GE D90 Plus Instruction Manual page 323

CHAPTER 7: PROTECTION
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
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 is delayed
unnecessarily.
Make this setting less than the fastest possible trip time for faults on an adjacent line so
that extended blocking action can be established. 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, do not make the delay defined
by this setting 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).
Delay
Make this delay 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). Consider the breaker failure time of the
surrounding protection systems within the reach of the ground directional function used
by the directional comparison unblocking scheme, 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).
When determining the delay value, take into account the principle of operation and
settings of the line pickup element, which needs to 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
to cope with evolving faults when an external
Transient Block Pickup
operand. The validated line
LINE PICKUP LEO PKP
CONTROL ELEMENTS
313