Thermal Inputs - GE 845 Instruction Manual

CHAPTER 4: SETPOINTS

Thermal Inputs

NOTE:
NOTE:
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
MINIMUM CURRENT
Range: 0.020 to 0.500 x CT in steps of 0.001
Default: 0.050 x CT
Select the minimum current, below which the transformer is considered de-energized.
Note that, if no load is connected to a transformer which has been energized, the
current transformers from the closed breaker will detect only the transformer
magnetizing current. In order to have Transformer energized status supervised by
current, the level of the minimum current must be below the transformer magnetizing
current.
The 845 relay can be set to monitor the hottest-spot winding temperature, the aging
acceleration factor and the transformer insulation life. In order for the relay to perform the
correct calculations, the user needs to enter transformer data and program RTD inputs for
measuring ambient and top-oil temperatures. The following menu shows the selections for
ambient and top-oil temperatures.
Path:
Setpoints > System > Transformer > Thermal Inputs
WINDING CURRENTS
Range: CT Bank1-J1, CT Bank 2 – K1, CT Bank 3 –K2
Default: CT Bank 1-J1
Select the bank representing the currents (loading) of the winding to which the thermal
elements are applied.
AMBIENT TEMPERATURE
Range: Monthly Average, RTD 1, RTD 2....RTD x
Default: Monthly Average
Select RTD input if the ambient temperature is to be measured directly. Select the
"Monthly Average" setting and enter an average temperature for every month of the
year, if direct ambient temperature measurement is not available.
The setpoints for average monthly temperatures will show on the screen only when the
"Monthly Average" setting is selected. In all other cases, these setpoints will be hidden.
AMBIENT TEMPERATURE AVG - Jan to Dec
Range: -60°C to 60°C (-76°F to 140°F) in steps of 1°C
Default: Jan= -20, Feb= -20, Mar= -10, Apr= 10, May= 20, Jun= 30, Jul= 30, Aug= 30, Sep=
20, Oct= 10, Nov= 10, Dec= -10
TOP-OIL TEMPERATURE
Range: Computed, RTD 1, RTD 2....RTD x
Default: Computed
Select RTD input for direct measurement of top-oil temperature. If such input is not
available, select the setting "Computed".
Refer to SETPOINTS/RTD Temperature, on how to select RTD, to be used for measuring
ambient and top-oil temperatures.
SYSTEM
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