298 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS CHAPTER 7: PROTECTION
Transient Block Pickup Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.020 seconds
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 signal to
be passed and aligned with the indication specified by the
Ground Directional OC
Forward
setting for a period of time specified by the Transient Block Pickup Delay setting.
After this, the ground directional overcurrent path is virtually disabled for the time
specified by the
Transient Block Reset Delay setting.
When determining the delay to use, make it large enough to allow the selected ground
directional overcurrent function to operate, but not greater 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.
When determining the delay to use, take into account the value of the
RX Pickup Delay
setting. The POTT RX signal is shaped for aligning with the ground directional indication.
The original POTT RX signal is delayed by the value of the
RX Pickup Delay setting, then
terminated at the time specified by the
Transient Block Pickup Delay setting after the
pickup of the original POTT TX signal, and eventually locked-out for the time specified by
the
Transient Block Reset Delay setting.
Transient Block Reset Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.090 seconds
This setting specifies 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
Transient Block Pickup Delay setting). This delay needs to be
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 ensure that
the ground directional function is not jeopardized during delayed breaker operations.
Echo Duration
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.100 seconds
This setting specifies the guaranteed and exact duration of the echo pulse. The duration
does not depend on the duration and shape of the received RX signal. This setting
enables the relay to avoid a permanent lock-up of the transmit-receive loop.
Echo Lockout
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.250 seconds
This setting specifies the lockout period for the echo logic after sending the echo pulse.
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