With the development of wide-bandgap high-voltage power devices with high power density, such as SiC MOSFET, packaging insulation has attracted increasing attention for securing reliability. Packaging insulation of power modules withstands constant unipolar square wave voltages due to the anti-parallel diode of IGBT or body diode of MOSFET, which makes it vulnerable to space charge accumulation. However, it is hard to observe the space charge dynamic behavior under the unipolar square wave voltage since the rising or falling time of the square wave is relatively short, hence the ultra-fast space charge measurement is required. In this paper, a sub-megahertz space charge measuring method based on a high repetition rate pulsed electro-acoustic method is proposed. The pulse generator uses the Blumlein line and SiC MOSFET to form nanosecond pulse voltage with repetitive frequency up to 3 MHz. Then, the transient space charge waveform of silicone elastomer for packaging insulation under square wave voltage with high dV/dt is obtained. It is found the fast rising and falling edge of the high square wave voltage can generate electromagnetic interference to the acoustic-electric signal, which should be carefully handled. The proposed sub-megahertz space charge measurement method can provide references for the research of transient charge transport behavior and failure mechanism of high-voltage power module packaging insulation.
Web-based simulations are computer simulations through a web browser, which are expected to be used not only for remote work but also for education. We have developed a web-based simulation of particle motion in ion wind flow using three.js that is an open-source JavaScript library for simplify WebGL coding. Ionic wind is an airflow induced by electrostatic forces during corona discharges. In general, finite element method (FEM) is used to calculate an ionic wind. However, it is difficult for the FEM to represent the behavior of charged particles in ionic winds. To simulate the charged particle behavior, we calculate the motion of tracer particles in an ionic wind. The calculation results are good agreement with experimental results using a high-speed camera.
In this work, we present the development of a miniature surface plasmon resonance (SPR) sensor chip using the Kretschmann configuration. The SPR sensor chip incorporates a polymeric prism made from Norland Optical Adhesive 61 (NOA 61). By utilizing NOA 61 instead of a conventional prism, we overcome certain limitations associated with conventional SPR spectroscopy. We employed the confined sessile drop technique to fabricate the NOA 61 polymeric prism, which offers several advantages, including simplicity, low-cost fabrication, and precise control over lens parameters. A liquid NOA 61 was dropped directly onto a flat circular disk with a 6-mm diameter made of poly(dimethyl siloxane) (PDMS). The sharp edge of the PDMS circular disk facilitated controlled formation and the desired amount of the liquid NOA 61, resulting in the formation of a hemispherical prism. Subsequently, UV curing was employed to solidify the NOA 61, then obtaining the NOA 61 polymeric prism. To complete the miniature SPR sensor chip, 3 nm-thick chromium layer, and 47 nm-thick gold layer were evaporated onto the planar side of the NOA 61 polymeric prism and then mounted on a microfluidic cell fabricated using a 3D printer. The resulting SPR excitation curves were observed in the visible region and exhibited a refractive index independence sensitivity of 885.4 nm/RIU. Furthermore, we demonstrated the capability of the miniature SPR sensor chip to detect nanomaterials.
A composite material with higher thermal conductivity and acceptable breakdown strength has been developed. An electrostatic adsorption method produced a thermoplastic polyimide (tpPI)/ hexagonal boron nitride (hBN) composite to create a thermally conductive composite insulating material. The flaky surface of the hBN particles was oriented vertically to the sample thickness direction (CMV sample) or parallel to the sample thickness direction (CMP sample). The transferred/accumulated charge amount was measured using the Q(t) method to understand the insulating property. As a result, the charge amount ratio (Q(300)/Q0(2)) of the CMP sample at 30°C is higher than that of the CMV sample. In addition, the temperature-dependent transferred/ accumulated charge amount of the CMP sample was also comparatively higher than that of the CMV sample. This is probably attributed to the tpPI/hBN interface, a potential electrical weak point, and is parallel to the CMP sample's thickness (electric field) direction.
On the surface of a stress relief cone installed in a prefabricated joint and termination, precipitate would be generated during long-term operation. The precipitate could lead to affect insulation performance for XLPE cable systems. However, the relationship between the state of precipitate, such as the shape, position, amount, and color tone, and insulation performance has not been clarified. Additionally, photography cannot record the state of precipitate without distortion because the stress relief cone mainly consists of curved surfaces. This paper aims to digitize surface condition of a stress relief cone into 3D objects that can be objectively compared with respect to the state of precipitate and deformation on stress relief cones, which are difficult to quantitatively compare each other by photography. Photogrammetry digitizes the outline and color tone of an object into a 3D object from lots of photographs taken from different shooting direction. In this paper, the stress relief cone taken from the dismantled 275 kV prefabricated termination was digitized into a 3D object with the photogrammetry and confirmed its dimensional error of 1 mm or less. This result confirmed that the 3D digitization of stress relief cones using photogrammetry can be useful for quantitative analysis of the state of precipitate.
