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GE UR Series Instruction Manual Page 233

Line differential relay.
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5 SETTINGS
5.6 CONTROL ELEMENTS
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 conditions. 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 POTT RX signal, the transient blocking mechanism allows the RX signal to be passed and aligned with
the
indication only for a period of time defined as
. After that the ground direc-
GND DIR O/C FWD
TRANS BLOCK PICKUP DELAY
tional overcurrent path will be virtually disabled for a period of time specified as
.
TRANS BLOCK RESET DELAY
The
should be long enough to give the selected ground directional overcurrent function time to
TRANS BLOCK PICKUP DELAY
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
. The POTT RX signal is shaped for aligning with the ground directional indication as follows: The
POTT RX PICKUP DELAY
original RX signal is delayed by the
, then terminated at
after the pickup
POTT RX PICKUP DELAY
TRANS BLOCK PICKUP DELAY
of the original POTT TX signal, and eventually, locked-out for
.
TRANS 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 also the
).
TRANS BLOCK PICKUP DELAY
This delay should be selected long enough to cope with transient conditions including not only current reversals but also
spurious negative- and zero-sequence currents occurring during breaker operations. The breaker failure time of the sur-
rounding protection systems within the reach of the ground directional function used by the POTT scheme may be consid-
ered to make sure that the ground directional function is not jeopardized during delayed breaker operations.
ECHO DURATION:
5
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 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.
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 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 operation of the scheme. Good direc-
tional 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 could be used as
allowing the user to combine responses of vari-
GND DIR O/C FWD
ous 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 IOC or Neutral Directional IOC. Both of these ele-
ments have separate forward (FWD) and reverse (REV) output operands. The forward indication should be used (
NEG SEQ
or
).
DIR OC1 FWD
NEUTRAL DIR OC1 FWD
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.
GE Power Management
L90 Line Differential Relay
5-149

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