Super large capacity converter transformer

Nowadays, the huge demand for long-distance UHVDC transportation prompts research on the super large capacity converter transformer. Especially in China, UHVDC projects are widely built and put into use. This article reviews the history of converter transformer research and introduces details in the design of the converter transformer. The recent advances in the fundamental study of converter transformers such as partial discharge, space charge, and material performance test are also introduced in the article. In the end, this article summarizes the application status of the converter transformer in China and looks forward to its future prospects

How Individual Characters Affect the Ex ante Moral Hazard of Basic Medical Insurance: Evidence from China

How individual characters affect the ex ante moral hazard of basic medical insurance still remain academically debatable. This paper based on divergent individual characters of insurers to analyze the roles of basic health insurance on the ex ante moral hazard. It found health level, marital status, income level and age are the key individual factors affecting ex ante moral hazard of basic health insurance. But the roles of rural-urban difference and gender are not obvious. It gives supplementary explanations to the medical service expenditure, waste of medical resources and other issues, and also put forward the corresponding policy recommendations

Greenway Planning of Guangdong Province

Guangdong Province is located in the southernmost region of mainland China with a total area of 180,000 square kilometers. The GDP ranks first in China, and the economic aggregate accounts for 1/8 of China’s total. As the economic development continues, the fragmentation of ecological land is becoming more dangerous. To solve this problem, the local government organized the master planning of environmental protection. The provincial greenway planning (also called ecological corridor) proposed in this paper is an essential part of it. The total length of planned greenways in Guangdong Province is 2,836 kilometers, and its primary function is biodiversity conservation. In the master planning of environmental protection, the planning of the ecological red line has already identified ecological patches. By constructing the provincial backbone greenway to connect ecological patches and form an ecological network, it can guarantee the ecological area of an economic priority development zone like Guangdong Province to provide sustainable ecosystem services. In this paper, the traditional Minimum Cumulative Resistance method (MCR) has been optimized based on graph theory, by using the betweenness of the edge (route or corridor) and selecting the least connected subgraph with the highest betweenness of the potential greenway by irreplaceable conditions to determine the irreplaceable backbone route and key strategic points. Under the premise of ensuring connectivity, the goal of planning the least number of greenways, the smallest footprint, and the constant value of ecosystem service is achieved. In this method, the backbone structure of the eco-network that maintains ecological security is established, nodes are found which are important hub locations in the eco-network but poor ecological conditions, and greenway route redundancy problem generated by the MCR method was solved, land resources and funds are saved, the guidance and control functions of the provincial greenway system are realized. The plan has been reviewed by the local government and entered the implementation phase

Electrical Property of Polypropylene Toughened by β Nucleating Agent

High-performance polymer insulating material is a crucial knob for developing HVDC power cables. However, the production process of traditional cross-linked polyethylene, especially degassing, is complicated. The space charge accumulation could render severe electric field distortion under high temperatures and electrical stresses, detrimental to the insulation reliability. As a potential alternative, polypropylene (PP) has excellent properties and is environmentally friendly. However, crucial challenges for the PP application include brittleness deficiency at low temperatures and space charge problems caused by toughened PP composites. In recent years, the β nucleating agent (β-NA) has emerged as an effective additive to improve mechanical and electrical properties due to the introduction of the β-crystal form. Herein, PP/β-NA with different contents and self-assembled β-NA were subsequently prepared, respectively. The melting and crystallization behaviors, crystalline structure, and electrical properties were systematically investigated, and the influence on the space charge characteristics of PP/β-NA composites was explored. We aim to summarize the β-crystal form regulation strategies for advanced PP materials and how they perform, point out the critical characteristic parameters to improve the target performance, and offer suggestions for the rational design for future HVDC cable engineering

Incorporation of Extranodal Metastasis of Gastric Carcinoma into the 7th Edition UICC TNM Staging System

BACKGROUND: To assess the clinical significance and prognostic impact of extranodal metastasis (EM) in gastric carcinoma and establish an optimal classification in the staging system. METHODOLOGY/PRINCIPAL FINDINGS: A total of 1343 patients with gastric carcinoma who underwent surgical resection were recruited to determine the frequency and prognostic significance of EMs. EMs were divided into two groups (EM1 and EM2) and then incorporated into the 7(th) edition UICC TNM staging system. EMs was detected in 179 (13.3%) of 1343 patients who underwent radical resection. Multivariate analysis identified EMs as an independent prognostic factor (HR = 1.412, 95%CI = 1.151-1.731, P<0.001). After curative operation, the overall survival rate were worse in patients with ≥3 cases of EM (EM2) than those with the number of 1 and 2 cases (EM1) (P<0.001). Survival of patients with EM1 was found almost comparable to that of N3 stage (P = 0.437). Survival of patients with EM2 showed similar to that of stage IV patients (P = 0.896). By using the linear trend X(2), likelihood ratio X(2), and Akaike information criterion (AIC) test, EM1 treated as N3 stage and EM2 treated as M1 stage performed higher linear trend X(2) scores, likelihood ratio X(2) scores, and lower AIC value than the 7(th) edition UICC TNM staging system, which represented the optimum prognostic stratification, together with better homogeneity, discriminatory ability, and monotonicity of gradients. CONCLUSIONS/SIGNIFICANCE: EMs might be classified based on their number and prognostic information and should incorporate into the TNM staging system

Microwave-assisted aqueous two-phase extraction of alkaloids from Radix Sophorae Tonkinensis with ethanol/Na2HPO4 system: process optimization, composition identification and quantification analysis

A rapid method for simultaneous extraction and separation of multiple alkaloids from Radix Sophorae Tonkinensis (RST) was developed by microwave-assisted aqueous two-phase extraction (MAATPE) using the aqueous two-phase extraction system (ATPS) of ethanol/Na2HPO4 as the extraction solvent. The effects of key factors on extraction yield were investigated by utilizing single-factor experiment coupled to response surface methodology (RSM). The regression model by RSM was significant (p < 0.0001) and adequate for prediction of process efficacy, the optimized conditions were successfully validated by the parallel experiments with the yield very close to the predicted value. The optimum conditions were summarized as follows: the phase ratio of 2.60 for the ATPS, the particle size of 100 mesh, the liquid-to-material ratio of 75:1, the extraction temperature of 90 °C and the extraction time of 5 min, respectively. In MAATPE process, alkaloids were extracted preferentially from RST in the top phase with a higher yield and shorter extraction time than those of heating reflux extraction (HRE) and ultrasonic-assisted extraction (UAE). Nine alkaloids extracted were identified and quantified by high-resolution ultra-performance liquid chromatography-quadrupole-orbitrap mass spectrometry (UPLC-Q-Orbitrap/MS) and HPLC with UV detection. The contents of matrine, sophocarpine, oxymatrin, sophoranol, oxysophocarpine, 5α-hydroxysophocarpine, sophoridine, cytisine and N-methylcytisine in RST were quantified in range of 0.493–10.284 mg/g with recoveries of 90.26–106.3% and RSD’s of 0.8–2.1%, respectively. Moreover, the MAATPE mechanism was explored using the different extraction systems in combination of scanning electron microscopy (SEM) morphological studies. Significant differences in extraction yield and cell rupture exhibited that the addition of the salt in the ethanol-water mixture not only improved the thermal and demixing effects, but also accelerated the mass transfer and biphasic extraction processes. MAATPE integrated the advantages of microwave-assisted extraction (MAE) and aqueous two-phase extraction (ATPE) was proved as a green, efficient and promising alternative to extraction of alkaloids from RST

New Improvement of Labor Accounting in the Sharing Economy

The investigation of labor is a key aspect of population research, and labor accounting, as its foundation, is an important means to judge the degree of economic development and monitor the changes of the labor market, having always been a focus of scholarly research. At present, the sharing economy is on the rise worldwide and influences labor accounting. In this paper, starting from the context of the sharing economy and the current situation of labor accounting, several important aspects of labor accounting will be discussed. In the context of the sharing economy, household subsistence service production is to be included in the production accounting boundary, which is the root of the changes in labor accounting. On this basis, the following findings are drawn. (1) The scope of accounting for employment should be expanded, which puts higher demands on the labor accounting method. (2) Working time should be remeasured, especially indicators based on pay time. (3) Finally, the design of indicators in labor underutilization also requires the formation of new ideas, especially unemployment should be redefined. Finally, in view of the current status of labor accounting in China, policy suggestions for future improvement under the sharing economy are put forward

Pattern Recognition of Development Stage of Creepage Discharge of Oil–Paper Insulation under AC–DC Combined Voltage Based on OS-ELM

The recognition of the creepage discharge development process of oil–paper insulation under AC–DC combined voltage is the basis for fault monitoring and diagnosis of converter transformers; however, only a few related studies are available. In this study, the AC–DC combined voltage with a ratio of 1:1 was used to develop a recognition method for the creepage discharge development process of an oil–paper insulation under a cylinder–plate electrode structure. First, the pulse current method was used to collect the discharge signals in the creepage discharge development process. Then, 24 characteristic parameters were extracted from four types of creepage discharge characteristic spectra after dimensionality reduction. Finally, based on the online sequential extreme learning machine (OS-ELM) algorithm, these characteristic parameters were used to recognize the development stage of the creepage discharge of the oil–paper insulation. The results showed that when the size of the sample training set used in the OS-ELM algorithm is close to the number of hidden layer neurons, a high recognition accuracy can be obtained, and the type of activation function has little influence on the recognition accuracy. Four stages of the creepage discharge development process were recognized using the OS-ELM algorithm; the trend was the same as that of the characteristic parameters of the entire creepage discharge development process. The recognition accuracy was 91.4%. The algorithm has a high computing speed and high accuracy and can train data in batches. Therefore, it can be widely used in the field of online monitoring and evaluation of electrical equipment status

Dramatically enhanced electrical breakdown strength in cellulose nanopaper

Electrical breakdown behaviors of nanopaper prepared from nanofibrillated cellulose (NFC) were investigated. Compared to conventional insulating paper made from micro softwood fibers, nanopaper has a dramatically enhanced breakdown strength. Breakdown field of nanopaper is 67.7 kV/mm, whereas that of conventional paper is only 20 kV/mm. Air voids in the surface of conventional paper are observed by scanning electron microscope (SEM). Further analyses using mercury intrusion show that pore diameter of conventional paper is around 1.7 μm, while that of nanopaper is below 3 nm. Specific pore size of nanopaper is determined to be approximately 2.8 nm by the gas adsorption technique. In addition, theoretical breakdown strengths of nanopaper and conventional paper are also calculated to evaluate the effect of pore size. It turns out that theoretical values agree well with experimental data, indicating that the improved strength in nanopaper is mainly attributed to the decreased pore size. Due to its outstanding breakdown strength, this study indicates the suitability of nanopaper for electrical insulation in ultra-high voltage convert transformers and other electrical devices

A Combined Electro-Thermal Breakdown Model for Oil-Impregnated Paper

The breakdown property of oil-impregnated paper is a key factor for converter transformer design and operation, but it is not well understood. In this paper, breakdown voltages of oil-impregnated paper were measured at different temperatures. The results showed that with the increase of temperature, electrical, electro-thermal and thermal breakdown occurred successively. An electro-thermal breakdown model was proposed based on the heat equilibrium and space charge transport, and negative differential mobility was introduced to the model. It was shown that carrier mobility determined whether it was electrical or thermal breakdown, and the model can effectively explain the temperature-dependent breakdown