GE 845 - Page 346

4–218 845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION CHAPTER 4: SETPOINTS
VOLTAGE MODE
Range: Phase-ground, Phase-phase
Default: Phase-ground
If the Phase VT Connection is selected as “Wye”, then the Voltage Mode setting further
defines the operating quantity and per-unit value for this element. If the Voltage Mode is
set as “Phase-phase”, then the operating quantity for this element will be phase-to-
phase nominal voltage. Likewise, if the Voltage Mode is set to “Phase-ground”, then the
operating quantity for this element will be the phase-to-ground nominal voltage.
If the Phase VT Connection (set under
Setpoint > System > Voltage Sensing) is selected as
“Delta”, then the phase-to-phase nominal voltage is used to define the per-unit value,
regardless of the Voltage Mode selection.
PICKUP
Range: 0.80 to 4.00 V/Hz in steps of 0.01
Default: 1.05 V/Hz
Enter the Volts per Hertz value (in V/Hz) above which the Volts per Hertz 1 element will
pickup.
CURVE
Range: Definite Time, Inverse A, Inverse B, Inverse C, FlexCurve A, FlexCurve B,
FlexCurve C, FlexCurve D
Default: Definite Time
Definite Time:
For the definite time curve, T(s) = TD multiplier. For example, setting the TD multiplier to
20 results in a time delay of 20 seconds to operate when above the Volts/Hz pickup
setting. Instantaneous operation can be obtained the same way by setting the TD
multiplier to “0”.
Inverse Curve A:
The curve for the Volts/Hertz Inverse Curve A shape is derived from the formula:
where: T = Operating Time
TDM= Time Delay Multiplier (delay in seconds)
V = fundamental RMS value of voltage (pu)
F = frequency of voltage signal (pu)
Pickup = volts-per-hertz pickup setpoint (pu)
The volts/hertz inverse A curves are shown below.
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