CHAPTER 5: SETTINGS INPUTS/OUTPUTSC70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL 5-2935Protection and control elements, as well as FlexLogic equations and timers, are executed eight times in a power systemcycle. The protection pass duration is controlled by the frequency tracking mechanism. The FlexLogic operand reflectingthe debounced state of the contact is updated at the protection pass following the validation (marks no. 3 and 4 on thefigure that follows). The update is performed at the beginning of the protection pass so all protection and control functions,as well as FlexLogic equations, are fed with the updated states of the contact inputs.The FlexLogic operand response time to the contact input change is equal to the debounce time setting plus up to oneprotection pass (variable and depending on system frequency if frequency tracking enabled). If the change of state occursjust after a protection pass, the recognition is delayed until the subsequent protection pass; that is, by the entire durationof the protection pass. If the change occurs just prior to a protection pass, the state is recognized immediately. Statisticallya delay of half the protection pass is expected. Owing to the 0.5 ms scan rate, the time resolution for the input contact isbelow 1 ms.For example, eight protection passes per cycle on a 60 Hz system correspond to a protection pass every 2.1 ms. With acontact debounce time setting of 3.0 ms, the FlexLogic operand-assert time limits are: 3.0 + 0.0 = 3.0 ms and 3.0 + 2.1 = 5.1ms. These time limits depend on how soon the protection pass runs after the debouncing time.Regardless of the contact debounce time setting, the contact input event is time-stamped with a 1 μs accuracy using thetime of the first scan corresponding to the new state (mark no. 2 shown). Therefore, the time stamp reflects a change in theDC voltage across the contact input terminals that was not accidental as it was subsequently validated using thedebounce timer. Keep in mind that the associated FlexLogic operand is asserted/de-asserted later, after validating thechange.The debounce algorithm is symmetrical: the same procedure and debounce time are used to filter the LOW-HIGH (marksno.1, 2, 3, and 4 in the figure) and HIGH-LOW (marks no. 5, 6, 7, and 8) transitions.Figure 5-161: Input contact debouncing mechanism and time stamp sample timingContact inputs are isolated in groups of four to allow connection of wet contacts from different voltage sources for eachgroup. The CONTACT INPUT THRESHOLDS determine the minimum voltage required to detect a closed contact input. Thisvalue is selected according to the following criteria: 17 for 24 V sources, 33 for 48 V sources, 84 for 110 to 125 V sourcesand 166 for 250 V sources.For example, to use contact input H5a as a status input from the breaker 52b contact to seal-in the trip relay and record itin the Event Records menu, make the following settings changes:
