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CHAPTER 4: SETPOINTS
Wattmetric Ground
Fault
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
The Wattmetric Ground Fault element, also called Wattmetric Zero-sequence Directional
element, responds to power derived from zero-sequence voltage and current in a direction
specified by the element characteristic angle. The angle can be set within all four
quadrants and the power can be active or reactive. Therefore, the element may be used to
sense either forward or reverse ground faults in inductive, capacitive or resistive networks.
The inverse time characteristic allows time coordination of elements across the network.
Typical applications include Ground Fault protection in grounded/ungrounded/resistor-
grounded/resonant-grounded distribution networks, or directionalizing other non-
directional ground elements.
Path:
Setpoints > Protection > Group 1(6) > Power > Wattmetric Ground Fault
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
VOLTAGE
Range: Calculated VN, Measured Vx
Default: Calculated VN
The element uses neutral voltage (that is, three times the zero-sequence voltage). The
setting allows selecting the internally calculated neutral voltage, or externally supplied
voltage (broken delta VT connected to the auxiliary channel bank of the relay). When the
latter selection is made, the auxiliary channel must be identified by the user as a neutral
voltage under the VT bank settings. This element operates only if the auxiliary voltage is
configured as neutral.
VOLTAGE PICKUP
Range: 0.02 to 3.00 x VT in steps of 0.01 x VT
Default: 0.20 x VT
The setting specifies the minimum zero sequence voltage supervising the directional
power measurement. This threshold is higher than possible unbalance during normal
operation of the system. Typically, this setting is selected at 0.1 to 0.2 x VT for the
ungrounded or resonant grounded systems, and at 0.05 to 0.1 x VT for solidly or resistor-
grounded systems. When using externally supplied voltage via the auxiliary voltage
channel, 1 x VT is the nominal voltage of this channel as per VT bank settings. When
using internally calculated neutral voltage, 1 x VT is the nominal phase-to-ground
voltage per the VT bank settings.
PROTECTION
4–217
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