GE 845 Instruction Manual page 318

PROTECTION
4–190
PICKUP
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 0.300 x CT
This setting defines the minimum Pickup level of the ground differential current required
for operation. The Pickup value is expressed in times Phase CT (primary) rating.
SLOPE
Range: 0 to 100% in steps of 1%
Default: 50%
This setting defines the slope as the ratio between the ground differential current and
the maximum line current (ground restraining current) as a percentage. The RGF 1
element operates if the actual ground differential/restraint ratio is greater than the slope
and the ground differential current is greater than the RGF 1 Pickup setting.
PICKUP DELAY
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 0.100 s
The RGF 1 Pickup Time Delay setting defines the time required for the RGF 1 element to
operate after it has picked up. This time delay overrides the spurious ground differential
current condition caused by CT saturation due to external non-ground faults, or during
transformer energization. Since RGF 1 protection is intended to detect small ground fault
currents, delayed clearance of such a fault is not a high concern. On the other hand
delayed RGF 1 operation due to a spurious ground differential current caused by an out-
of-zone fault can be used as a backup for downstream protections should they fail to
clear the fault.
GND CURR SUPERV
Range: Disabled, Enabled
Default: Disabled
This setting enables or disables the ground current supervision of the RGF 1 function. If
set to "Disabled", the RGF 1 function works without ground current supervision. The
ground current level is monitored if the setting is set to "Enabled".
GND CURR SUPERV LEVEL
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 0.300 x CT
This setting defines the level of measured ground current above which operation of the
RGF 1 protection is allowed. The setting is presented as a times ground CT (primary)
rating. The measured ground current is compared to the setting only if the GROUND
CURRENT SUPERVISION is set to "Enabled".
BLOCK
Range: Off, Any FlexLogic operand
Default: Off
OUTPUT RELAY X
For details see Common
EVENTS
Range: Enabled, Disabled
Default: Enabled
TARGETS
Range: Self-reset, Latched, Disabled
Default: Self-reset
Setpoints.
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS