GE D90 Plus Instruction Manual page 150

POWER SYSTEM
NOTE:
Calculating the power cut-off level
142
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
Plus
D90 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.
Lower the
Voltage Cutoff Level
valid measurements. Unless dictated otherwise by a specific application, the default
setting of "1.0 V" is recommended.
The Current Cutoff Level and the
metered power cut-off levels. The power cut-off level is calculated as shown below. For
delta connections, the power cut-off is calculated as follows.
where VT primary = VT secondary × VT ratio and CT primary = CT secondary × CT ratio.
For wye connections, the three-phase and per-phase power cut-off values are calculated
as follows.
where VT primary = VT secondary × VT ratio and CT primary = CT secondary × CT ratio.
For example, given the following settings:
setting with care as the D90
Voltage Cutoff Level settings are used to determine the
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION
Plus
accepts lower signals as
Eq. 4
Eq. 5
Eq. 6