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L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
OVERVIEW
CHAPTER 9: THEORY OF OPERATION
9
Figure 9-23: Dual-breaker logic for permissive and blocking transmit schemes
For tripping (permissive) schemes, a positive polarity is declared for the terminal if one breaker displays positive polarity
when its FDL flag is set, while the other breaker either does not show the negative polarity or its FDL flag is dropped out.
The transmission logic for the blocking follows a different reasoning. Here, a blocking action must be established if any of
the two breakers sees a reverse direction. It must be kept in mind that the positive and negative pulses do not necessarily
complement each other, and therefore, one must not substitute not(positive polarity) = negative polarity.