CHAPTER 5: SETTINGS
CONTROL ELEMENTS
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
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5
current reversal conditions. Upon receiving the
POTT RX
signal, the transient blocking mechanism allows the
RX
signal to be
passed and aligned with the
GND DIR O/C FWD
indication only for a period of time defined as
TRANS BLOCK PICKUP DELAY
.
After that the ground directional overcurrent path is virtually disabled for a period of time specified as
TRANS BLOCK RESET
DELAY
.
Set the
TRANS BLOCK PICKUP DELAY
long enough to give the selected ground directional overcurrent function 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. For this setting, also take into account
the
POTT RX PICKUP DELAY
. The
POTT RX
signal is shaped for aligning with the ground directional indication as follows: the
original
RX
signal is delayed by the
POTT RX PICKUP DELAY
, then terminated at
TRANS BLOCK PICKUP DELAY
after the pickup 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
). 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. The breaker failure
time of the surrounding protection systems within the reach of the ground directional function used by the POTT scheme
can be considered to make sure that the ground directional function is not jeopardized 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 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). Also for this setting,
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. This setting specifies a minimum
guaranteed duration of the
POTT OP
pulse.
GND DIR O/C FWD
— This setting selects 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 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
allowing 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 overcurrent or neutral directional
overcurrent elements. Both of these elements have separate forward and reverse output operands. The forward indication
should be used (
NEG SEQ DIR OC1 FWD
or
NEUTRAL DIR OC1 FWD
). 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.
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 programmed to initiate
a trip, breaker fail, and autoreclose, and drive a user-programmable LED as per user application.
