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CHAPTER 4: SETPOINTS
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
HYSTERESIS
Range: 0.1 to 50.0% in steps of 0.1%
Default: 3.0%
This setting defines the pickup – drop out relation of the element by specifying the width
of the hysteresis loop as a percentage of the pickup value as shown above in the
Direction, Pickup, and Hysteresis setpoints figure.
RATE OF CHANGE TIME UNIT (dt)
Range: millisecond, second, minute
Default: milliseconds
This setting specifies the time base dt when programming the FlexElement as a rate of
change element.
The setting is applicable only if the Operating Mode is set to "Delta".
RATE OF CHANGE TIME
Range: 40 to 65535 in steps of 1
Default: 40
This setting specifies the duration of the time interval for the rate of change mode of
operation.
The setting is applicable only if the Operating Mode is set to "Delta".
EXAMPLES
13.8 kV power system:
•
Phase VT Connection: Wye
•
Phase VT Secondary: 66.4 V
•
Phase VT Ratio: 120:1 (phase to neutral primary voltage = 120*66.4 = 7968 V)
•
Aux VT Connection: Vab
•
Aux VT Secondary: 115 V
•
Aux VT Ratio: 120:1(phase-phase primary voltage = 13800V)
•
Phase CTs Primary: 2000 A
•
Ground CT Primary: 500 A
•
Frequency: 60Hz
Detecting voltage difference:
The voltage difference between calculated phase-phase voltage derived from Wye
connected phase VTs, and the directly measured phase-phase voltage from auxiliary VT
can be monitored by programming a FlexElement.
FlexElement settings:
•
Input 1(+): J2 Vab RMS
•
Input 2 (-): J2 Vaux RMS (input from VT connected between phases A and B)
•
Operating Mode: Absolute
•
Input Comparison Mode: Level
•
Direction: Over
The analog input J2 Vab is phase-phase voltage computed by the relay based on three-
phase Wye voltages. As per the Phase VT setup, the primary RMS nominal voltage for J2
Vab input is 66.4 V *120 = 7.968kV.
The analog input J2 Vaux is directly measured phase-phase voltage and its primary RMS
nominal voltage is 115V *120 = 13.8kV
V
= max (7.968kV, 13.8kV) = 13.8kV.
BASE
FLEXLOGIC
4–389
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