| 摘要 |
In a three terminal power line current differential protection system, all three phase current values (IA, IB and IC) are obtained from all three terminals. The current values for each phase are processed in three successive processing operations, using in turn the current values from each terminal as local current values and the combination of the other two terminal current values in each case as the remote current values. The resulting local and remote current values are then processed against pre-selected values which establish a restrain region in the current ratio (alpha) plane. Current values for each set of local and combined remote currents which result in the ratio being within the restrain region result in a blocking signal while current values which result in a ratio outside of the region result in a tripping signal. If the outputs of the three processing operations agree, then that signal is the system output. If there is disagreement, the output produced when the terminal having the largest current (Imax) value is the local current is the system output.
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