The remarkable characteristics of nanofibers mats electrospun are large surface area to volume ratio and high porosity, which are crucial to increase the ionic conductivity of membrane full of liquid ...electrolyte, in this aspect, electrospinning is prior to the other methods, such as dry method, wet method, etc. Therefore, fabricating the separator of Li-ion batteries by electrospinning is potential and promising. The PVDF membranes were fabricated by electrospinning. The experiment demonstrated that the main deficiency in the fabricating separators process by electrospinning was low mechanical property, which induced partial short circuits inside the cells. Several methods were presented to enhance the mechanical strength. The experiments demonstrated that the higher the solution concentration was, the stronger the mechanical strength was, and the higher the voltage was, the stronger the mechanical strength was. Additionally, the spherical hat collection target instead of conditional plane target was applied in the electrospinning system, as a result, the thickness of the membrane was more uniform and the fiber diameter was also more uniform. Therefore, the charge and discharge capacity of the coin type cell composed of the separator collected by spherical hat target exceeded the plane target, and the electrospinning separators exceeded the commercial polypropylene separator.
► The effect of the electrolyte on MnO
2 has been investigated systematically by using alkaline (Li
+, Na
+, or K
+) and alkaline-earth (Mg
2+, Ca
2+, or Ba
2+) metal cations as an ion probe. ► A ...very high capacitance of 357.9
F
g
−1 has been obtained when Ca
2+ ion is used as electrolyte cation. ► The reversible insertion–extraction of cation instead of proton or anions is responsible for the pseudo-capacitive behavior of manganese dioxide. ► The capacitance of MnO
2 has been doubled by replacing univalent cation with bivalent cation at a close cation activity.
Effect of the electrolyte particularities on manganese dioxide in the neutral electrolytes containing alkaline (Li
+, Na
+, or K
+) and alkaline-earth (Mg
2+, Ca
2+, or Ba
2+) metal cations for electrochemical capacitor is investigated by cyclic voltammetry and electrochemical impedance spectroscopy. A very high capacitance of 357.9
F
g
−1 is measured when Ca
2+ ion is used as electrolyte cation. The results show that cations of the electrolyte instead of proton or anions are responsible for the pseudo-capacitive behavior of manganese dioxide. The capacitance of manganese dioxide is found to depend strongly on the electrolyte particularities, for example, pH value, cation and anion species, and salt concentrations. A logarithmic dependence of capacitance of MnO
2 on cation activity is obtained for all alkaline and alkaline-earth metal cations. The capacitance of MnO
2 can be doubled by replacing univalent cation with bivalent cation at a close cation activity.
In China high temperature vulcanized (HTV) silicone rubber has been applied to manufacture the sheds and sheath of composite insulators for decades. Being exposed to environmental stressors including ...sunlight, UV radiation, oxidization, electrical stress and moisture throughout the whole operation period, various aging phenomena could be observed, among which color fading and hardening are two important indexes which may be directly related to the performance of composite insulators. According to polymer aging theory, thermo-oxidative could be the main aging reaction leading to the hardening of HTV silicone rubber and in this paper, Thermogravimetric Analysis (TGA) combined with Differential Scanning Calorimetry (DSC), Infrared Spectroscopy (IR) and Mass Spectroscopy (MS) are applied to study the degradation and decomposition process of HTV silicone rubber in air (oxidizing atmosphere) and nitrogen (inert atmosphere) respectively. 18 composite insulator specimens have been collected and their color fading degree, hardness, crosslink density as well as thermal performance have been measured and calculated. A correlation analysis showed that physical crosslink density had a strong positive relation with hardness of specimens whereas chemical crosslink density showed negative relations with hardness. It is concluded that TGA is an effective method to simulate and study the thermo-oxidative aging process of HTV silicone rubber and the measurement results of crosslink density shows that decomposition and over crosslinking reactions have taken place simultaneously in HTV silicone rubber and led to the aging of composite insulators together.
The surface discharge of natural polluted post insulators in rain is an important factor which affects the external insulation of HVDC converter stations. With the artificial contamination flashover ...tests in rain for porcelain post insulators, this paper has obtained the flashover process and discharge characteristics of the test samples under artificial rain condition. It has been observed that the discharge of water droplet on the shed edge plays a very important role in the whole process of pollution flashover in rain. When a water droplet hangs on the shed edge, the maximum electric field strength appears in the vicinity of vertices, rather than the lateral area of the water droplet. Thus, the streamer propagates only in the direction of the air gap between sheds. Moreover, the influence of raining conditions including intensity and conductivity on the flashover voltage has been investigated. Test phenomena also indicate that due to the different damp and dry band conditions, surface discharge characteristics of post insulator in rain are different with that in fog, which lead to different flashover voltages. This study provides a new understanding for the HVDC insulator pollution flashover in wet environment.
When polluted insulators get wet, the flashover voltage will decrease dangerously, threatening the stability of the power grid. It is known that moisture is a necessary condition for the pollution ...flashover accident, for a great deal of research has been carried out concerning the effect of humidity on the moisture of insulators. As the climate in the inland area is dry and the humidity is low, the pollution flashover accident tends to occur early in the morning, when condensation on the surface of the insulator is the most serious due to the temperature difference between the insulator and ambient air. In order to study the effect of temperature difference on pollution layer wetting process, and improve the accuracy of the condition assessment and flashover alarming, this paper analyzes the source, the existence form and the variation tendency of the water absorption of the polluted layers under the temperature difference based on the leakage current of insulators. In addition, for verifying the effects of the temperature difference during the wetting process of the pollution layers quantitatively, a series of laboratory tests have been performed in a multifunction artificial climate chamber. The results indicate that the water absorption of the polluted layer is directly proportional to the temperature difference under the medium humidity, which may provide some valuable reference for the on-line monitoring of insulator contamination in inland arid areas.
The leakage current of the insulator during wetting process can be converted to the surface conductivity by combining the operating voltage and insulator shape. Furthermore, the salt deposit density ...(SDD) of the insulator with natural contamination can be calculated and the contamination degree can be evaluated. However, due to the heating effect of the leakage current, some dry bands could be generated on the insulators' surface during the wetting process, which makes the leakage current appear smaller than the condition when the insulator is moist completely. In this paper, leakage current trends of two different types of insulators during the wetting process were measured and the surface conductivity was calculated. The test results showed that, due to the influence of the partial electric arc near the pin, the surface conductivity deduced from the leakage current was smaller than that of the actual surface conductivity of the contamination layer, but for certain types of insulators, there was a relatively fixed correlation between them.
The natural contamination components vary in different areas. NaCl is the major soluble salt on the surface of insulators in coastal areas. In contrast, the proportion of CaSO 4 in inland areas is ...greater, which makes pollution flashover voltage of insulators have large scatter. As a result, the relationship between ESDD and pollution flashover voltage is unclear. However, in the artificial contamination pollution flashover experiments, NaCl is often utilized as the single soluble salt in the contamination, and there is a clear negative exponential relationship between the pollution flashover voltage and the SDD. In this paper, the relationship among ESDD, contamination components and surface conductivity of insulators under saturated moisture is analyzed. On this basis, the ratio of surface conductivity to ESDD is proposed to describe the difference of soluble salt components in natural contamination. Experimental results indicate that the ratio of surface conductivity of the polluted insulators under saturated moisture to ESDD is in the range of 14-866. This ratio is inversely proportional to the proportion of CaSO 4 in the soluble salts of the natural contamination. If two of the three parameters, namely, the surface conductivity, ESDD, and contamination components, are measured, the remaining one can be calculated. The ratio of surface conductivity to ESDD can be utilized as a parameter to describe the components of natural contamination.
In recent years, some hollow core composite insulators, of which housings were made of liquid silicone rubber (LSR) of current and voltage transformers used in China Southern Power Grid have showed ...different levels of degradation and cracking phenomena. Based on SEM, FTIR, XPS and XRD methods, analyses have been conducted from several aspects such as organic functional groups concentration, microscopic appearance, element valence etc. It is found that organic groups (mainly Si-(CH 3 ) 2 ) on the side-chains of LSR are much more vulnerable than the backbone during the degradation process, thus Si-O/Si-C absorption peak ratio could be applied to characterize the degradation level of LSR. For severely aged LSR samples, the ratio is around 1.787-2.436. The valences of Si element and Si-O, Si-C functional group relative concentration of the aged LSR surface have changed and crystal structure is formed. Macro properties tests show that the surface of aged LSR is almost hydrophilic and tracking and erosion resistance is deteriorated remarkably. It is concluded that the crystallization caused by thermal/optical oxidation over crosslinking reaction is the main reason why degradation occurred.
In order to investigate the high altitude effect on dc corona inception voltage of power transmission lines, a mobile corona cage test system was constructed. The experiments were carried in Wuhan, ...Xining, Geermu, and Nachitai, respectively. Photons released as a result of corona discharge on the conductors were detected by the ultraviolet image detector. Both positive and negative corona inception voltages could be acquired by the "tangent method" based on the measured data. The approximate linear altitude correction formulas were suggested.
The shielding failure is the occurrence of a lightning stroke that bypasses the overhead ground wires and terminates on the phase conductors. The correct design to improve the shielding effect of ...transmission line to lightning is one of the key problems of transmission line design. A numerical analysis model for shielding failure of transmission line based on electromagnetic field theory is proposed in this paper. The electrical field of the system including lightning leader, transmission line and ground is solved, the range of lightning current striking the phase conductor is obtained, and the shielding failure probability of transmission line is calculated. The lightning leader model and the critical breakdown electrical field intensity of long gap are discussed. The analyzed results by numerical analysis model are compared with those by the electrogeometric model.
