Negative Sequence Overvoltage Protection - GE 845 Instruction Manual

CHAPTER 4: SETPOINTS
Negative Sequence
Overvoltage
Protection
FASTPATH:
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
The 845 relay provides one Negative Sequence Overvoltage (Negative Sequence OV 1)
element per protection group, or a total of 6 elements.
The Negative Sequence Overvoltage element can be used to detect an asymmetrical
system voltage condition, loss of one or two phases of the source, or reversed phase
sequence of voltages. The element responds to the negative sequence voltage (V_2),
calculated from the phase voltages. The Negative Sequence Overvoltage element may be
set as an instantaneous element with no time delay, or may be set as a definite time
element.
The settings of this function are applied to the calculated Negative Sequence Voltage to
produce Pickup and Trip flags. The Negative Sequence OV Pickup flag is asserted when the
Negative Sequence Voltage is above the PKP value. The Negative Sequence OV Trip flag is
asserted if the element stays picked up for the time defined by Pickup time delay. The
element drops from Pickup without operation if the calculated Negative Sequence Voltage
drops below 97 to 98% of the Pickup value before the time for operation is reached.
Path:
Setpoints > Protection > Group 1(6) > Voltage > Neg Seq OV 1
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
PICKUP
Range: 0.00 to 3.00 x VT in steps of 0.01 x VT
Default: 1.00 x VT
This setting sets the Negative Sequence Overvoltage Pickup level specified per times VT.
For example, a Pickup setting of 0.80 x VT with 13800:115 VT translates into 11.04 kV (or
92 V secondary).
If the 3 phase VT is delta connected, the Negative Sequence Overvoltage pickup level is
internally changed to 1/sqrt(3) of the user setting, before being compared to the actual
negative sequence voltage.
PICKUP DELAY
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 1.000 s
DROPOUT DELAY
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 1.000 s
BLOCK
Range: Off, Any operand from the list of FlexLogic operands
Default: Off
PROTECTION
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