Analysis of dominant electric coupling coefficients on VFT phase voltage measurement in three-phase enclosed GIS

In order to measure the VFT phase voltage in three-phase enclosed GIS, 3 capacitive sensors are needed. Each capacitive sensor is coupled with the electric field of (A, B and c) three phase voltages. The elements at diagonal of electric coupling coefficient matrix are much larger than the other ones, which are called the dominant electric coupling coefficients and can be calculated approximately by an analytic expression with enough accuracy. When 3 capacitive sensors are located at the shortest point of phase A, B, and C, respectively, each phase VFT voltage (V_A or V_B or V_C) can be directly obtained by the dominant electric coupling coefficients. This paper analyses the relation between the dominant electric coupling coefficients and the geometrical parameters of the three-phase enclosed GIS, and a simplified method to calculate the dominant electric coupling coefficients is gained which is especially suitable to the experimental site.