In the pilot channel blocking scheme a fault inception detected by a fast acting change
detector is used to send a block signal to the remote end in order to block an overreaching
zone. If the fault is later detected as a forward fault the earlier sent blocking signal is
stopped.
The blocking scheme is very dependable because it will operate for faults anywhere on the
protected line if the communication channel is out of service. Conversely, it is less secure
than permissive schemes because it will trip for external faults within the reach of the
tripping function if the communication channel is out of service. Inadequate speed or
dependability can cause spurious tripping for external faults. Inadequate security can
cause delayed tripping for internal faults.
ZSMGAPC function also includes functionality for blocking the sample based distance
protection due to high SIR. SIR directly influences the fault voltage level for a given
voltage level, and this is the major factor that affects the severity of CVT transients.
Therefore, in cases where the SIR value is too high, further filtering of the measured
signals will be needed.
8.7.3 Setting guidelines
GlobalBaseSel: Selects the global base value group used by the function to define IBase,
VBase and SBase as applicable.
PilotMode: Set PilotMode to On when pilot scheme is to be used. In this mode fault
inception function will send a block signal to remote end to block the overreaching zones,
when operated.
DeltaI: The setting of DeltaI for fault inception detection is by default set to 10% of
IBase, which is suitable in most cases.
Delta3I0: The setting of the parameter Delta3I0 for fault inception detection is by default
set to 10% of VBase, which is suitable in most cases.
DeltaV: The setting of DeltaV for fault inception detection is by default set to 5% of
IBase, which is suitable in most cases.
Delta3V0: The setting of Delta3V0 for fault inception detection is by default set to 5% of
VBase, which is suitable in most cases.
Zreach: The setting of Zreach must be adopted to the specific application. The setting is
used in the SIR calculation for detection of high SIR.
SIRLevel: The setting of the parameter SIRLevel is by default set to 10. This is a suitable
setting for applications with CVT to avoid transient overreach due to the CVT dynamics.
If magnetic voltage transformers are used, set SIRLevel to 15 the highest level.
Section 8 1MRK 506 369-UUS -
Impedance protection
304 Line distance protection REL670 2.2 ANSI
Application manual
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