Surface potential dynamics on corona charged surfaces of thick samples of EPDM and silicone rubbers have been studied and analyzed by examining the so called tdV/dt characteristics. This methodology allows for directly obtaining information about charge trap distributions in materials from measurements of potential decay without a-priori knowledge about trap parameters. More importantly, the combination of the above mentioned methodology in conjunction with measurements of other material parameters may provide information desired when analyzing the surface charge behavior on composite insulators for HVDC applications.

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Numerical analysis of UHV gapless metal-oxide surge arresters have been performed utilizing capacitive-resistive coupling transient electric field simulations. The calculations are performed in 3D and for 3-phase installations. Two types of voltage grading methods for surge arresters have been studied, with grading rings and with external grading capacitors. The results show that important advantages like a shorter and lighter arrester with improved protection performance is possible to obtain using external grading capacitors instead of grading rings.

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