The large oil gap and poor oil circulation in the ascending flanged base of large transformers may lead to delay in the transport of fault characteristic gases, making it difficult to detect a potential fault in time by the on-line or off-line dissolved gas analysis technology, which seriously endangers the safe operation of the transformer. A simulation model of the L-shaped ascending flanged base of the forced oil circulation transformer is established in ANSYS Fluent. Hydrogen was chosen as the representative species due to its highest diffusion coefficient among the fault gases. Using the finite element method, and considering the convection and diffusion processes, numerical simulations of the velocity distribution and hydrogen transport in the ascending flanged base were carried out. Results showed that the slow oil flow in the ascending flanged base impedes the transport of the fault gases. The H2 content at the port is more than two orders of magnitude smaller (lower than the alarming concentration) than that near the equalizing ball of high voltage bushing, which may lead to the failure in fault detection.

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