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A contribution to the engineering application of a proposed 500 kV fault current limiter (FCL) is presented. A new type of FCL composed of a highly coupled split reactor (HCSR) and fast switches is proposed. When the circuit breaker (CB) in series with the FCL in the 500 kV power system interrupts the limited fault current, the rate of rise of the recovery voltage (RRRV) reaches a value much higher than the rated value. Based on a simplified equivalent single‐phase circuit, the influence of the new FCL on the interruption procedure of the CB is simulated and discussed. The simulation results show that the high RRRV is caused by high‐frequency resonant oscillations between the HCSR and its parasite capacitance. Analysis indicates that when the reactance of the FCL is close to the short circuit reactance of the system, the RRRV will reach the highest value. To solve this issue, we proposed installing a shunt capacitor with the FCL. Simulation results showed that the RRRV under all fault modes could be restrained to below the rated value by introducing a certain shunt capacitor.

The drawn vacuum arc begins with a bridge column formed from the explosion of a liquid metal bridge after separating the contacts. The expansion process of the initial arc has an effect on arc motion or diffusion. In order to deeply study the influence of transverse magnetic field (TMF) and axial magnetic field (AMF) on the drawn arc characteristics in the initial expansion stage, in this article, arc ignition mode and appearance under two groups of contacts with different AMF and TMF components were experimentally studied. It was found that simultaneously reducing TMF and AMF components would end the expansion stage earlier, and the fluctuation of the arc column pressure during the expansion was larger. When TMF and AMF components were further reduced, the arc needs to take a longer time to extend across the slot gap due to insufficient Ampere force. When TMF was basically unchanged and AMF was reduced, the arc burned more intense, the diameter of the arc column was smaller, and the arc would merge earlier in multipoint ignition mode. The characteristics of arc voltage, pressure, and duration of expansion stage were analyzed, founding that the arc with a moderate TMF and AMF components had a smaller rising slope of arc voltage, a faster reducing speed of arc pressure, and a smaller range of the duration of expansion stage. In addition, the variation of magnetic field strength in different ignition modes and contact structures during the arc expansion stage was simulated to explain the mechanism of arc behavior.

Pregnant women’s influenza vaccination uptake was low, although being recommended as a priority. We conducted a cross-sectional questionnaire survey in China from June to July 2021. Hierarchical regression analysis and structural equation modeling were performed based on the extended theory of planned behavior, in which attitudes, subjective norms, perceived behavioral control, and intention each affect vaccine hesitancy; response efficacy, knowledge, vulnerability, and severity were added as extended dimensions; vaccination history played as a moderator. Totally, 1283 pregnant women participated in this study. The intention existed as a mediator between attitude [βindirect = 0.142 (95% confidence interval (CI): 0.084, 0.206), P < 0.001], subjective norms [βindirect = 0.568 (95%CI: 0.424, 0.754), P < 0.001], perceived behavioral control [βindirect = 0.070 (95%CI: 0.025, 0.118), P = 0.004] and vaccine hesitancy. Further, indirect effect differences between the two dimensions of attitude (P < 0.001), perceived behavioral control (P < 0.001), and subjective norms were each statistically significant. Vaccination history did not moderate the association between attitude (P = 0.679), subjective norms (P = 0.645), and hesitancy. The subjective norms dimension has a strong association with influenza vaccine hesitancy. Vaccination history was limited to reduce hesitancy.

Background Promoting vaccination and eliminating vaccine hesitancy are key measures for controlling vaccine-preventable diseases. Objective We aimed to understand the beliefs surrounding and drivers of vaccination behavior, and their relationships with and influence on vaccination intention and practices. Methods We conducted a web-based survey in 31 provinces in mainland China from May 24, 2021 to June 15, 2021, with questions pertaining to vaccination in 5 dimensions: attitude, subjective norms, perceived behavioral control, intention, and behavior. We performed hierarchical regression analysis and structural equation modeling based on the theory of planned behavior—in which, the variables attitude, subjective norms, and intention each affect the variable intention; the variable intention mediates the relationships of attitude and subjective norms with behavior, and the variable perceived behavioral control moderates the strength of this mediation—to test the validity of the theoretical framework. Results A total of 9924 participants, aged 18 to 59 years, were included in this study. Vaccination intention mediated the relationships of attitude and subjective norms with vaccination behavior. The indirect effect of attitude on vaccination behavior was 0.164 and that of subjective norms was 0.255, and the difference was statistically significant (P Conclusions Subjective norms have stronger positive influences on vaccination practices than attitudes. Perceived behavioral control, as a moderator, has a substitution relationship with attitudes and subjective norms and weakens their positive effects on vaccination behavior.

BACKGROUND Promoting vaccination and eliminating vaccine hesitancy are key measures for controlling vaccine-preventable diseases. OBJECTIVE We aimed to understand the beliefs surrounding and drivers of vaccination behavior, and their relationships with and influence on vaccination intention and practices. METHODS We conducted a web-based survey in 31 provinces in mainland China from May 24, 2021 to June 15, 2021, with questions pertaining to vaccination in 5 dimensions: attitude, subjective norms, perceived behavioral control, intention, and behavior. We performed hierarchical regression analysis and structural equation modeling based on the theory of planned behavior—in which, the variables attitude, subjective norms, and intention each affect the variable intention; the variable intention mediates the relationships of attitude and subjective norms with behavior, and the variable perceived behavioral control moderates the strength of this mediation—to test the validity of the theoretical framework. RESULTS A total of 9924 participants, aged 18 to 59 years, were included in this study. Vaccination intention mediated the relationships of attitude and subjective norms with vaccination behavior. The indirect effect of attitude on vaccination behavior was 0.164 and that of subjective norms was 0.255, and the difference was statistically significant (PPP=.006) with perceived behavioral control were significant. CONCLUSIONS Subjective norms have stronger positive influences on vaccination practices than attitudes. Perceived behavioral control, as a moderator, has a substitution relationship with attitudes and subjective norms and weakens their positive effects on vaccination behavior.

When the vacuum switch breaks a large current, the strong arc energy causes a large amount of metal vapor to be sputtered from the anode, and the anode is obviously a latex. Vigorous anode activity may reduce the strength of the medium recovery at the time of current zero crossing and re-ignite the arc, which prevents the current from successfully breaking. Therefore, anode activity has an important impact on the arc interruption. In this paper, the experimental research on the anode activity of the spiral slot transverse magnetic contact was carried out. The equipment used in the experiment and the process of the experiment are introduced. The contact morphology after arc ablation was compared by scanning electron microscopy analysis. The anode ablation was analyzed in combination with the spraying of inter-electrode droplets and the arc energy during arcing. The influence of contact structure, contact material and contact diameter on anode melting and ablation was discussed. The results show that the increase of chromium content is beneficial to reduce the ablation of anode contacts in a certain range. At the same time, the increase of contact diameter reduces the arc energy density, which is also beneficial to reduce ablation.

Severe anode activity may reduce the dielectric recovery strength of the interelectrode at zero current crossing and increase the possibility of arc reignition. On the other hand, arc motion between transverse magnetic field (TMF) contacts can avoid breaking failures caused by excessive ablation. Therefore, arc motion characteristics and the thermal change process in anode region have an important influence on the successful breaking of TMF contacts. In order to study the change process of anode activity during arc motion, based on the principle of conservation, an anode dynamic behavior model considering the deformation of anode surface under the action of TMF was established in this paper. In addition, heat transfer between arc and anode, movement of molten pool, deformation of free contact surface, and the complex physical processes in which the three were coupled to each other were involved in the model. The coexistence of gas, liquid and solid was considered in the model, and the fluid volume function was used to describe the anode surface morphology. Through the established model, the thermal variation of the anode region and the deformation of anode surface with development of arc motion were analyzed.

BACKGROUND It was reported that one in four parents were hesitant about vaccinating their children in China. Previous studies have revealed a declining trend in the vaccine willingness rate in China. There is a need to monitor the level of parental vaccine hesitancy toward routine childhood vaccination and hesitancy toward the COVID-19 vaccine during the ongoing COVID-19 pandemic. OBJECTIVE This study aims to assess changes in trends of parental attitudes toward routine childhood vaccines and COVID-19 vaccinations across different time periods in China. METHODS Three waves of cross-sectional surveys were conducted on parents residing in Wuxi City in Jiangsu Province, China from September to October 2020, February to March 2021, and May to June 2021. Participants were recruited from immunization clinics. Chi-square tests were used to compare the results of the three surveys, controlling for sociodemographic factors. Binary and multivariable logistic regression analysis was used to examine factors related to parental vaccine hesitancy and COVID-19 vaccine willingness. RESULTS Overall, 2881, 1038, and 1183 participants were included in the survey’s three waves. Using the Vaccine Hesitancy Scale, 7.8% (225/2881), 15.1% (157/1038), and 5.5% (65/1183) of parents showed hesitancy to childhood vaccination (PP CONCLUSIONS There has been an increasing acceptance of COVID-19 vaccination in Wuxi City, China. Effective interventions are needed to mitigate public concerns about vaccine safety.

This study evaluated different varicella vaccination strategies in Jiangsu province, China. A decision-tree Markov model was used to evaluate the cost effectiveness of various varicella vaccination strategies for children, including direct and selective vaccination (serotesting pre-vaccination). A cohort of one-year-old children was followed through 60 one-year Markov cycles. The parameter estimation was based on field work, the literature, and statistical yearbooks. We calculated the incremental cost-utility ratio (ICUR) using the saved quality-adjusted life year (QALY). One-way and probability sensitivity analyses were performed to assess uncertainty. Among 100,000 cohort members, one-dose and two-dose direct vaccination averted 8061 and 10,701 varicella cases, respectively, compared with no vaccination. Furthermore, compared with no vaccination, one-dose and two-dose direct vaccination saved one QALY at the ICUR of USD 21,401.33 and USD 35,420.81, respectively, at less than three times the per capita gross domestic product (USD 47,626.86) of Jiangsu. The ICURs of the one-dose and two-dose selective strategies versus no vaccination were USD 42,623.62 and USD 51,406.35 per QALY gained, respectively. The cost effectiveness results were most sensitive to the QALY loss of outpatients and vaccine prices. Thus, in Jiangsu, one-dose and two-dose direct varicella vaccination in children could be cost effective at the willingness to pay threshold of three times provincial GDP per capita from a societal perspective. The findings were sensitive to the vaccine price and health utility of varicella cases.

Vaccination against coronavirus disease 2019 (COVID-19) is paramount to curtailing the pandemic. However, the impact of the Non-Expanded Program on Immunization (non-EPI) and COVID-19 vaccine hesitancy on vaccine uptake among Chinese adults remain unclear. This study was an online survey performed in Eastern, Central, and Western China between February 2021 and March 2021 using proportional sampling (n = 7381). Adults aged ≥ 18 years were included, especially younger people (aged &lt, 65). Vaccine hesitancy was assessed using the 3C model and relative scales, logistic regression was used to explore the factors affecting vaccination uptake, structural equation modeling was used to evaluate the correlations between variables. Overall, 67.6% and 24.7% of adults reported vaccine hesitancy toward the non-EPI and COVID-19 vaccines, respectively. Participants (66.3%) reported taking the vaccine mainly based on recommendations from medical staff. Vaccine-hesitant participants (60.5%) reported a fear of side effects as the deciding factor in vaccine rejection. Vaccine hesitancy interacted negatively with confidence (β = −0.349, p &lt, 0.001) and convenience (β = −0.232, p &lt, 0.001), and positively with complacence (β = 0.838, p &lt, 0.001). Nonmedical personnel, adults who had previously received the influenza vaccine, and older people had lower vaccine hesitancy than their counterparts. Most Chinese adults have non-EPI but not COVID-19 vaccine hesitancy. Vaccine safety remains a concern.

The motion of arc between the transverse magnetic field (TMF) contacts gradually slows down and transits to the diffusion mode before the current zero crossing. The process of arc transition to diffusion mode seriously affects the contact surface ablation. However, the influence on vacuum arc transition to diffuse mode has not been deeply studied to date. In this paper, TMF contacts with different structures were investigated in a demountable vacuum chamber that contained a high-speed charge-coupled device video camera. It was found that current, arcing time, and axial magnetic field (AMF) components had significant effects on arc appearance, arc column diameter, and moment and current at which the arc transited to diffuse mode. The transition moment to diffuse mode exhibited a linear relationship with the peak current. The arc energy accumulated before diffuse mode would increase and the transition moment would be advanced when the peak current was increased. The range of the transition current to diffuse mode and small-current diffuse mode remain unchanged with peak current and arcing time. The arc column in the contacts with larger axial self-magnetic field had larger diameter while transiting to diffuse mode and also transited to the diffuse mode earlier and accumulated less energy during the transition.

The vacuum transverse magnetic field (TMF) contacts have the advantages of simple structure, short current path, and low cost. Arcing process and arc characteristics between the TMF contacts directly determine the temperature distribution and ablation of the contact surface, which are closely related to the breaking ability of the contacts. The axial magnetic field (AMF) component generated by the TMF contact structure also affects the arcing process. In this paper, five kinds of contacts with different starting positions of spiral slots were experimentally investigated in a demountable vacuum chamber. The arc appearance and the arc characteristics during different arcing stages and the surface utilization of the contacts were analyzed. The magnetic characteristics of arc in different stages were simulated. It was found that the arc with small AMF component has a large diameter and small range of motion. The arc with large AMF component might jet toward the outside of the interelectrode.

Great progress has been achieved in the development of fault current limiters (FCL) in recent years. However, there has been no domestic or overseas standard basis directly in terms of experimental verification. Short circuit testing of high-voltage FCL requires tremendous system capacities. Hence equivalent synthetic methods of testing should be considered. Due to the particularity of component parts in FCL, synthetic testing methods for circuit breakers may induce insulation stress in abnormal conditions. Based on the working principles of high-voltage FCL with high coupling split reactors, equivalent testing methods should be considered firstly, the paper conducts research and analysis on relevant domestic and overseas standards as well as lab capacities, and puts forward equivalent methods of short circuit testing. Then, testtag plans are formulated with actual working status. Lastly, system simulations on the feasibility of plans are carried out.

With the development of power system, the level of short circuit current is also increasing rapidly. As an effective method to limit short circuit current, fault current limiter (FCL) is more and more widely used. There are many kinds of fault current limiters according to their working principles. Compared with other types of fault current limiters, the fault current limiter based on high coupled split reactor (HCSR) has many advantages. Under normal operation condition, this type of fault current limiter shows very small leakage inductance. When short circuit fault occurs, it will change into current limiting reactor. The capacity of fault current limiter to withstand short-time withstand current and peak withstand current is an important evaluation index, and the reasonable equivalent test method is very important. In this paper, combined with the research of 500 kV and above voltage level AC fault current limiter, the test methods of short-time withstand current and peak withstand current of fault current limiter based on HCSR are comprehensively analyzed, so as to meet the requirements of short-time withstand current and peak withstand current test of fault current limiter based on HCSR.

Objectives: We aimed to (1) assess parental hesitancy about category A (Expanded Program on Immunization (EPI)) and B (non-EPI) vaccines, (2) assess parental willingness for COVID-19 and influenza vaccinations, and (3) explore the association of vaccination hesitancy of parents and healthcare workers (HCWs). Methods: The study was performed in Wuxi, eastern China between 21 September 2020 and 17 October 2020. Parents of children aged &lt, 18 years and HCWs were recruited from the selected immunization clinics. Vaccine hesitancy was assessed using the Strategic Advisory Group of Experts (SAGE) vaccine hesitancy survey (VHS) by summing the total score for 10 items (maximum 50 points). Results: A total of 3009 parents and 86 HCWs were included in the analysis. The category A VHS scores were significantly higher than the category B VHS scores (p = 0.000). Overall, 59.3% and 52.4% of parents reported willingness to avail COVID-19 and influenza vaccination for their children, respectively, 51.2% of the HCWs wanted to be vaccinated against COVID-19. Parental category B VHS scores were associated with HCW category B VHS scores (r = 0.928, p = 0.008). Conclusions: In China, parents are more hesitant about category B vaccines than category A vaccines. More than 40% of parents showed hesitancy and a refusal to use COVID-19 and influenza vaccines.

The transverse magnetic field (TMF) contacts can generate a transverse magnetic field driving the arc to rotate on the contact surface, which is beneficial to avoid severe ablation of contacts and improve the breaking performance. The contact structural parameters have an effect on the magnetic field distribution and vacuum arc characteristics. In this paper, the 3-D finite element models of spiral-type contacts with different number of slots were established, and the magnetic induction intensity distribution between contacts and the electromagnetic force of arc column were calculated. It was found that increasing the number of slots could effectively enlarge current density, and enhance the control of arc motion, but it would continually cause an arc motion to cross slots. Therefore, it was necessary to comprehensively consider the influence of the two aspects in the design of contact structure. The inductor-capacitor (LC) oscillation circuit was used to establish the experimental system. The vacuum arc appearances of 3-slot contacts and 4-slot contact were recorded by high-speed video camera, and the comparative analysis of vacuum arc and arc voltage characteristics were carried out. It could be observed that the 4-slot contacts had a higher concentration degree of arc column and a longer duration of arc voltage noise during the arc motion stage, in the meanwhile, the arc motion was more obvious.

Objectives This study aimed to examine childhood vaccination delay, explore the association between vaccination delay and parental vaccine hesitancy, and assess childhood vaccination delays during the coronavirus disease (COVID)-19 pandemic in China. Methods This cross-sectional survey was conducted in Wuxi City. Participants were recruited from local vaccination clinics. Questionnaires were used to collect information about socio-demographics, vaccine hesitancy, and immunization clinic evaluations. Vaccination records were obtained from the Jiangsu Information Management System of Vaccination Cases. Results Overall, 2728 participants were included. The coverage for seven category A vaccines (Expanded Program on Immunization (EPI)) was more than 95% at 24 months. The proportion of children vaccinated in a timely manner was the highest for the first dose of the hepatitis B vaccine (91.6%) and the lowest for the Bacillus-Calmette-Guerin vaccine (44.6%). More than 50% of the planned vaccinations were delayed in February and March 2020. The Vaccine Hesitancy Scale scores were not associated with vaccination delay (P=0.842). Children's vaccination delays were negatively associated with parents who reported convenient access to clinics and satisfaction with immunization services (P=0.020, P=0.045). Conclusions EPI is highly successful in China. Despite vaccination delays due to the COVID-19 pandemic, coverage was recovered after lockdown restrictions were eased.

In the initial separation period of anode and cathode contacts, one or more vacuum arcs are generated in contact gap. This paper analyzed different arc ignition modes between Wan-Type transverse magnetic field (TMF) contacts. The three-dimensional finite element simulation models of contacts were established, and the magnetic field distribution and electromagnetic force applied to two arc columns and a single arc column with different arc column intervals were simulated and calculated. It could be found that, under the influence of arc self-generated magnetic field, the electromagnetic force direction of two arc columns had a certain degree of deviation, and the larger arc column interval, the weaker interaction between arc columns. The inductor-capacitor (L-C) oscillating circuit and demountable vacuum chamber were used to establish the experimental system, and the arc appearances were recorded by the high-speed camera to analyze the vacuum arc appearances and expanding characteristics under single-point arc ignition mode, two-point arc ignition mode and three-point arc ignition mode. The influence of contact diameter was also studied. The results showed that the multi-point arc ignition mode was more likely to be formed under a larger breaking current, in addition, with the increase of breaking current, the first two-point arc ignition mode of contacts with smaller diameter appeared earlier.

Background: Vaccine hesitancy is one of the top ten health threats. We aimed to (1) assess parental Category B vaccines hesitancy and associated sociodemographic factors in China, and (2) explore the association between attitude toward vaccines and self-reported hesitant behaviour.Methods: A cross-sectional study was performed through a web-based anonymous online questionnaire survey between 9 February 2021 and 7 April 2021. Chinese parents aged ≥ 18 years who had one child aged < 6 years were included to assess vaccine hesitancy using the vaccine-hesitancy scale (VHS). A structural equation model was used to determine relationships between variables.Results: Of 2952 Chinese parents included in the analysis, 17.5% were highly hesitant in using Category B vaccines. Parents who were younger, less educated, engaged in health-related occupations, and had been vaccinated against influenza in the past year were more hesitant when vaccinating their children (P < 0.001). VHS score accuracy to identify vaccine-hesitant behaviour was acceptable, and the optimal cut-off was 37.50 (with 61.96% parental vaccine hesitancy). Parents who lack confidence or believe vaccines were risk were more likely to show vaccine hesitant behaviour (P

The severity of the contact surface ablation determines the breaking capacity of the vacuum circuit breaker, and the interaction between the arc root and the electrode is the main cause of the contact surface ablation. The characteristics of the arc root determine the magnitude of the electromagnetic force received by the arc during the movement stage as well as the shape and speed of the arc movement. It will eventually affect the temperature of the contact surface and the ablation situation. This paper studied the arc root characteristics of high-current constricted vacuum arcs between the iron-core cup-shaped transverse magnetic field contacts and put forward the idea of using the ratio of cathode and anode arc root areas to quantitatively analyze the concentration of vacuum arc. The research on the arc root characteristics of the vacuum arc can help to improve the arc characteristics and arcing mechanism, and the proposition of the ratio can provide a new method for the study of constricted arc. This can provide a basis for improving the arc extinction performance of the switch, reducing the ablation of the contact material, and improving the contact life.

Based on the modeling of the structural parameters of the 550kV high coupled split reactor, the electromagnetic coupling method are used to establish the 3D mechanical stress and thermal stress calculation model of the high coupled split reactor, and the mechanical stress and thermal stress distribution characteristics of the overall and encapsulation of the high coupled split reactors are studied. The simulation results of this paper show that: the direction of the electric power in the single arm current limiting is mainly distributed axially symmetrically outward, and symmetrically about the middle of the vertical height, the radial force from the inside to outer encapsulation is gradually reduced, and the outermost side has a weaker contrat tendency. In general, each encapsulation has an outward expansion tendency. At the same time, the temperature distribution of the high coupled split reactor shows that the upper region is higher than the lower region, and the intermediate encapsulation is higher than the encapsulation trend of the two sides. The highest hot spot temperature is 10-cated in the upper region of the middle of the high coupled split reactor. The research results provide a theoretical basis for the design and optimization of the 550kV high coupled split reactor test scheme.

The phenomenon of 500 kV line short-circuit urrent exceeding the protection scope of circuit breaker is seriously threatening the safety of power grid, and installing a suitable fault current limiter is an effective method to deal with such problem. 550 kV high coupled split reactor studied in this paper is an important component of 500kV fault current limiter that is desighed with new technology. It has the functions of withstanding and limiting short-circuit current, and has the advantages of high flexibility, easy maintenance and low loss. However, at present, there is a lack of relevant literature and standards to guide this type of equipment for the evaluation of mechanical and thermal stress under actual conditions. This paper studied the actual working conditions of 550kV high coupled split reactor, analyzed its current characteristics, and on this basis, performed steady-state temperature field simulation analysis at rated continuous current and stress calculation during short circuit, and proposed a scheme for equivalent test using a small prototype in the actual conditions of the laboratory. This paper is beneficial to the design and testing of such equipment in the future.

The structure of the arc chamber has a great influence on gas flow during the interrupting process, which is an important technical index to determine the performance of the high voltage circuit breaker. In this paper, to calculate the flow field of the arc chamber, the computational fluid dynamics calculation software Fluent was used. The pressure and velocity were acquired by calculating the flow field of the simulation model during the interruption period. Through analyzing the calculation results, the influence of each parameter on the interrupting ability of the circuit breaker was studied. To research the influence of structure sizes on the flow field, the arc chambers with different nozzle and cylinder were calculated. Based on the findings, the structure size of the arc chamber was designed finally.

The transverse magnetic field (TMF) contact has the advantages of small loop resistance, simple structure, and strong breaking ability. In order to make the arc mode more stable and reduce the metal droplets splashed in the radial direction, this paper proposed an improved cup-shaped TMF contact. The simulation of the magnetic field showed that this contact structure could effectively enhance the axial magnetic flux intensity, especially in the small gap distance. Therefore, the arc could keep in a more diffuse mode in the ignition and expansion stages. The experimental results showed that the improved cup-shaped TMF contact had more stable arc mode and less arc droplets compared with the traditional cup-shaped TMF contact. The arc characteristics of the improved TMF contact meet our anticipated goals. Based on these experimental results, a further research for contact parameters optimization is still in work.

Transverse magnetic field (TMF) contacts can prevent local overheat by creating a TMF and driving the vacuum arc to rotate around the contact periphery, thus improving the breaking performance of vacuum circuit breaker. The arcing behavior and the transition between arcing stages have great influence on the heat distribution on the contact surfaces, and they will finally affect the interruption at current zero. In this paper, a demountable vacuum chamber was used to investigate the arc behavior between two kinds of TMF contacts. A digital high-speed camera was used to record the arcing process. By combining the arcing appearance with arc voltage waveform, the arcing process was divided into four stages: initial expansion stage, arc instability stage, arc motion stage, and diffuse stage. The voltage characteristic and arc appearance of each stage were summarized and analyzed, and the transition condition between different stages was acquired. Moreover, the influence of current level and contact parameters on the duration and transition moment of each stage was also studied. The experimental results indicate that the initial stage is influenced by the arc ignition mode, whereas the arc motion and diffuse stage are significantly affected by the current level, contact type, and diameters. With the increase of peak current level, the duration of arc motion stage will increase, while the transition moment from arc motion to diffuse stage will move toward current zero.

Sulfur hexafluoride (SF6) has excellent insulating and arc quenching properties, but it has strong greenhouse effect which is 23900 times of CO 2 . Nitrogen (N2) is an environmental-friendly gas with good insulation performance and is developed to use in gas insulated equipment in recent years. In this paper, the effect of humidity and purity on N 2 insulated switchgear was researched. A 40.5 kV N 2 insulated switchgear was taken as the test object. Short-duration power-frequency withstand voltage test and lightning impulse voltage test were carried out under different gas purity and humidity. The test results showed that N2 mixed with 20% O 2 can pass both tests. N 2 containing 650 ppm, 1200 ppm and 2380 ppm water can pass both tests. While the water content increased to 12700 ppm, the switchgear cannot pass the test. From the aspects of ionization energy and electronegativity, the test results were analyzed. The results can provide guidance and basis for the maintenance and operation of N 2 insulated switchgears.