Phase field model for electric-thermal coupled discharge breakdown of polyimide nanocomposites under high frequency electrical stress

In contrast to conventional transformers, power electronic transformers, as an integral component of new energy power system, are often subjected to high-frequency and transient electrical stresses, leading to heightened concerns regarding insulation failures. Meanwhile, the underlying mechanism behind discharge breakdown failure and nanofiller enhancement under high-frequency electrical stress remains unclear. An electric-thermal coupled discharge breakdown phase field model was constructed to study the evolution of the breakdown path in polyimide nanocomposite insulation subjected to high-frequency stress. The investigation focused on analyzing the effect of various factors, including frequency, temperature, and nanofiller shape, on the breakdown path of Polyimide(PI) composites. Additionally, it elucidated the enhancement mechanism of nano-modified composite insulation at the mesoscopic scale. The results indicated that with increasing frequency and temperature, the discharge breakdown path demonstrates accelerated development, accompanied by a gradual dominance of Joule heat energy. This enhancement is attributed to the dispersed electric field distribution and the hindering effect of the nanosheets. The research findings offer a theoretical foundation and methodological framework to inform the optimal design and performance management of new insulating materials utilized in high-frequency power equipment.

Design theory and experimental investigation of the low frequency and high power rare earth magnetostrictive flextensional transducer (Ⅰ). Theoretical part

The energy relationships among all the elements, by which the magnetostrictive transducers are manufactured, in Finite Element Method (FEM) are analyzed, then the expres- sions of FEM dynamics equations and performances formulas for magnetostrictive transducers are derived. The vibrating modes of the class VII transducer and its shell vibration are calcu- lated theoretically and the results point out that there is a breathing mode and if the transducer works at this mode, the transducer will vibrate with a greater volume speed and source level.

Evolution of low-frequency noise passing through a spatial filter in a high power laser system

The theoretical model of spatial noise passing through a spatial filter is established in high power laser system under the small signal approximation. The transmission characteristic for a noise signal passing through spatial filters with different magnifications is analyzed by numerical simulation, according to the actual structure of the high power laser system. The results show that the spatial modulation period of low-frequency noise getting through the pinhole will be proportional to the magnification of the spatial filter. When the magnification is less than 1, the safe low-frequency noise will be extruded into the high-frequency region, which is the fast increasing part, and finally develops into the most dangerous part which can damage the optical devices. The conclusion of this research improves the relay imaging theory of a spatial filter and provides an important theoretical basis for a general design of high power laser systems.

Design theory and experimental investigation of the low frequency and high power rare earth magnetostrictive flextensional transducer (Ⅱ). Experimental part

Vibrating modes of the manufactured flextensional transducer and its shell are experimentally investigated. The result are consistent with the theoretical calculations. The acoustical performances for the transducer are measured: resonance frequency is 1.16 kHz in the underwater, bandwidth is 680 Hz, mechanical quality factor is 1.71, transmitting current response is 186.1 dB, electromechanical efficiency is 13.1%.

Determination of total sulfur in geothermal water by inductively coupled plasma-atomic emission spectrometry

Sulfur speciation and concentration in geothermal water are of great significance for the research and utilization of the water resources.In most situations,it is necessary to determine the total sulfur in geothermal water.In this study,the method was established for the determination of determining total sulfur content-the inductively coupled plasma-atomic emission spectrometry(ICP-AES),with the wavelength of 182.034 nm selected in spectral line of sulfur.It was identified that the optimal working conditions of the ICP-AES instrument were 1200 W for high frequency generator power 9 mm for vertical observation height,0.30 MPa atomizer pressure,and 50 r/min analytical pump speed.The matrix interference of the method was eliminated by the matrix matching method.Using this method,sulfur detection limit and minimum quantitative detection limit were 0.028 mg/L and 0.110 mg/L,respectively,whilst the linear range was 0.0-100.0 mg/L.The recovery rate of sample was between 90.67%and 108.7%,and the relative standard deviation(RSD)was between 0.36%and 2.14%.The method was used to analyze the actual samples and the results were basically consistent with the industry standard method.With high analysis efficiency,the method has low detection limit and minimum quantitative detection limit,wide linear range,good precision and accuracy,and provides an important detection method for the determination of total sulfur in geothermal water.