GE D90 Plus Instruction Manual page 278

CONTROL ELEMENTS
270
However, if distance zone 1 picks up during the transient blocking condition, the blocking
action is removed. This allows the D90
fault is followed by an internal fault. Without the zone 1 feedback, the trip would be
unnecessarily delayed.
This setting should not be greater than the fastest possible trip time for faults on an
adjacent line so that extended blocking action could be established. This should take
into account the pickup time of the reverse-looking elements of the scheme. To avoid
locking up a spurious reverse fault indication that can occur during internal fault
conditions, the delay defined by this setting should not be too short.
Transient Block Reset Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.090 seconds
This setting specifies a transient blocking mechanism embedded in the directional
comparison unblocking scheme for coping with the exposure of the overreaching
protection functions to current reversal conditions (see also the
setting above).
Delay
This delay should be long enough to cope with transient conditions including not only
current reversals but also spurious negative and zero-sequence currents occurring
during breaker operations (in the case when neutral directional or negative-sequence
directional overcurrent functions are used). The breaker failure time of the surrounding
protection systems within the reach of the ground directional function used by the
directional comparison unblocking scheme should be considered to make sure that the
ground directional function is not jeopardized during delayed breaker operations.
Echo Duration
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.100 seconds
This setting specifies the guaranteed and exact duration of the echo pulse. The duration
does not depend on the duration and shape of the received RX signals. This setting
enables the relay to avoid a permanent lock-up of the transmit-receive loop.
Echo Lockout
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.250 seconds
This setting specifies the lockout period for the echo logic after sending the echo pulse.
This setting enables the relay to avoid oscillations of the echo pulses during an
autoreclosure dead-time after clearing an internal fault.
Line End Open Pickup Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.050 seconds
This setting specifies the pickup value for validation of the line end open conditions as
detected by the line pickup logic via the
end open condition is a requirement for the directional comparison unblocking scheme
to return a received echo signal (if the echo feature is enabled).
The value of this setting should take into account the principle of operation and settings
of the line pickup element, which should thus be enabled.
Loss of Guard Pickup Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.008 seconds
This setting specifies the directional comparison unblocking duration time delay. This is
the amount of time that the loss-of-guard without receipt of permissive trip must be
present before the logic provides permission to operate if a forward fault is detected. It is
Plus
cope with evolving faults when an external
LINE PICKUP LEO PKP
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION
Transient Block Pickup
operand. The validated line