GE 845 Instruction Manual page 437

CHAPTER 4: SETPOINTS
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Measured or calculated analog
value related to:
Frequency
Volt/Hz
RTDs
2
I t (arcing Amps)
Differential and Restraint currents
(Percent Differential)
Differential and Restraint currents
(RGF)
Winding Hottest-Spot
Loss of Transformer Life
Aging Factor
Harmomic Derating
Xfmr Overload
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 in figure: Direction,
Pickup, and Hysteresis setpoints.
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:
Base Unit
f = nominal frequency as entered under the SYSTEM
BASE
SETUP menu
BASE = 1.00
BASE = 1.00°C
2
BASE = 2000 kA *cycle
I = CT primary from the CT bank selected for Winding 1
BASE
(the same base as the one for 87T element)
I = CT primary from the CT bank selected for the RGF
BASE
element (the same base as the one for RGF element)
BASE = 1.00°C
LOL = 180000 hours
BASE
AAF = 1.00
BASE
HDF = 1.00
BASE
OL = 100%
BASE
FLEXLOGIC
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