4–94 889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUALINPUTS CHAPTER 4: SETPOINTSchange of state (mark no. 2 in the diagram). Once validated (debounced), the new state willbe declared and a FlexLogic operand will be asserted at the time of a new protection pass.A time stamp of the first sample in the sequence that validates the new state is used whenlogging the change of the Contact Input into the Event Recorder (mark no. 1 in thediagram).Protection and control elements, as well as FlexLogic equations and timers, are executedeight times in a power system cycle. The protection pass duration is controlled by thefrequency tracking mechanism. The FlexLogic operand reflecting the debounced state ofthe contact is updated at the protection pass following the debounce (marked no. 2 on thefigure below). The update is performed at the beginning of the protection pass so allprotection and control functions, as well as FlexLogic equations, are fed with the updatedstates of the Contact Inputs.The FlexLogic operand response time to the Contact Input change is related to thedebounce time setting plus up to one protection pass (variable and depending on systemfrequency if frequency tracking enabled). For example, 8 protection passes per cycle on a60 Hz system correspond to a protection pass every 2.1 ms. With a contact debounce timesetting of 3.0 ms, the FlexLogic™ operand-assert time limits are: 4.2 + 0.0 = 4.2 ms and 4.2+ 2.1 = 6.3 ms. The 4.2 ms is the minimum protection pass period that contains a debouncetime, 3.0 ms.Regardless of the contact debounce time setting, the Contact Input event is time-stampedwith 1 protection pass accuracy using the time of the first scan corresponding to the newstate (mark no. 1 below). Therefore, the time stamp reflects a change in the DC voltageacross the Contact Input terminals that was not accidental as it was subsequentlyvalidated using the debounce timer. The debounce algorithm is symmetrical: the sameprocedure and debounce time are used to filter the LOW-HIGH (marks no.1 and 2 in thefigure below) and HIGH-LOW (marks no. 3 and 4 below) transitions.Figure 4-27: Contact Input Debouncing Mechanism and Time-stamping Sample Timing
