9-32 L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUALOVERVIEW CHAPTER 9: THEORY OF OPERATION9Figure 9-23: Dual-breaker logic for permissive and blocking transmit schemesFor tripping (permissive) schemes, a positive polarity is declared for the terminal if one breaker displays positive polaritywhen 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 ofthe two breakers sees a reverse direction. It must be kept in mind that the positive and negative pulses do not necessarilycomplement each other, and therefore, one must not substitute not(positive polarity) = negative polarity.
