Importance

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Abstract

Direct transfer trip apparatus for sharing a common active communication channel utilized for signal transfer between at least two electromechanical units which form a current differential protective relay for protecting at least one power line in a power system network is disclosed. Each electromechanical unit includes an operating relay coil for effecting an interruption of current through the protected power line when an internal fault of the power line is detected. The direct transfer trip function induces signals to be transmitted through the common active communication channel either upstream or downstream from a faulted power line section where a breaker has failed to open. These direct transfer trip signals are supplied directly to an upstream or downstream breaker unit to operate the breaker to interrupt current through the faulted section independent of the energization of its corresponding operating relay coil. The direct transfer trip apparatus not only performs the aforementioned direct transfer trip function, but also permits disabling of the operating relay coil from effecting a power line interruption inadvertently. Accordingly, an inadvertent current interruption of the power line section by a corresponding operating relay coil is precluded during the transmission of the direct transfer trip signal over the common active communication channel.

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First Claim