312 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS CHAPTER 7: PROTECTION
Ground Directional OC Forward
Range: any FlexLogic operand
Default: OFF
This setting selects the FlexLogic operand (if any) of a protection element used in
addition to zone 2 for identifying faults on the protected line, and thus, for keying the
communication channels and initiating operation of the scheme (both through the
transient blocking logic).
Good directional integrity is the key requirement for an over-reaching forward-looking
protection element selected with this setting. Even though any operand can be selected
for this feature, thereby enabling the user to combine responses of various protection
elements or to apply extra conditions through FlexLogic equations, this extra signal is
primarily meant to be the output operand from either the negative-sequence directional
or neutral directional overcurrent elements. As both these elements have separate
forward and reverse output operands, use the forward indication (that is, NEG SEQ DIR OC1
FWD or NEUTRAL DIR OC1 FWD).
Coordinate the selected protection element (or elements in combination) with this
setting. For all forward external faults seen by an element set by the
Ground Directional
OC Forward setting at one end of the line, the reverse-looking element set by the Ground
Directional OC Reverse setting at the other end picks up and provides a blocking signal.
Ground Directional OC Reverse
Range: any FlexLogic operand
Default: OFF
This setting selects the FlexLogic operand (if any) of a protection element used in
addition to zone 4 for identifying reverse faults, and thus, for stopping the transmit
signal and initiating the transient blocking timer.
Good directional integrity is the key requirement for a reverse-looking protection
element selected by this setting. Even though any operand can be selected, thereby
enabling the user to combine responses of various protection elements or to apply extra
conditions through FlexLogic equations, this extra signal is primarily meant to be the
output operand from either the negative-sequence directional or neutral directional
overcurrent element. As both these elements have separate forward and reverse output
operands, use the reverse indication (NEG SEQ DIR OC1 REV or NEUTRAL DIR OC1 REV).
Coordinate the selected protection element (or elements in combination) with the
Ground Directional OC Forward setting. For all the forward external faults seen by an
element set by the
Ground Directional OC Forward setting at one end of the line, the
reverse-looking element set as the
Ground Directional OC Reverse setting at the other
end picks up and provides a blocking signal.
Transient Block Pickup Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.020 seconds
This setting specifies a transient blocking mechanism embedded in the directional
comparison unblocking scheme for coping with the exposure of both the over-reaching
zone 2 and ground directional overcurrent function to current reversal conditions.
The transient blocking logic applies to both operate (trip) and send (transmit) paths.
Identifying the fault as a reverse fault prevents the scheme from both operating and
keying the channel. If the reverse fault condition prevails for the time specified by this
setting, the blocking operation is extended by the transient blocking time specified by
the
Transient Block Reset Delay setting. This allows riding through current reversal
conditions.
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