Recently, the operation of a mixed transmission system has increased due to rapid urbanization and the purpose of a good view. Therefore, a proper protection scheme for a mixed transmission system is required. Generally, when a fault occurs on a transmission line, auto reclosing is performed for the purpose of improving the continuity of service by clearing the fault and restoring the power system. However, the auto reclosing scheme should be applied to a mixed transmission system carefully because the mixed transmission system involves underground cable sections. When a fault occurs in the underground cable section, it is mostly a permanent fault. If auto reclosing is performed on a permanent fault condition, it may cause excessive overcurrent and switching surge, which can generate a serious impact on the whole transmission system and even cause an explosion. Due to this, many utilities worldwide do not allow auto reclosing or only apply it very restrictively on a mixed transmission system based on their practice. However, there is no clear guidance or standard related to auto reclosing on a mixed transmission system. Therefore, in this paper, an application of a recloser operation algorithm is proposed. Based on the proposed algorithm, reclosers can work properly and protect the transmission system. To verify the proposed algorithm, simulations were conducted using the ElectroMagnetic Transient Program (EMTP).
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