen, China. A detailed examination of 3192 electrical fire incidents from 2014 to 2018 is presented. Time distribution and spatial distribution of electrical fires in residential buildings are reported. The analysis of this study indicates that the prevention of electrical fires in urban villages is of great significance. Moreover, installing arc fault detection devices is necessary to reduce electrical fires. The results presented in this paper can be beneficial to policymakers for electrical fire prevention.

Along with the development of the smart grid, Shenzhen has constructed a grid adopting the “three-phase energy gateway + metering master station”. This paper comprehensively introduces the construction of the smart grid in Shenzhen. Based on the practical operation, both benefits and disadvantages of the current network are summarized. This work presents valuable experiences when constructing the smart grid and is useful for future smart grid development.

A grounding grid is essential to the lightning protection of power systems. This paper presents a modified partial element equivalent circuit method for predicting the transient behavior of the grounding grid. The frequency-dependent parameters of the grounding grid are obtained first by using the image method. Both modified nodal formulation and vector fitting techniques are applied to derive an extended equivalent network for time-domain simulation. In this method, the soil ionization effect is considered using a nonlinear resistance. The proposed method is verified with experimental results available in the literature. Finally, lightning transients in the grounding grid of a radio base station is presented. The ionization and propagation effects on grounding grid performance are discussed.

A thin-wire model of conductors with arbitrary cross sections for a finite-difference time-domain (FDTD) method is proposed for the study of lightning transients in electrical systems. The proposed thin-wire model considers both the frequency-dependent characteristics of the wires and the influences of the surrounding media. The model represents a wire using four FDTD cells with an equivalent side length and modified material parameters. A rational equivalent circuit is added at the center edge of the FDTD cells to represent the internal impedance of the wire. An analytical formula for determining the equivalent side length and the modified material parameters of the FDTD cells are also presented. The proposed formula gives a new prospect to build the thin-wire model in FDTD. In this model, the equivalent side length can be set arbitrarily and much larger than the original wire, which can greatly reduce the computation time. Meanwhile, the method can be extended to the thin-wire structure with arbitrary cross sections. The model is verified with various measurements. Finally, a practical grounding grid of a substation with external water supply is analyzed.

Density functional theory (DFT) calculations have been carried out to study the mechanism of N-alkylation of primary and secondary arylamines with aldehydes and ketones under the catalysis of the Lewis acid B(C6F5)3 using silanes. The B(C6F5)3-mediated reduction of organic substrates is usually reported under anhydrous conditions. It is noteworthy that Ingleson and co-workers have established that B(C6F5)3 could act as a water tolerant catalyst in N-alkylation of arylamines with aldehydes/ketones. Our DFT calculation results revealed that both Lewis acid B(C6F5)3 and water play important roles in the condensation of amine and aldehyde to generate an imine intermediate and in the subsequent reduction of imine to yield an amine product. In the condensation reaction, Bronsted acid B(C6F5)3-H2O acts as the effective catalyst to promote the proton transfer process. The activation free energy barrier is calculated to be 21.1 kcal/mol, which is 23.0 kcal/mol lower than that of the water-assisted condensation pat...