High-voltage DC arrester is one of the key equipment for overvoltage protection of ultra-high voltage DC (UHVDC) transmission system. This device plays a decisive role in the insulation level of the ...whole process. The current distribution between resistance pieces of multi-column parallel arresters is non-uniform, which affects the overall energy absorption capacity of arresters. First, a real failure case of ±500 kV Xiluodu-Nuozhadu HVDC project is introduced. Then, the analysis of the specific failure case is proposed. Finally, a corresponding model is built on PSCAD/EMTDC to study the current distribution characteristics.
The development of defects in basin insulators inside a GIS (gas-insulated metal-enclosed switchgear) could trigger partial discharges under long-term working voltage, threatening safe GIS operation. ...In this paper, the ultrasonic pulse-echo method was proposed to detect large-scale basin insulators. And an ultrasonic pulse-echo system was set up, including an ultrasonic generator, a transducer and so on. Among them, the ultrasonic generator has been improved to obtain the original ultrasonic waveform. Then ultrasonic tests were carried out on the thickness of large-scale basin insulators, and the type and appropriate frequency of the ultrasonic transducer was proposed. Besides, a void in the epoxy composite specimen was detected and located. The results showed that the ultrasonic pulse-echo method could penetrate 15mm \sim70 mm thick basin insulators, and the 1P20 transducer has a better effect on detecting defects than the 1.5P14. The ultrasonic pulse-echo method is feasible for detecting defects in large-scale basin insulators.
Basin insulators are significant components in gas-insulated metal-enclosed switchgear (GIS). The internal stress in basin insulators can cause cracks, and other insulation faults. In this research, ...a method for measuring the internal stress based on the ultrasonic longitudinal critically refracted (LCR) waves is proposed. Some epoxy specimens were manufactured, of which the material and the manufacture process were the same as the 252 kV GIS basin insulators. An ultrasonic LCR waves system was set up to investigate the internal stress of epoxy specimens under the compression in the range of 0-50 MPa. 2.5 MHz frequency can provide a better performance than 0.5 MHz frequency when the LCR wave method is used. The results show that the LCR propagation time is linearly decreased with compressive stress increasing, and the acoustoelastic coefficient is calculated to be -4.950. The probe placement configurations are proposed in measuring the circumferential stress and axial stress in the basin insulators.
Gas-insulated metal-enclosed switchgear (GIS) is widely used in UHV transmission system and power distribution system in major city, and it has become the preferred equipment for the construction of ...smart grid. As weakness components of GIS, the uneven distribution of the internal stress of the basin insulator will lead to the whole insulator cracking and even partial discharge, which will affect the safe and stable operation of GIS. Therefore, it is of great significance to study the effective detection method of insulator internal stress for the safe operation of GIS. This paper introduces various ultrasonic internal stress detection methods and their applications from the perspective of ultrasonic type, This paper introduces various ultrasonic internal stress detection methods and their applications from the perspective of ultrasonic type, analyzes the characteristics, limitations and research status of various ultrasonic internal stress detection methods, such as ultrasonic longitudinal wave, transverse wave, combined longitudinal and transverse wave, critical refraction longitudinal wave and Rayleigh wave, and discusses their application prospects in pot insulator.
The double-fracture disconnect switch(DDS) is a solution to continue operating without shutting down during GIS extension and withstand tests, which is designed as an nonstandard structure. In order ...to verify that the DDS satisfies the actual operating conditions. In this paper, the 3D simulation models of DDS for the mechanical, electrical, thermal field are established by ANSYS. The simulation calculation of mechanical strength, insulation strength and current-carrying capability of the DDS are carried out. In addition, the insulation test, temperature-rise test, dynamical thermal stability test, mechanical life test, shell water pressure test are carried on the real DDS as well. The results show that the maximum stress of the shell is 235.08MPa, and the maximum stress of cover plate is 114.86MPa, which are both less than the allowable stress. It also shows that the electrical field of each component in the DDS is lower than the allowable field strength. As for the temperature test, the maximum temperature rise of sliding joint and the shell are 56.5K and 17.3K. Temperature rise of both internal conductor and shell meet the requirements. In sum, the experimental results consistent with the simulation calculation. The DDS has been applied to 6 standby expansion intervals of 220kV GIS in the ±800kV Dong-Fang converter station.
The condition of arc nozzle in a gas chamber is significant for the health of a circuit breaker, especially for high frequency interruption circumstance such as AC filter circuit breakers in HVDC ...system. However, few methods can assess the ablation state of a nozzle without opening the gas chamber. To solve this issue, this research proposes an non-intrusive way to diagnose the nozzle ablation condition. The method is based on tracking the SF 6 decomposed products as the circuit breaker under test is in operation. Additionally, a SF 6 gas chromatography was designed to record and analyse the changing trends of SF 6 decomposed products every 20 minutes in a real-time mode. The results show that CF 4 can be treated as a characteristic component to reflect the nozzle ablation status. The CF 4 content is found to highly correlated with the loss of the nozzle materials and the increment of making and breaking energy.
Compared with the overhead transmission line, gas insulated transmission lines (gil) occupies less land area, has higher insulation reliability, and is increasingly widely used in the field of power ...transmission. under actual working conditions, gil will withstand a variety of voltages, such as ac, dc and impulse voltages. under such conditions, electric charges will accumulate on the surface of the gil tri-post insulator, which will enhance local electric field and affect the surface flashover voltage. based on the measurement method of electrostatic capacitance probe, a surface charge measurement device for gil tri-post insulator was developed in this paper to capture the surface charge accumulation characteristics of tri-post insulator under different voltages insf6. according to the structural characteristics of the tri-post insulator, a set of three-dimensional motion control mechanism is designed to control four probes to scan the surface of insulator in the post zone, the sphere zone and the junction zone of post and sphere with high precision. the calibration experimental results show that the system has high sensitivity and accuracy. for the side probe of post zone, the charge resolution is 0.0290c/(m2·nv) and the spatial resolution is 4.6mm2, for the 1# arc probe of post zone, the charge resolution is 0.0237c/(m2·nv) and the spatial resolution is 5.1mm2, for the 2# arc probe of post zone, the charge resolution is 0.0245c/(m2·n v) and the spatial resolution is 5.0mm2, for the sphere probe, the charge resolution is 0.0165c/(m2·n v) and the spatial resolution is 6.7mm2
Press pack (PP) packaging technology has been applied to insulated-gate bipolar transistors (IGBTs) for high-voltage and high power density applications in recent years. The pressure distribution ...within PP IGBTs is very important because it affects both the electrical and thermal contact resistances, thermal cycling capability, and short-circuit current rating. Too much pressure will mechanically damage the chip and too little pressure will increase the thermal contact resistance, which eventually leads to chip thermal damage. In this paper, a finite-element multiphysics model cocoupled with an electrical field, thermal field, and mechanical field is proposed to analyze the collector current distribution, pressure distribution, and junction temperature distribution within PP IGBTs. The most important coupling variables, such as electrical and thermal contact resistances, for this cocoupled multiphysics model are calculated or measured by experiment through a single IGBT/fast-recovery diode chip submodule. Based on this multiphysics model, the influence of the high temperature generated by the chip's power dissipation on the pressure distribution within PP IGBTs (in the heating phase) is discussed, and then, compared with the pressure distribution in the clamping phase. The results show that the pressure distribution within PP IGBTs in the heating phase is extremely uneven and different from the value in the clamping phase. Furthermore, the mechanical model and its boundary conditions are verified through the pressure distribution experimental results in the clamping phase, which is measured based on the Fuji prescale film and the clamping test bench. Based on the simulation and experimental results, an optimization of the collector electrode and pedestal is proposed to improve the pressure distribution within PP IGBTs in the heating phase.
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•The controllable amorphization engineering on CoxFey-MOFs has been successfully realized.•The optimized amorphous Co4Fe6-MOF exhibits superior electrocatalytic OER activity.•The ...amorphous structure and the bimetallic synergistic effects could promote the improvement of catalytic OER activity.
Deliberate tailoring of the metal–organic frameworks (MOFs) composition and structure could provide limitless flexibility for the development of highly efficient electrocatalysts toward oxygen evolution reaction (OER). However, the changes in crystallinity of MOFs related to the composition manipulation have seldom been explored for the catalytic OER activity. Herein, we realize the controllable amorphization engineering on CoxFey-MOFs from crystalline to amorphous state by deliberately adjusting the ratio of Co/Fe precursors introduced within the MOFs. While crystalline MOFs are formed with initially dominating the contribution of Co ions, amorphous MOFs are obtained when the amount of Fe ions exceeds 60%. Theoretical findings propose that the defects formation energies of CoxFey-MOFs can be dramatically reduced with the decrease of Co/Fe ratio, which make the long-range disorder structure be readily formed with abundant defects. The disorder structure and the tunable ratio of Co/Fe enable to endow the bimetallic CoxFey-MOFs with abundant active sites and fast charge transfer, thus boosting the catalytic activity towards OER. It is found that the optimized amorphous Co4Fe6-MOF can deliver the current density of 10 mA cm−2 only at a low overpotential of 241 mV with extremely small Tafel slope of 30.1 mV dec-1. The present work enriches the understanding on the crystalline-to-amorphous transformations and sheds light on the way for the applications of amorphous MOFs nanomaterials in water splitting field.
Premature ovarian insufficiency (POI) is associated with severe physical damage and psychological burden on women. Transplantation of exosomes is an encouraging regenerative medicine method, which ...has the potential for restoring ovarian functions on POI with high efficiency. This study aims at evaluating the therapeutic efficacy of human umbilical cord mesenchymal stem cell-derived exosomes (hUCMSC-Exos) on ovarian dysfunction of POI and the role of Hippo pathway in this exosome-mediated treatment.
POI mice models were established through intraperitoneal injection of cyclophosphamide. Subsequently, transplantation of hUCMSC-Exos was conducted to administer POI mice. Ovaries and plasma of these mice models were harvested after two weeks of treatment. Ovarian morphology and follicle number were assessed by hematoxylin and eosin staining. Moreover, ELISA was used to detect hormone levels, which are related to ovarian function in serum. To assess the recovery of reproductive ability, we recorded the rate of pregnancy, the amount of offspring, and the time of birth in different groups. To explore the underlying mechanisms of exosome-mediated treatment for ovarian function recovery, the proliferation of ovarian cells
was detected by immunohistochemistry and immunofluorescence staining. Additionally, we conducted EdU and CCK-8 assays to assess the proliferative ability of ovarian granulosa cells (GCs) that were cultured
. Western blot analysis was conducted to estimate the proteins levels of Hippo- and proliferation-associated molecules
.
After transplantation of hUCMSC-Exos, the ovarian function-related hormone levels and the number of ovarian follicles returned to nearly normal degrees. Meanwhile, there was a significant improvement in reproductive outcomes after exosomal treatment. Furthermore, the improvement of ovarian function and proliferation was associated with the regulation of Hippo pathway.
, co-culture with exosomes significantly elevated the proliferation of ovarian GCs by regulating Hippo pathway. However, the positive effects on the proliferation of GCs were significantly depressed when key Hippo pathway molecule was inhibited.
This study suggested that hUCMSC-Exos promoted ovarian functions and proliferation by regulating the Hippo pathway. Therefore, exosomal transplantation could be a promising and efficient clinical therapy for POI in the near future.
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