Weibull parameter of oil-immersed transformer to evaluate insulation reliability on temporary overvoltage

In the condition settings of a power-frequency withstand voltage test for substation equipment, an approach based on the insulation reliability evaluation using Weibull distribution is available. However, the issue to be discussed remains in this approach. For example, temporary overvoltage during the operation is evaluated through Weibull-distribution parameters obtained from an experiment without operating voltage. For an oil-immersed transformer, the breakdown voltage-time (V-t) characteristics of the oil gap were obtained as basic characteristics in the previous experiment. It was experimented with 0 cm/s, 8cm/s and 16cm/s oil flow velocity as a parameter affecting the voltage application history. In this paper, an insulation characteristic was obtained in a pattern of voltage application assuming temporary overvoltage during operation. The results were compared with the basic characteristics in the previous experiment, and insulation reliability was calculated in trial. Consequently, the insulation reliability evaluation based on the existing V-t characteristic test parameters was found to be practically on the safe side and appropriate.