Search

In the AC high voltage cables, XLPE has been widely used as an insulation material with its superior insulation property, mechanical property, and possibility to use at high temperature. However, despite of such an excellent insulation property, the use of XLPE in DC power transmission was somewhat limited due to the accumulation of space charge. If the space charges are accumulated, they enhance the electric field, thereby cause XLPE to breakdown during the use or polarity reversal. One way of overcoming this problem is to suppress the space charge accumulation by introducing nano particles in to XLPE. In Korea, LS Cable & System was the first who started the research on the nano composite XLPE insulation for DC Cables. Through this research, the synthesis and surface treatment of nano particles and manufacturing process of nano composite XLPE, DC conductivity and space charge characteristics were satisfied with these developed nano composites XLPE for HVDC. The space charge accumulations of nano composites XLPE are smaller than those of AC and normal DC compound, and higher electrical resistivity in the samples from pellet and cable. In case of long time testing, charge accumulation characteristics of XLPEs are something different. The 250kV DC XLPE cable was made using nano composites, and was successfully conducted the type test for LCC and VSC according to CIGRE TB 496.

We propose a super-junction trench gate MOSFET (SJ TGMOSFET) which is fabricated with a simple p-pillar forming process using deep trench and boron silicate glass (BSG) doping process technologies to reduce the process complexity. The p-pillar region is formed through lateral boron diffusion from BSG film and annealing process after the silicon deep etching. For the SJ TGMOSFET fabricated with BSG lateral diffusion, the controls of the boron concentration and the profile are important to achieve the charge balance between p-and n-pillars. Throughout the various boron doping experiments as well as process simulation, we optimize process conditions related with p-pillar depth, BSG doping concentration and diffusion temperature. Due to the trenched p-pillar, the potential of the SJ TGMOSFET more uniformly distributes and widely spreads into the bulk region of the n-drift layer comparing to the conventional TGMOSFET. The measured breakdown voltage of SJ TGMOSFET increases at least 28% than that of the conventional TGMOSFET.