Effect of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy

The effects of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy extruded bar were investigated through various analyses,including electrical conductivity,mechanical properties,local corrosion properties,and slow strain rate tensile stress corrosion tests.Microstructure characterization techniques such as metallographic microscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM)were also employed.The results indicate that the tensile strength of the alloy produced by T6I6 aging is similar to that produced by T6I4 aging,and it even exceeds 700 MPa.Furthermore,the yield strength increases by 52.7 MPa,reaching 654.8 MPa after T6I6 aging treatment.The maximum depths of intergranular corrosion(IGC)and exfoliation corrosion(EXCO)decrease from 116.3 and 468.5μm to 89.5 and 324.3μm,respectively.The stress corrosion factor also decreases from 2.1%to 1.6%.These findings suggest that the alloy treated with T6I6 aging exhibits both high strength and excellent stress corrosion cracking resistance.Similarly,when the alloy is treated with T6I4,T6I6 and T6I7 aging,the sizes of grain boundary precipitates(GBPs)are found to be 5.2,18.4,and 32.8 nm,respectively.The sizes of matrix precipitates are 4.8,5.7 and 15.7 nm,respectively.The atomic fractions of Zn in GBPs are 9.92 at.%,8.23 at.%and 6.87 at.%,respectively,while the atomic fractions of Mg are 12.66 at.%,8.43 at.%and 7.00 at.%,respectively.Additionally,the atomic fractions of Cu are 1.83 at.%,2.47 at.%and 3.41 at.%,respectively.

Influence of Interrupted Childhood Biographies on Health Development: Evaluation of the Scientific Literature on the Example of Being Taken into Care*

Background: An interrupted family history, as is the case after taking someone into care, can complicate collecting family anamnesis data. In addition, the interrupted family history itself could be considered part of a person’s risk profile. Aim and methods: Literature analysis was conducted to examine whether there are scientific studies on health development after placement in out-of-home-care in order to recognise any existing medical characteristics that may be relevant for internal medical care. Results: There are few scientific publications on the health development of people after being placed in out-of-home-care. Direct reactions to the stress of being taken into custody include nausea and fever. However, effects that go beyond the acute situation and last into adulthood have also been described, such as AD(H)D, asthma, diabetes, cancer, hypertension and cardiovascular diseases (myocardial infarction, stroke), epilepsy and increased overall mortality in adulthood. Studies show that not only previous experience but also the stress of being taken into care is triggers for this. Conclusion: Information about a previous institutionalisation can hence be important for internal medical practice. The available scientific literature shows heterogeneous study methodology and no group of people with experience of out-of-home-placement has yet been scientifically accompanied for a long time period. Further studies on this could help to better weigh up the consequences of omitting and conducting an intervention for child/youth protection as well as to improve the medical care for this group of people.

Feasibility and clinical benefits of the double-ProGlide technique for hemostasis after cryoballoon atrial fibrillation ablation with uninterrupted oral anticoagulants

OBJECTIVE To access the efficacy and safety of the double-ProGlide technique for the femoral vein access-site closure in cryoballoon ablation with uninterrupted oral anticoagulants(OAC),and its impact on the electrophysiology laboratory time as well as hospital stay after the procedure in this observational study.METHODS Patients with atrial fibrillation undergoing cryoballoon ablation with uninterrupted OAC at Department of Cardiology,Beijing Anzhen Hospital,Capital Medical University,Beijing,China from May 2019 to May 2021 were enrolled in this study.From October 2020,double-ProGlide technique was consistently used for hemostasis(ProGlide group),and before that conventional manual compression was utilized(manual compression group).The occurrence of vascular and groin complications was accessed during the hospital stay and until the three-month follow-up.RESULTS A total of 140 participants(69.30%of male,mean age:59.21±10.29 years)were evaluated,70 participants being in each group.Immediate hemostasis was achieved in all the patients with ProGlide closure.No major vascular complications were found in the ProGlide group while two major vascular complications were occurred in the manual compression group.The incidence of any groin complication was obviously higher in subjects with manual compression than patients with ProGlide devices(15.71%vs.2.86%,P=0.009).In addition,compared with the manual compression group,the ProGlide group was associated with significantly shorter total time in the electrophysiology laboratory[112.0(93.3–128.8)min vs.123.5(107.3–158.3)min,P=0.006],time from sheath removal until venous site hemostasis[3.8(3.4–4.2)min vs.8.0(7.6–8.5)min,P<0.001],bed rest time[8.0(7.6–8.0)h vs.14.1(12.0–17.6)h,P<0.001]and hospital stay after the procedure[13.8(12.5–17.8)h vs.38.0(21.5–41.0)h,P<0.001].CONCLUSIONS Utilization of the double-ProGlide technique for hemostasis after cryoballoon ablation with uninterrupted OAC is feasible and safe,which has the clinical benefit in reducing the total electrophysiology laboratory time and the hospital stay length after the procedure.

Interrupted Time Series Analysis of Military and Civilian Regimes in Nigeria: A Statistical Evidence from Gross Domestic Product (GDP)

Governments influence the economy by changing the level and types of taxes, the extent and composition of spending, and the degree and form of borrowing. Governments directly and indirectly influence the way resources are used in the economy. Higher taxes, fees, and greater regulations can stymie businesses or entire industries and the resulting impact is reflected on the country’s economy status (strong or weak). The growth rate of GDP is often used as an indicator of the general health of the economy. In broad terms, an increase in real GDP is interpreted as a sign that the economy is doing well. So it is important to study and pay more attention to country’s GDP growth rate. In this paper, an intervention analysis approach was applied to Nigeria GDP data in order to evaluate the performances of military and civilian rules in the country. Data on Nigeria GDP were collected and subjected to interrupted (intervention) time series model. Based on the Alkaike Information Criterion (AIC), Bayesian Information Criterion (BIC) and sigma2 values, the interrupted time series model ARIMA (1, 1, 0) with exogenous variables (per capita per capita GDP, intervention, year and yearAfter) was identified as the best model amongst other competing models. It was observed that the intervention (civilian rule) was significant at the 10% level of significance in increasing the Nigeria GDP by 10B US$ on the average since 2005 till 2021 while controlling for the effects of other determinants. Also, the ARIMA (1, 1, 0) forecasts indicate that the Nigeria GDP will continue increasing during the civilian rule. As a result, changing from military rule to civilian rule in Nigeria significantly increased the GDP of the country.

Interrupted Time Series Analysis of Military and Civilian Regimes in Nigeria: A Statistical Evidence from Gross Domestic Product (GDP)

Governments influence the economy by changing the level and types of taxes, the extent and composition of spending, and the degree and form of borrowing. Governments directly and indirectly influence the way resources are used in the economy. Higher taxes, fees, and greater regulations can stymie businesses or entire industries and the resulting impact is reflected on the country’s economy status (strong or weak). The growth rate of GDP is often used as an indicator of the general health of the economy. In broad terms, an increase in real GDP is interpreted as a sign that the economy is doing well. So it is important to study and pay more attention to country’s GDP growth rate. In this paper, an intervention analysis approach was applied to Nigeria GDP data in order to evaluate the performances of military and civilian rules in the country. Data on Nigeria GDP were collected and subjected to interrupted (intervention) time series model. Based on the Alkaike Information Criterion (AIC), Bayesian Information Criterion (BIC) and sigma2 values, the interrupted time series model ARIMA (1, 1, 0) with exogenous variables (per capita per capita GDP, intervention, year and yearAfter) was identified as the best model amongst other competing models. It was observed that the intervention (civilian rule) was significant at the 10% level of significance in increasing the Nigeria GDP by 10B US$ on the average since 2005 till 2021 while controlling for the effects of other determinants. Also, the ARIMA (1, 1, 0) forecasts indicate that the Nigeria GDP will continue increasing during the civilian rule. As a result, changing from military rule to civilian rule in Nigeria significantly increased the GDP of the country.

Analyses of unified congestion measures for interrupted traffic flow on urban roads

To study the congestion of interrupted flow on urban roads, a comprehensive evaluation method is proposed. First, based on the results of correlation analysis between different parameters of interrupted flow, the traffic parameters of interrupted traffic flow are divided into two categories： the basic parameters and the operation parameters. Polynomial regression is used to formulize the nonlinear relationships between the basic parameters and the operation parameters. Then, the congestion model incorporating both operational and volume characteristics of traffic flow is proposed. The inputs of the model are the basic parameters, while the output is a dimensionless index value between 0 and 1. Finally, the proposed methods are compared with existing evaluation measures of congestion. Results show that the proposed indices can capture the variation of both the basic parameters and the operation parameters, which is more balanced compared with the existing evaluation measures.

ECCM scheme against interrupted sampling repeater jammer based on time-frequency analysis

The interrupted sampling repeater jamming（ISRJ） is an effective deception jamming method for coherent radar, especially for the wideband linear frequency modulation（LFM） radar. An electronic counter-countermeasure（ECCM） scheme is proposed to remove the ISRJ-based false targets from the pulse compression result of the de-chirping radar. Through the time-frequency（TF） analysis of the radar echo signal, it can be found that the TF characteristics of the ISRJ signal are discontinuous in the pulse duration because the ISRJ jammer needs short durations to receive the radar signal. Based on the discontinuous characteristics a particular band-pass filter can be generated by two alternative approaches to retain the true target signal and suppress the ISRJ signal. The simulation results prove the validity of the proposed ECCM scheme for the ISRJ.

Using Interrupted Time Series Design to Analyze Changes in Hand, Foot, and Mouth Disease Incidence during the Declining Incidence Periods of 2008-2010 in China

Objective To identify patterns of hand, foot and mouth disease （HFMD） incidence in China during declining incidence periods of 2008, 2009, and 2010. Methods Reported HFMD cases over a period of 25 months were extracted from the National Disease Reporting System （NDRS） and analyzed. An interrupted time series （ITS） technique was used to detect changes in HFMD incidence rates in terms of level and slope between declining incidence periods of the three years. Results Over 3.58 million HFMD cases younger than 5 years were reported to the NDRS between May 1, 2008, and May 31, 2011. Males comprised 63.4% of the cases. ITS analyses demonstrated a significant increase in incidence rate level （P〈0.0001） when comparing the current period with the previous period. There were significant changes in declining slopes when comparing 2010 to 2009, and 2010 to 2008 （all P〈O.O05）, but not 2009 to 2008. Conclusion Incremental changes in incidence rate level during the declining incidence periods of 2009 and 2010 can potentially be attributed to a few factors. The more steeply declining slope in 2010 compared with previous years could be ascribed to the implementation of more effective interventions and preventive strategies in 2010. Further investigation is required to examine this possibility.

Effects of interrupted ageing and asymmetric rolling on microstructures, mechanical properties, and intergranular corrosion behavior of Al-Mg-Si-Zn alloy

Effects of interrupted ageing(T6I6) and asymmetric rolling on microstructures, mechanical properties, and intergranular corrosion(IGC) behaviors of Al-Mg-Si-Zn alloy were investigated. Results showed that the T6 alloy has the lowest strength and the worst IGC resistance, while the T6I6 alloy has higher strength and better IGC resistance.What’ s more, the alloy treated by pre-rolling deformation has higher strength and better IGC resistance;and the alloy treated by the pre-asymmetry rolling achieves the highest strength, the best IGC resistance and lower elongation. The mechanical properties depend on microstructures such as the grain size, texture, dislocation density and precipitation, the grain boundary misorientation and grain boundary microstructure are responsible for the IGC resistance.

Does Monetary Support Increase the Number of Scientific Papers？ An Interrupted Time Series Analysis

Purpose： One of the main indicators of scientific production is the number of papers published in scholarly journals. Turkey ranks 18th place in the world based on the number of scholarly publications. The objective of this paper is to find out if the monetary support program initiated in 1993 by the Turkish Scientific and Technological Research Council （TUBITAK） to incentivize researchers and increase the number, impact, and quality of international publications has been effective in doing so.Design/methodology/approach： We analyzed some 390,000 publications with Turkish affiliations listed in the Web of Science （WoS） database between 1976 and 2015 along with about 157,000 supported ones between 1997 and 2015. We used the interrupted time series （ITS） analysis technique （also known as ＂quasi-experimental time series analysis＂ or ＂intervention analysis＂） to test if TOBITAK＇s support program helped increase the number of publications. We defined ARIMA （1,1,0） model for ITS data and observed the impact of TOBiTAK＇s support program in 1994, 1997, and 2003 （after one, four and 10 years of its start, respectively）. The majority of publications （93%） were full papers （articles）, which were used as the experimental group while other types of contributions functioned as the control group. We also carried out a multiple regression analysis.Findings： TUBITAK＇s support program has had negligible effect on the increase of the number of papers with Turkish affiliations. Yet, the number of other types of contributions continued to increase even though they were not well supported, suggesting that TUBITAK＇s support program is probably not the main factor causing the increase in the number of papers with Turkish affiliations. Research limitations： Interrupted time series analysis shows if the ＂intervention＂ has had any significant effect on the dependent variable but it does not explain what caused the increase in the number of papers if it was not the intervention. Moreover, except the＂intervention＂, other ＂event（s）＂ that might affect the time series data （e.g., increase in the number of research personnel over the years） should not occur during the period of analysis, a prerequisite that is beyond the control of the researcher. Practical implications： TUBITAK＇s ＂cash-for-publication＂ program did not seem to have direct impact on the increase of the number of papers published by Turkish authors, suggesting that small amounts of payments are not much of an incentive for authors to publish more. It might perhaps be a better strategy to concentrate limited resources on a few high impact projects rather than to disperse them to thousands of authors as ＂micropayments.＂ Originality/value： Based on 25 years＇ worth of payments data, this is perhaps one of the first large-scale studies showing that ＂cash-for-publication＂ policies or ＂piece rates＂ paid to researchers tend to have little or no effect on the increase of researchers＇ productivity. The main finding of this paper has some implications for countries wherein publication subsidies are used as an incentive to increase the number and quality of papers published in international journals. They should be prepared to consider reviewing their existing support programs （based usually on bibliometric measures such as journal impact factors） and revising their reward policies.

Skin-Adhesive Tape versus Interrupted Suture in Episiotomy Skin Repair: Randomized Control Trial

Introduction: The ideal method for perineal repair should be quick, easy to perform and preferably, with minimal pain. Aim: To compare skin adhesive tape and interrupted?absorbable subcuticular suture for episiotomy repair after birth as regard postoperative pain, skin closure time and wound infection. Design: Prospective double-blinded randomized controlled trial. Methods: Three-hundred qualified patients were equally distributed between two groups. Group 1 underwent skin repair with skin adhesive tape, while group 2 underwent the currently traditional method for perineal repair by interrupted suture. Pain was evaluated at 2, 4, 6 and 12 hours after birth then daily until one week using Wong-Baker faces pain rating scale with verbal expression for pain intensity as primary outcome. Skin closure time and wound infection were also evaluated as secondary outcomes. Results: Statistically significant difference in pain was?found at 4 and 6 hours, and 3,?4,?5 and 7 days after perineal repair in favor of the adhesive tape group (p = 0.04 and 0.02 respectively) (p = 0.002, 0.002, 0.003 and 0.001 respectively). No statistically significant difference was found in skin closure time between both groups, and no cases of wound infection occurred in both groups (p = 0.3). Conclusion: Skin adhesive tape may be superior to skin suturing in decreasing pain resulting from perineal repair after birth;however, further studies are needed to assess long-term effects, calculate costs and accurately measure patients’ satisfaction, which were not addressed in this study.

An Interrupted Time Series Analysis of COVID-19 Positivity before, during and after Lockdown in Four States of India

Objectives: The objective of this study was to examine the impact of large scale non-pharmaceutical interventions on COVID-19 pandemic. Methods: We used interrupted time series analysis (ITS), a quasi-experimental model to evaluate the effect of interventions in four states of India by comparing the COVID-19 positivity before lockdown, during lockdown and opening-up period. Results: The positivity in all the four states declined during lockdown and the trends reversed soon after the lockdown measures were relaxed as the states opened-up. The rate of reduction of positivity was significantly different between states. Between the lockdown and opening-up period, an increase in positivity was recorded in all the states with significant variation between states. Conclusion: The analysis provides conclusive evidence that the lockdown measures had a positive effect in reducing the burden of COVID-19 and establishes a causal relationship.

Isolated Type C Interrupted Aortic Arch in Adult:Extra-anatomic Repair Using Circulatory Arrest

INTERRUPTED aortic arch （IAA） is a rare congenital malformation that occurs in 5.8 per million live births. 1 IAA was thought to be incompatible with life once the ductus arteriosus closed. However, ifextensive collateral circulation is p possible. We report treated successfully an unusual resent at case of with extra-anatomic under deep hypothermia drculatory arrest birth survival is IAA, who was aortic repair

Isolated interrupted aortic arch in an adult:A case report

BACKGROUND Interrupted aortic arch(IAA)is a rare congenital heart disease defined by an interruption of the lumen and anatomical continuity between the ascending and descending major arteries.It is usually found within a few hours or days of birth.Without surgery,the chances of survival are low.If IAA patients have an effective collateral circulation established,they can survive into adulthood.However,IAA in adults is extremely rare,with few reported cases.CASE SUMMARY A 27-year-old woman presented with a 6-year history of progressively worsening shortness of breath and chest tightness on exertion.She had cyanotic lips and clubbing of the fingers.A transthoracic echocardiogram revealed an enlarged heart and dilation of the main pulmonary artery.There was an abnormal 9 mm passage between the descending aorta and pulmonary artery.The ventricular septal outflow tract had a 14 mm defect.Doppler ultrasound suggested a patent ductus arteriosus and computed tomographic angiography showed the absence of the aortic arch.The diagnoses were ventricular septal defect,patent ductus arteriosus,and definite interruption of the aortic arch.Although surgical correction was recommended,the patient declined due to the surgical risks and was treated with medications to reduce pulmonary artery pressure and treat heart failure.Her condition has been stable for 12 mo of follow-up.CONCLUSION Although rare,IAA should be considered in adults with refractory hypertension or unexplained congestive heart failure.

Difference and similarity between type A interrupted aortic arch and aortic coarctation in adults:Two case reports

BACKGROUND Aortic coarctation(CoA)is usually confused with interrupted aortic arch(IAA),especially adult type A interrupted aortic arch,due to their similar anatomical location.Although the main difference between them is whether arterial lumen exhibits continuity or not,the clinical manifestations are similar and connection exists between them.Adult type A IAA is considered as an extreme form of CoA,which is complete discontinuity of aortic function and lumen caused by degenerative arterial coarctation.This paper reports two cases(interrupted aortic arch and severe aortic coarctation)to analyze the difference and similarity between them.CASE SUMMARY The two cases of patients presented with hypertension for many years.Computed tomography angiography showed that the aortic arch and descending aorta were discontinuous or significantly narrowed with extensive collateral flow.The IAA patient refused surgical treatment and blood pressure could be controlled with drugs.While the CoA patient underwent stent implantation because of uncontrollable hypertension,the blood flow recovered smoothly and the blood pressures at both ends of the stenosis returned to normal after surgery.CONCLUSION Adult type A IAA and CoA have difference and similarity,and type A IAA is associated with CoA to a certain extent.The treatment method should be chosen based on the patient's clinical symptoms rather than the severity of the lesion.

Natural History of Kawashima Palliation in Single-Ventricle and Interrupted Inferior Vena Cava Heart Disease in China 11 Years Result

Background:The long-term outcomes of patients treated with a Kawashima procedure and keeping the antegrade pulmonary blood flow(AnPBF)in single-ventricle(SV)and interrupted inferior vena cava(IVC)heart disease is still uncertain as yet.Methods:We investigated 18 patients who underwent the Kawashima procedure with SV physiology and an interrupted IVC between January 2009 and June 2018,perioperative,operative and postoperative characteristics were recorded.Results:A total of 18 patients underwent the Kawashima procedure at a median age of 2.7 years(range 0.5–24.7 years),of which 12(66.7%)were male and 6(33.3%)were female.The mean saturation was 76.2±8.5%in preoperative period and 94.2±2.2%in postoperative period.All patients had kept AnPBF.The median duration of mechanical ventilation was 12 h(range 2.5–22.5 h)and the median duration of pleural drainage was 5 days(range 2–27 days).The median hospital stay was 9 days(range 6–70 days).There was no operative death and no mortality was seen in early postoperative period.Follow-up was 100%completed,with an average follow-up period of 6.1±2.7 years(range 1–11 years).4 patients died during the follow-up.The overall 5 and 10 years’survival rates estimated by Kaplan-Meier method were 88%and 68%,respectively.Although there were no significant differences in the duration of postoperative follow-up between the death group and the survival group(p>0.05),the major systemic ventricular end-diastolic diameter(SVEDD)(p=0.018)and the degree of AVVR(p=0.001)showed significant difference between the two groups.The diameters of main pulmonary artery showed significant growth in both the death group(p=0.015)and the survival group(p=0.012)over time.SVEDD had no significant increase in the survival group(p=0.665)but was significantly larger in the death group(p=0.014).Multivariable risk factors of late mortality in patients treated with Kawashima procedure were follow-up AVVR(p=0.044;HR:3.124;95%CI:1.030–9.473)and SVEDD(p=0.031;HR:9.766;95%CI:1.226–77.8).14 patients(100%)were all in New York Heart Association(NYHA)functional class I and the mean saturation was 93±2%at last follow-up.Only one patient finished Fontan completion.Conclusions:The Kawashima procedure with AnPBF can be safely performed with acceptable early and long outcomes.Although some previous studies have shown the risk of pulmonary arteriovenous malformations(PAVMS)after Kawashima procedure in the mid-and long-term,our findings are in contradiction with it.No PAVMs occurred in all the survivors.Kawashima procedure with open AnPBF may be a good option for unsuitable Fontan candidates.

Perioperative anesthetic management of interrupted aortic arch associated with severe pulmonary hypertension in a young adult: case report and review of the literature

The interrupted aortic arch (IAA) is rare congential heart defect and entails a very poor prognosis without surgical treatment. We describe a young adult patient with IAA associated with severe pulmonary hypertension and discuss the perioperative anesthetic management of single-stage surgical correction in this patient. Preoperative anesthetic preparation with better understanding of the malformation, intraoperative hemodynamic monitoring, and adequate alveolar ventilation in the perioperative period were all important factors contributing to a successful outcome.

Experimental Study of Heat Transfer to Flowing Air inside a Circular Tube with Longitudinal Continuous and Interrupted Fins

Experimental investigations have been performed to determine the detailed module-by-module pressure drop and heat transfer coefficient of turbulent flow inside a circular finned tube. The tubes are provided with longitudinal fins continuous or interrupted in the stream wise direction by arranging them both in a staggered and in-line manner. Experiments are carried out for two different fin geometries, with two numbers of fins (N = 6 and 12). All tested finned tubes have 16 modules each with length equal to the tube diameter (L = D = 30 mm). The thermal boundary condition considered here, is a uniform heat flux. The module-by-module heat transfer coefficient is found to vary only in the first modules, and then attained a constant thermally periodic fully developed value after eight to twelve modules. The results also showed that in the periodic hydrodynamic fully developed region, the value of the pressure drop along the tube with continuous fins is greater than that of the in-line arrangement, and lower than that of the staggered arrangement. Furthermore, the results showed that in the periodic fully developed region, the tube with continuous fins produces a greater value of the heat transfer coefficients than that the tube with interrupted fins, especially through a high range of Reynolds number (5 × 104 > Re > 2 × 104). The tube with Staggered arrangement of fins produces a greater value of the heat transfer coefficient than the tube with continuous fins and the in-line arrangement finned tube at low Reynolds number (Re < 1.2 × 104).). It was found that the fins efficiency is greater than 90 percent;in the worst case (maximum Reynolds number with continuous fins tube).

Interrupted Etanercept Therapy: A New Case Report

Psoriasis is a chronic, immune-mediated, inflammatory disease with a high prevalence in the general population (2%). The anti-tumor necrosis factor receptor etanercept is Food and Drug Administration (FDA) approved for the treatment of moderate-to-severe plaque psoriasis. Both continuous and interrupted etanercept therapy is effective and well-tolerated. This report aims to document a new case presentation of psoriasis on intermittent etanercept injection throughout 36 weeks with long-lasting sustained efficacy and no risk factor. Case Report: A 39-year-old adult male patient with long-standing chronic plaque psoriasis for 15 years duration without joint involvement started loading dose treatment of etanercept injection in whom due to his work circumstances not taken maintenance therapy and showed-up at the clinic after 36 weeks from first induction therapy when partial relapse of psoriatic lesions appear in last week with continued improvement when reintroducing loading treatment on followed-up over the next 36 weeks. Conclusion: Intermittent etanercept therapy considers effective for 36 weeks with prolonging sustained efficacy and without adverse effect.

Research on arc root stagnation when small current is interrupted in self-excited circuit breaker

The self-excited DC air circuit breaker(SE-DCCB)has been widely used in urban rail transit due to its excellent stability.It can realize forward and reverse interruption,but has difficulty interrupting small currents due to the phenomenon of arc root sticking at the entrance of the arc chamber in the splitting process,which is known as arc root stagnation.A coupling model of the self-excited magnetic field and magnetohydrodynamics is established for the SE-DCCB with the traditional structure.The magnetic field,temperature and airflow distribution in the arc chamber are investigated with an interrupting current of 150 A.The simulation results show that the direction and magnitude of the magnetic blowout force are the dominant factors in the arc root stagnation.The local high temperature of the arc chamber due to arc root stagnation increases the obstruction effect of the airflow vortex on the arc root movement,which significantly increases the arc duration time of small current interruption.Based on the research,the structure of the magnetic conductance plate of the actual product is improved,which can improve the direction and magnitude of the magnetic blowout force at the arc root so as to restrain the development of the airflow vortex effectively and solve the problem of arc root stagnation when the small current is interrupted.The simulation results show that the circuit breaker with improved structure has a better performance for a small current interruption range from 100 A to 350 A.