GE L90 Instruction Manual page 270

5.6 CONTROL ELEMENTS
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 RX signal is delayed by the
after the pickup of the original POTT TX signal, and eventually, locked-out for
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 POTT RX signal. This setting enables the relay to avoid a perma-
nent 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 LINE PICKUP LEO PKP FlexLogic™ operand. The validated line end
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
5
element.
• POTT SEAL-IN DELAY: The output FlexLogic™ operand (POTT OP) is produced according to the POTT scheme
logic. A seal-in time delay is applied to this operand for coping with noisy communication channels. The POTT SEAL-
IN DELAY defines a minimum guaranteed duration of the POTT OP pulse.
• 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 keying the communication channel and initiating opera-
tion 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
the user to combine responses of various protection elements, or to apply extra conditions through FlexLogic™ equa-
tions, this extra signal is primarily meant to be the output operand from either the Negative-Sequence Directional IOC
or Neutral Directional IOC. Both of these elements have separate forward (FWD) and reverse (REV) output operands.
The forward indication should be used (
• POTT RX: This setting enables the user to select the FlexLogic™ operand that represents the receive signal (RX) for
the scheme. Typically an input contact interfacing with a signaling system is used. Other choices include Remote
Inputs and FlexLogic™ equations. The POTT transmit signal (TX) should be appropriately interfaced with the signaling
system by assigning the output FlexLogic™ operand (POTT TX) to an output contact. The Remote Output mechanism
is another choice.
The output operand from the scheme (POTT OP) must be configured to interface with other relay functions, output
contacts in particular, in order to make the scheme fully operational. Typically, the output operand should be pro-
grammed to initiate a trip, breaker fail, and autoreclose, and drive a user-programmable LED as per user application.
5-180
. 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 shaped for aligning with the ground directional indica-
POTT RX PICKUP DELAY
). This delay should be selected long enough to cope with transient conditions
. Even though any FlexLogic™ operand could be used as
NEG SEQ DIR OC1 FWD
L90 Line Differential Relay
, then terminated at
TRANS BLOCK RESET DELAY
or ).
NEUTRAL DIR OC1 FWD
5 SETTINGS
TRANS BLOCK PICKUP
.
allowing
GND DIR O/C FWD
GE Multilin