GE 845, Instruction Manual

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4–200 845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION CHAPTER 4: SETPOINTS
Phase Undervoltage
Protection (27P)
The 845 relay is equipped with the Phase Undervoltage (UV) element. The Phase
Undervoltage element may be used to protect voltage sensitive loads and system
components against sustained undervoltage conditions. This element may be used for
permissive functions, initiation of the source transfer schemes, and similar functions.
The Phase Undervoltage element may be set as an instantaneous element with no time
delay or as a time delayed element which can be programmed with definite time, inverse
time or FlexCurves. The Phase Undervoltage element has programmable minimum
operating threshold to prevent some undesired operation when voltage is not available.
The input voltages are the three phase to phase voltages from delta connected VTs (PTs) or
three phase to ground voltages from wye connected VTs (PTs).
The settings of this function are applied to each of the three voltage inputs to produce
Pickup and Trip flags per voltage input. The UV Pickup flag is asserted, when the measured
voltage on any of the three voltage inputs is below the PKP value. The UV Trip flag is
asserted if the element stays picked up for the time defined by Pickup time delay or for the
time defined by the selected inverse curve / FlexCurve, and number of voltages required
for operation matches the number of voltages selected in the setting. The element drops
from Pickup without operation if the measured voltage rise above 102 to 103% of the
Pickup value, before the time for operation is reached.
The minimum voltage setting selects the operating voltage below which the element is
blocked (a setting of “0” allows a dead source to be considered a fault condition).
This element may be used to give a desired time delay operating characteristic versus the
applied voltage (phase to ground or phase to phase for wye VT connection, or phase to
phase for delta VT connection) or as a definite time element. For the inverse time setpoint,
the undervoltage delay setpoint defines a family of curves as described in
Undervoltage
Curves .
Path :
Setpoints > Protection > Group 1(6) > Voltage Elements > Phase UV 1(X)
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
MODE
Range: Phase to Ground, Phase to Phase
Default: Phase to Ground
This setting provides the selection of phase to ground and phase to phase voltages for a
Wye VT connection (phase to phase for delta connected VT connection).
FASTPATH:
Only Phase to Phase mode shall be selected when Delta is programmed for the Phase VT
Connection setting under System/Voltage Sensing.
PICKUP
Range: 0.00 to 1.50 x VT in steps of 0.01 x VT
Default: 1.00 x VT
This setting sets the Phase Undervoltage Pickup level specified per times VT.
For example, a Pickup setting of 0.80 x VT with a 13800:115 VT translates into 11.04kV (or
92V secondary). If the mode selection is phase to phase and the Setpoints/System
Setup/Voltage Sensing/Phase VT Connection selection is Wye, the previous example
translates to the phase to phase voltage value of 11.04kV x 1.732 = 19.12kV.