GE L90 Instruction Manual page 382

5.7 CONTROL ELEMENTS
This scheme is intended for two-terminal line applications only. It uses an over-reaching zone 2 distance element to essen-
tially compare the direction to a fault at both the ends of the line. Ground directional overcurrent functions available in the
relay can be used in conjunction with the zone 2 distance element to key the scheme and initiate its operation. This pro-
vides increased coverage for high resistance faults.
For proper scheme operation, the zone 2 phase and ground distance elements must be enabled, configured, and set per
the 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 functions must be
enabled, configured, and set accordingly.
• POTT PERMISSIVE ECHO: If set to "Enabled" this setting will result in sending a permissive echo signal to the remote
end. The permissive signal is echoed back upon receiving a reliable
line-end-open condition is identified by the line pickup logic. The permissive echo is programmed as a one-shot logic.
The echo is sent only once and then the echo logic locks out for a settable period of time (
duration of the echo pulse does not depend on the duration or shape of the received
.
ECHO DURATION
• 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
delay will increase the response time of the scheme.
• TRANS BLOCK PICKUP DELAY: This setting defines a transient blocking mechanism embedded in the POTT
5
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
anism allows the
defined as
TRANS BLOCK PICKUP DELAY
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
POTT RX PICKUP DELAY
tion as follows: the original
after the pickup of the original
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
also the
TRANS BLOCK PICKUP DELAY
including not only current reversals but also spurious negative and zero-sequence currents occurring during breaker
operations. 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 jeopar-
dized 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
lock-up of the transmit/receive loop.
• ECHO LOCKOUT: This setting defines the lockout period for the echo logic after sending the echo pulse.
• LINE END OPEN PICKUP DELAY: This setting defines the pickup setting for validation of the line end open conditions
as detected by the Line Pickup logic through the
open condition is a requirement for the POTT scheme to return a received echo signal (if the echo feature is enabled).
The value of this setting should take into account the principle of operation and settings of the line pickup element.
5-246
POTT SCHEME TARGET:
MESSAGE
Self-Reset
POTT SCHEME EVENTS:
MESSAGE
Disabled
signal that can occur simultaneously with the zone 2 pickup. The selected
TX
signal to be passed and aligned with the
RX
. After that the ground directional overcurrent path will be virtually disabled for a
TRANS BLOCK RESET DELAY
should be long enough to give the selected ground directional overcurrent function
. The
POTT RX
signal is delayed by the
RX
signal, and eventually, locked-out for
POTT TX
). This delay should be selected long enough to cope with transient conditions
L90 Line Current Differential System
Range: Self-Reset, Latched, Disabled
Range: Disabled, Enabled
POTT RX
POTT RX
GND DIR O/C FWD
.
signal is shaped for aligning with the ground directional indica-
, then terminated at
POTT RX PICKUP DELAY
signal. This setting enables the relay to avoid a permanent
POTT RX
FlexLogic™ operand. The validated line end
LINE PICKUP LEO PKP
5 SETTINGS
signal from the remote end while the
setting). The
ECHO LOCKOUT
signal but is settable as
POTT RX
signal, the transient blocking mech-
indication only for a period of time
TRANS BLOCK PICKUP
TRANS BLOCK RESET DELAY
GE Multilin
.