5-392 D60 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUALCONTROL ELEMENTS CHAPTER 5: SETTINGS5The tripping or unblocking window for loss-of-guard without permission is the difference between the DCUB LOG TRIPWINDOW and DCUB LOG PICKUP DELAY timers. For the default settings, this difference is 150 – 8 = 142 ms and occurs 8 msafter loss-of-guard was received, when the DCUB LOG PICKUP DELAY timer has timed out. During this interval, the schemehas permission to operate if a forward fault is sensed, and no reverse faults or transient blocking.GUARD HEALTHY RESET DELAY — This setting represents the guard healthy security time delay. It is the time after the channelis restored that the guard signal must be present before the directional comparison unblocking scheme is put back inservice. This reset timer allows the scheme to ride through any chattering in the channel. Typical values are from 100 to500 ms, with a value of 150 ms commonly used.DCUB LOG TRIP WINDOW — This setting represents the directional comparison unblocking lockout time delay. It is theamount of time from when any loss-of-guard signal is received until the directional comparison unblocking scheme islocked out without the presence of any RX1 to RX4 receive signal or any forward element. This timer seals-in when itexpires, creating a blocking signal for all scheme functions and disabling the scheme until the guard signal is restored andthe GUARD HEALTHY RESET DELAY timer expires. Typical values for this setting are from 160 to 180 ms; for most cases, asetting of about 150 ms can be used.DCUB SEAL-IN DELAY — The output FlexLogic operand (DCUB OP) is produced according to the directional comparisonunblocking scheme logic. The DCUB SEAL-IN DELAY defines a minimum guaranteed duration of the DCUB OP pulse. As thisoperand runs the trip table of the directional comparison unblocking scheme, the DCUB TRIP A, DCUB TRIP B, DCUB TRIP C, andDCUB TRIP 3P trip operands are sealed-in for the same period of time.DCUB NO OF COMM BITS — This setting specifies the number of bits available on the communications channel for thescheme. With only one bit available, the scheme sends the direct under-reaching transfer trip command on bit 1 (DCUB TX1operand) and responds to the direct trip command received on bit 1 (DCUB RX1 setting). The scheme uses only local faulttype identification provided by the phase selector to assert the DCUB TRIP A, DCUB TRIP B, DCUB TRIP C, and DCUB TRIP 3Poutput operands.DCUB RX1 through DCUB RX4 — These settings allow the user to select the FlexLogic operands to represent the permissionreceive signals for the scheme. Contact inputs interfacing with a signaling system(s) are typically used. These settings mustbe used in conjunction with the loss-of-guard signals, otherwise the scheme does not unblock and thus fails to operate.In single-bit applications, DCUB RX1 must be used. In two-bit applications, DCUB RX1 and DCUB RX2 must be used. In four-bitapplications, DCUB RX1, DCUB RX2, DCUB RX3, and DCUB RX4 must be used.DCUB LOG1 through DCUB LOG4 — These settings allow the user to select the FlexLogic operands to represent the loss-of-guard receive signals for the scheme. Contact inputs interfacing with a signaling system(s) are typically used. Each loss-of-guard signal must correspond to the same receive signal from the same communications channel (that is, RX1 and LOG1must be from the same communications channel, and the same for channels 2, 3 and 4, if used).In single-bit applications, DCUB RX1 and DCUB LOG1 must be used. In two-bit applications, DCUB RX1 with DCUB LOG1 andDCUB RX2 with DCUB LOG2 must be used. In four-bit applications, all receive and loss-of-guard signals must be used.
