GE L90, Инструкция по эксплуатации

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5-396 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS CHAPTER 5: SETTINGS
5
GND DIR O/C REV
— This setting defines 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 set as
GND DIR O/C REV
. Even
though any FlexLogic operand can be set as
GND DIR O/C REV
, 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 (that is,
NEG SEQ DIR OC1 REV
or
NEUTRAL DIR OC1 REV
).
Coordinate the selected protection element (or elements in combination) with the selection of
GND DIR O/C FWD
. For all the
forward external faults seen by an element set as
GND DIR O/C FWD
at one end of the line, the reverse-looking element set
as
GND DIR O/C REV
at the other end picks up and provides a blocking signal. For greater security and to overcome spurious
directional element operation during transients, adding a pickup delay greater than the pilot channel delay to the reverse
directional element is recommended.
TRANS BLOCK PICKUP DELAY
— This setting defines 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
TRANS BLOCK
PICKUP DELAY
value, the blocking operation is extended by the transient blocking timer for the
TRANS BLOCK RESET DELAY
value. This allows riding through current reversal conditions.
However, if distance zone 1 picks up during the transient blocking condition, the blocking action is removed. This is to cope
with evolving faults when an external fault is followed by an internal fault. Without the zone 1 feedback, the trip is delayed
unnecessarily.
Do not set the
TRANS BLOCK PICKUP DELAY
longer 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 set
the delay defined by this setting too short.
TRANS BLOCK RESET DELAY
— This setting defines 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 previous
TRANS BLOCK PICKUP DELAY
setting).
Set 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
— This setting defines 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
— This setting defines 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
— This setting defines the pickup value for validation of the line end open conditions as
detected by the line pickup logic via the
LINE PICKUP LEO PKP
FlexLogic operand. The validated line 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 selecting this delay value, take into account the principle of operation and settings of the line pickup element, which
should thus be enabled.
DCUB LOG PICKUP DELAY
— This setting represents the directional comparison unblocking duration time delay. It 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 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 setting values are
from 4 to 32 ms. For most cases, a value of 8 ms can be used.