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Fig.1
Closed loop network configuration with RED615 line differential protection and control IEDs
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Fig. 2
Line differential protection of an overhead line feeder using RED615 with the standard configuration B. Selectivity of earth-fault protection is ensured using binary signal transfer (BST) between the directional E/F protection stages of the local and remote end. The lowest directional E/F stages are not used for tripping purposes,but set to detect earth-faults in the reverse direction. Upon detection of an out-of-zone earth-fault, a blocking signal is sent to the remote end directional E/F protection stage preventing tripping of the circuit breaker. If the earth-fault is within the protected zone, no blocking signal will be issued, and the internal fault is cleared by the tripping stages of the directional E/F protection. To ensure simultaneous tripping of the local and remote end circuit breakers, BST is also used for sending an intertrip signal to the remote end during earth-fault situations within the protected zone.
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Fig. 3
Line differential protection of an overhead line feeder using RED615 with the standard configuration C and auto-reclosing option. By means of binary signal transfer (BST) uncoordinated auto-reclosing attempts are prevented. During the autoreclosing sequence a “wait” command is sent to the auto-reclosing function of the lower circuit breaker and thereby blocking the function. The upper circuit breaker is thereafter closed by its auto-reclosing function. This blocking signal is reset after successful auto-reclosing of the upper circuit breaker, enabling the lower breaker to be closed by its auto-reclosing function.