GE L90 Instruction Manual page 420

5.7 CONTROL ELEMENTS
For proper operation, the Zone 2 phase and ground distance elements must be enabled, configured and set per rules of
distance relaying. The Line Pickup element should be enabled, configured and set properly to detect line-end-open/weak-
infeed conditions. If used by this scheme, the selected ground directional overcurrent function(s) must be enabled, config-
ured and set accordingly.
In single-pole tripping applications, the scheme uses local fault type identification provided by the Phase Selector together
with information received from the remote terminal. The scheme generates output operands (
that are used to transmit the signal to the remote end. Choices of communications channel include remote inputs/outputs
and telecommunications interfaces. When used with telecommunications facilities the output operands should be assigned
to operate output contacts connected to assert the individual bits at the interface.
To make the scheme fully operational as a stand-alone feature, the scheme output operands must be configured to inter-
face with other relay functions, output contacts in particular. Typically, the output operands should be programmed to initiate
a trip, breaker fail, and autoreclose, and drive a user-programmable LED as per user application.
When used in conjunction with the Trip Output element, the scheme is pre-configured to initiate trip, breaker fail, and single-
pole autoreclose actions.
• POTT SCHEME BLOCK: This setting allows the user to assign any FlexLogic operand to block the scheme. Contact
inputs from a pilot cut-out switch are typically used for this purpose.
• POTT PERMISSIVE ECHO: If this setting is set to "Enabled", the scheme sends a permissive echo signal to the
remote end(s) using a pre-programmed logic (see the following logic diagram). If set to "Custom", the echo signal is
sent if a condition selected via the
locks out for the time specified by the
Operation of the overreaching protection elements (Distance Zone 2 or
• POTT ECHO COND: This setting specifies a user-selected echo condition and applies only if the
is set to "Custom".
SIVE ECHO
5
• POTT RX PICKUP DELAY: This setting enables the relay to cope with spurious receive signals. The delay should be
set longer than the longest spurious
selected delay will increase the response time of the scheme.
• TRANS BLOCK PICKUP DELAY: This setting defines a transient blocking mechanism embedded in the POTT
scheme for coping with the exposure of a ground directional overcurrent function (if used) to current reversal condi-
tions. The transient blocking mechanism applies to the ground overcurrent path only as the reach settings for the Zone
2 distance functions is not expected to be long for two-terminal applications, and the security of the distance functions
is not endangered by the current reversal conditions.
Upon receiving the
with the
GND DIR O/C FWD
directional overcurrent path will be virtually disabled for a period of time specified as
The
TRANS BLOCK PICKUP DELAY
time to operate, but not longer than the fastest possible operation time of the protection system that can create current
reversal conditions within the reach of the selected ground directional overcurrent function.
This setting should take into account the
ground directional indication as follows: the original RX signal is delayed by the
at
TRANS BLOCK PICKUP DELAY
BLOCK RESET DELAY
• TRANS BLOCK RESET DELAY: This setting defines a transient blocking mechanism embedded in the POTT scheme
for coping with the exposure of a ground directional overcurrent function (if used) to current reversal conditions (see
the
TRANS BLOCK PICKUP DELAY
ing not only current reversals but also spurious negative- and zero-sequence currents occurring during breaker opera-
tions. The breaker failure time of the surrounding protection systems within the reach of the ground directional function
used by the POTT scheme may be considered to make sure that the ground directional function is not jeopardized dur-
ing 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
up of the transmit/receive loop.
• ECHO LOCKOUT: This setting defines the lockout period for the echo logic after sending the echo pulse.
5-290
POTT ECHO COND
ECHO LOCKOUT
signal that can be received simultaneously with the Zone 2 pickup. The
TX
signal, the transient blocking mechanism allows the
POTT RX
indication only for a period of time set by
should be long enough to give the selected ground directional overcurrent function
POTT RX PICKUP DELAY
after the pickup of the original
.
). This delay should be selected long enough to cope with transient conditions includ-
L90 Line Current Differential System
setting is satisfied. The echo is sent only once and then the logic
. The duration of the echo pulse is settable as
GND DIR O/C FWD
TRANS BLOCK PICKUP DELAY
. The
POTT RX
POTT RX PICKUP DELAY
signal, and eventually locked-out for
POTT TX
signal. This setting enables the relay to avoid a permanent lock-
RX
5 SETTINGS
through
POTT TX1 POTT TX4
ECHO DURATION
setting) inhibits the echo.
HYB POTT PERMIS-
signal to be passed and aligned
RX
. After that the ground
TRANS BLOCK RESET DELAY
signal is shaped for aligning with the
, then terminated
GE Multilin
)
.
.
TRANS