Statistical approach for determining breakdown voltage of gas-insulated cables

Several goodness-of-fit test procedures were applied to DC-breakdown conditioning test results, obtained in SF₆ at 0.4 MPa in concentric-coaxial systems, and to other published data to determine whether the three-parameter Weibull distribution is the only match. The three-parameter Weibull distribution was found to be the best suited among probabilistic exponential distributions representing the area-dependent statistical characteristics of compressed-gas insulated systems. Parameters of the three-parameter Weibull distribution were estimated by simultaneous solution of maximum-likelihood equations for all conditioning data. In contrast to the experimental results given in the relevant literature, the estimates of the parameters were found to be dependent upon the pressure and geometry of the gap. The value of the shape parameter β≃7 seems to hold only for the conditioning data at 0.6 MPa. The lowest asymptotic value of the threshold estimator-minimum breakdown field strength was observed to be ~141 kV/cm