GE L60 Instruction Manual page 345

8 THEORY OF OPERATION 8.1 OVERVIEW
Figure 8–4: THREE-TERMINAL LINE PHASE COMPARISON
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Figure 8–5: SINGLE-PHASE COMPARISON BLOCKING SCHEME PRINCIPLE
It will be noted from Figure 8–5 that AND1 (the comparer) at each end of the line compares the coincidence time of the pos-
itive half cycle of current with the absence of receiver output. This is initiated only when a fault is present as indicated by an
output from FDH (Fault Detector High-set). FDH is set so that it does not pick up on load current but does pick up for all
faults on the protected line section. Thus, when a fault occurs, FDH picks up, and if the receiver output is not present for 3
milliseconds during the positive half cycle of current out of the mixing network, a trip output will be obtained.
GE Multilin L60 Line Phase Comparison Relay 8-5