CHAPTER 7: PROTECTION
POWER SYSTEM
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
173
Phase VT Secondary
Range: 50.0 to 240.0 volts in steps of 0.1
Default: 66.4 volts
This setting specifies the nominal phase VT voltage for the corresponding voltage input.
It is typically used to derive secondary voltage values from the per-unit settings used in
protection elements.
The typical
Phase VT Secondary
setting is the phase-to-phase secondary voltage
appearing at the relay input terminals when nominal voltage is applied to the VT
primary. For example, on a system with a 13.8 kV nominal primary voltage and with a
14400:120 V VT in a delta connection, the secondary voltage is (13800 V / 14400) × 120 =
115 V. Thus, the
Phase VT Secondary
setting would be 115 volts.
Phase VT Ratio
Range: 1.00 to 24000.00 in steps of 0.01
Default: 1.00
This setting specifies the phase VT ratio for the corresponding voltage input. It is
typically used for calculation of primary metering values or matching primary voltage in
a synchrocheck application.
Auxiliary VT Connection
Range: Vag, Vbg, Vcg, Vab, Vbc, Vca, Vn
Default: Vag
This setting specifies the auxiliary VT connection type for the corresponding voltage
input.
Auxiliary VT Secondary
Range: 50.0 to 240.0 volts in steps of 0.1
Default: 66.4 volts
This setting specifies the nominal auxiliary VT voltage for the corresponding voltage
input. It is typically used to derive secondary voltage values from the per-unit settings
used in protection elements.
Auxiliary VT Ratio
Range: 1.00 to 2400.00 in steps of 0.001
Default:
This setting specifies the auxiliary VT ratio for the corresponding voltage input. It is
typically used for calculation of primary metering values or matching primary voltage in
a synchrocheck application.
Voltage Cutoff Level
Range: 0.1 to 1.0 volts secondary in steps of 0.1
Default: 1.0 volts secondary
This setting specifies the voltage cut-off threshold. Very low secondary voltage
measurements (at the fractional volt level) can be affected by noise. Some customers
prefer these low voltages to be displayed as zero, while others prefer the voltage to 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 voltages.
If the magnitude is below the cut-off level, it is substituted with zero. This operation
applies to phase voltages, auxiliary voltages, 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 samples of the voltages available via
oscillography are not subject cut-off.
NOTE
NOTE:
Lower the
Voltage 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 “1.0 V” is recommended.
