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D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
POWER SYSTEM
CHAPTER 7: PROTECTION
Ground CT Secondary
Range: 1 A, 5 A
Default: 5 A
This setting selects the ground CT secondary value. It is used to derive secondary current
values from per-unit settings used in protection elements.
Current Cutoff Level
Range: 0.002 to 0.020 pu in steps of 0.001
Default: 0.020 pu
This setting modifies the current cut-off threshold. Very low currents (1 to 2% of the
rated value) are very susceptible to noise. Some customers prefer very low currents to
display as zero, while others prefer the current be displayed even when the value reflects
noise rather than the actual signal. The D90
Plus
applies a cut-off value to the magnitudes
and angles of the measured currents. If the magnitude is below the cut-off level, it is
substituted with zero. This applies to phase and ground current phasors as well as true
RMS values and symmetrical components. The cut-off operation applies to quantities
used for metering, protection, and control, as well as those used by communications
protocols. Raw current samples available via oscillography are not subject to cut-off.
NOTE
NOTE:
Lower the
Current Cutoff Level
setting with care as the D90
Plus
accepts lower signals as
valid measurements. Unless dictated otherwise by a specific application, the default
setting of “0.020 pu” is recommended.
Voltage inputs
Select the
Settings > Protection > Power System > AC Inputs - Voltage
menu item to
open the voltage input configuration window.
Figure 152: Voltage input configuration settings
This menu allows the user to specify the parameters for each voltage input. The
Phase VT
Ratio
and
Auxiliary VT Ratio
settings are used for calculation of primary metering values or
matching primary voltage in a synchrocheck application. The
Phase VT Secondary
and
Auxiliary VT Secondary
settings are used to derive secondary voltage values from the per-
unit settings used in protection elements. Protection functions that require phase-to-
neutral or zero-sequence quantities will not function correctly for delta VT configurations.
The following voltage input settings are available.
Phase VT Connection
Range: Wye, Delta
Default: Wye
This setting specifies the phase VT connection type for the corresponding voltage input.
An open-delta source VT connection would be entered as “Delta”.