CHAPTER 7: PROTECTION
CONTROL ELEMENTS
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
295
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 will be virtually disabled for the time
specified by the
Transient Block Reset Delay
setting.
The
Transient Block Pickup Delay
setting should be 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.
This setting should 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 should 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 may 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.
