314 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM ā INSTRUCTION MANUAL
CONTROL ELEMENTS CHAPTER 7: PROTECTION
set relatively short, but long enough to ride through the transition period of loss-of-
guard with the receipt of a permissive signal that occurs with a normal trip. Typical
settings are from 4 to 32 ms. For most cases, a value of 8 ms can be used.
The tripping or unblocking window for loss-of-guard without permission is the difference
between the timers specified by the
Loss of Guard Trip Window and Loss of Guard Pickup
delay settings. For the default settings, this difference is 150 ā 8 = 142 ms and occurs
8 ms after loss-of-guard was received, when the timer specified by this setting has timed
out. During this interval, the scheme has permission to operate if a forward fault is
sensed, and no reverse faults or transient blocking.
Guard Healthy Reset Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.015 seconds
This setting specifies the guard healthy security time delay. This is the time after the
channel is restored that the guard signal must be present before the directional
comparison unblocking scheme is put back in service. This reset timer allows the
scheme to ride through any chattering in the channel. Typical values are from 100 to
500 ms, with 150 ms commonly used.
Loss of Guard Trip Window
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.015 seconds
This setting specifies the directional comparison unblocking lockout time delay. This is
the amount of time from when any loss-of-guard signal is received until the directional
comparison unblocking scheme is locked out without the presence of any RX1 to RX4
receive signal or any forward element. This timer seals-in when it expires, creating a
blocking signal for all scheme functions and disabling the scheme until the guard signal
is restored and the timer specified by the
Guard Healthy Reset Delay setting expires.
Typical values for this setting are from 160 to 180 ms; for most cases, a setting of about
150 ms can be used.
Seal-In Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.010 seconds
The DCUB OP output operand is produced according to the directional comparison
unblocking scheme logic. This setting specifies a minimum guaranteed duration for the
DCUB OP pulse. As this operand runs the trip table of the directional comparison
unblocking scheme, the DCUB TRIP A, DCUB TRIP B, DCUB TRIP C, and DCUB TRIP 3P trip
operands are sealed-in for the same period of time.
Communication Bits
Range: 1, 2, 4
Default: 1
This setting specifies the number of bits available on the communications channel for
the scheme. With only one bit available, the scheme sends the direct under-reaching
transfer trip command on bit 1 (via the DCUB TX1 operand) and responds to the direct trip
command received on bit 1 (
RX1 setting). The scheme uses only local fault type
identification provided by the phase selector to assert the DCUB TRIP A, DCUB TRIP B, DCUB
TRIP C, and DCUB TRIP 3P output operands.
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