Experiment study on a spiral-cup shaped TMF contact

In this paper, combined with the characteristics of spiral-shaped transverse magnetic field (TMF) contacts and cup-shaped TMF contacts, a new structure of spiral-cup shaped contacts was designed. Firstly, experiments were carried out on two kinds of TMF contacts – the traditional cup shaped contacts and the new spiral-cup shaped contacts. Arc behaviors were recorded and the arc motion were studied. The experimental results indicated that the arc motion between new contacts was better than that between the traditional cup-shaped contacts. Here, we paid particular attention to the arc characteristics between spiral-cup shaped TMF contacts. The duration and threshold current of different stages with different tested currents were discussed, and the arc characteristics during arc motion stage was analyzed. Moreover, electromagnetic field simulation was conducted on above two kinds of TMF contacts, and the distributions of magnetic field and the electromagnetic forces acted on arc were compared. According to the simulation results, some experimental phenomena were explained theoretically. In addition, the spiral-cup shaped structure proposed here makes it possible to research on arc movement mechanism without considering the complex mechanism of arc stepping over slots

Modeling and numerical simulation of anode activity and arc motion in a transverse magnetic field

Vacuum interrupters based on transverse magnetic field contacts now are widely used in medium voltage circuit breakers. The arc motion under the transverse magnetic field (TMF) plays a decisive role in the interruption. In this paper, we focus on the movement of vacuum arc driven by TMF and anode thermal process during the arcing. Then, based on the principle of conservation, a transient two-dimensional anode activity model (subjected to TMF constricted arc) is established. The state change of material, evaporation from contacts and motion of molten pool are also considered in our model. By considering the arc motion in the anode activity model, the transient anode thermal process and the movement of constrict arc under TMF are studied, respectively. The simulation predicted that average speed of arc is not higher than 200m/s. In the simulation, the anode surface is completely melted near the current peak with 200 μm molten layer. In addition, the influence of movement of molten pool on the arc speed is analyzed, finding that the movement of the bath accelerates arc speed, but weakens the surface melting at the same time

Synthetic test circuit with two‐level voltage source for HVDC circuit breakers

Abstract In order to ensure the reliable interruption of high voltage direct current circuit breaker (HVDC CB), the breaking test of HVDC CB plays an important role in its performance verification. In this paper, the interruption process of the HVDC CB is analyzed, and the equivalent requirements for the breaking test of HVDC CB are summarized. In the breaking test of high voltage and high current, the transient interruption voltage (TIV) duration is short, which leads to insufficient voltage stress. A new synthetic test circuit for testing the interruption performance of HVDC CBs is proposed, which can solve the problem of insufficient TIV duration caused by insufficient test capacity. Subsequently, the working principle of the test circuit is introduced in detail and the design method of the circuit parameters is given. The short‐circuit current breaking test simulation of HVDC CB is carried out. The simulation results fit most well with the results of actual test cases, which verifies the universality of this test method. Finally, a test platform is built to verify the principle of the test circuit. TIV rose to 2.5 kV compared to the predetermined system voltage of 1.67 kV during the test, which means that the key stress provided by the test circuit can meet the expected requirements

Perceptions about respiratory syncytial virus (RSV) and attitudes toward the RSV vaccine among the general public in China: A cross-sectional survey

ABSTRACTOur study aims to assess the public’s perceptions of respiratory syncytial virus (RSV) and attitudes toward the RSV vaccine and to identify associated factors in China. A nationwide cross-sectional survey conducted using an online platform between August 16 and September 14, 2023. Questions related to socio-demographics, awareness, knowledge, perceptions of susceptibility and severity of RSV, and attitudes toward the RSV vaccine were included in the questionnaire. We used the chi-square test and logistic regression model to explore the associated factors. Overall, 2133 individuals were included in this study. Nearly a quarter of participants (24.3%) indicated that they had never heard of RSV. The proportion of individuals aged over 50 years reporting never having heard of RSV (36.5%) and having a low knowledge level of RSV (55.3%) was significantly higher that of other younger age groups. More than half of individuals (55.7%) exhibited low level of perceptions of susceptibility concerning RSV infection. A total of 68.4% of the participants expressed willingness to receive the RSV vaccine. Younger age was positively associated with a higher willingness to be vaccinated. The most frequent reason for declining the vaccine was “Concern about vaccine’s safety or side effects.” About 60% of individuals considered a price of RSV vaccine below 200 CNY (28 USD) as acceptable. The awareness and perceived susceptibility to RSV infection were limited to the Chinese public. It is necessary to take measures to address the low awareness and knowledge of RSV and acceptability of the RSV vaccine among older adults

Perceptions and acceptability of HPV vaccination among parents of female adolescents 9–14 in China: A cross-sectional survey based on the theory of planned behavior

HPV vaccine uptake remains low in China, especially among girls. Recently, China has initiated a pilot program on HPV immunization for girls 9–14. From November to December 2021, a cross-sectional study was conducted among parents of girls 9–14 in China through a web-based anonymous online questionnaire survey. Descriptive epidemiological analysis was used to analyze parental acceptability. Hierarchical regression analysis and structural equation modeling were to determine associated factors. A total of 5623 participants were included in the analysis. 21.2% girls had received HPV vaccine, and 94.3% parents intended to receive vaccination for their daughters, the Kappa values between them was −0.016. 31.9% of vaccinated mothers had received HPV vaccine for their daughters, vaccination history had a positive impact on behavior (β = 0.048). Attitude (β = 0.186), subjective norms (β = 0.148) and perceived behavioral control (β = 0.648) had a positive impact on intention. Vaccination intention mediated the relationships between attitude (β = 0.044), subjective norms (β = 0.035), and perceived behavioral control (β = 0.154) with behavior. There is a gap between vaccination intention and behavior in parents of girls 9–14. Perceived behavior control had a strong association on HPV vaccination behavior