5-390
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS
CHAPTER 5: SETTINGS
5
BLOCK RX CO-ORD PKP DELAY
— This setting defines a delay for the forward-looking protection elements used by the
scheme for coordination with the blocking response from the remote end(s). In this setting, include both the response time
of the protection elements used to establish a blocking signal and the total transmission time of that signal including the
relay communications equipment interfacing and the communications channel itself.
TRANS BLOCK PICKUP DELAY
— This setting defines a transient blocking mechanism embedded in the blocking 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 the send path only. Identifying the fault as a reverse fault establishes the blocking
signal. If the reverse fault condition prevails for
TRANS BLOCK PICKUP DELAY
, the blocking operation is extended by the
transient blocking timer for
TRANS BLOCK RESET DELAY
. This allows riding through current reversal conditions. However, if
zone 1 picks up during the transient blocking condition, the blocking action is removed. This is done to cope with evolving
faults when an external fault is followed by an internal fault. Without the zone 1 feedback, the trip is unnecessarily
delayed.
Do not set the
TRANS BLOCK PICKUP DELAY
longer than the fastest possible trip time for faults on an adjacent line so that the
extended blocking action can be established. Take into account the pickup time of the reverse-looking elements of the
scheme. Do not set the delay too short, in order to avoid locking up a spurious reverse fault indication that can occur
during internal fault conditions.
TRANS BLOCK RESET DELAY
— This setting defines a transient blocking mechanism embedded in the blocking scheme for
coping with the exposure of the overreaching protection functions to current reversal conditions (see also the
TRANS BLOCK
PICKUP DELAY
).
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 breaker failure time of the surrounding protection systems
within the reach of the ground directional function used by the blocking scheme, to make sure that the ground directional
function is not jeopardized during delayed breaker operations.
BLOCK SCHEME SEAL-IN DELAY
— The output FlexLogic operand (
DIR BLOCK OP
) is produced according to the Blocking scheme
logic. The
BLOCK SCHEME SEAL-IN DELAY
defines a minimum guaranteed duration of the
DIR BLOCK OP
pulse. As this operand
runs the Trip Table of the Blocking scheme, the trip operands
DIR BLOCK TRIP A
,
B
,
C
, and
3P
are sealed-in for the same period
of time.
GND DIR O/C FWD
— This setting defines 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 initiating operation of the scheme. Good directional integrity is the key
requirement for an over-reaching forward-looking protection element used as
GND DIR O/C FWD
.
Even though any FlexLogic operand can be used as
GND DIR O/C FWD
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. Both these
elements have separate forward (
FWD
) and reverse (
REV
) output operands.
The forward indication is used (
NEG SEQ DIR OC1 FWD
or
NEUTRAL DIR OC1 FWD
). Coordinate the selected protection element
(or elements in combination) with the selection of G
ND DIR O/C REV
. For all the forward external faults seen by an element
used as
GND DIR O/C FWD
at one end of the line, the reverse-looking element used 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 at least 0.5 cycles of pickup delay to the forward directional element is recommended.
GND DIR O/C REV
— This setting defines the FlexLogic operand (if any) of a protection element that is used in addition to
zone 4 for identifying reverse faults, and thus, for initiating the blocking signal. Either reverse-looking directional or non-
directional overcurrent protection element can be used as
GND DIR O/C REV
.
Even though any FlexLogic operand can be used as
GND DIR O/C REV
, 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, neutral directional, or a non-directional instantaneous
overcurrent element.
