GE T60 Instruction Manual page 368

5.6 GROUPED ELEMENTS
d) RESTRICTED GROUND FAULT (ANSI 87RGF, IEC PNDF)

PATH: SETTINGS GROUPED ELEMENTS
 RESTRICTED GROUND
 FAULT 1
5
As of T60 firmware revision 3.20, the definition of the restraining signal has been significantly changed
compared to previous versions. The restraint during external faults is generally not lower, and often much
higher, compared to the previous definition of the restraining signal (enhanced security). The restraint on
NOTE
internal faults has been greatly reduced compared to previous versions (enhanced sensitivity), particularly
during low-current internal faults. Using time delay as a means of dealing with CT saturation is no longer
obligatory; pickup and slope are the primary means of addressing CT saturation. Increasing the slope set-
ting is recommended when migrating from the 3.1x or earlier firmware revisions. The default value for the
slope has been changed from 10% to 40%.
Restricted ground fault (RGF) protection provides sensitive ground fault detection for low-magnitude fault currents, primar-
ily faults close to the neutral point of a wye-connected winding. An internal ground fault on an impedance grounded wye
winding will produce a fault current dependent on the ground impedance value and the fault position on the winding with
respect to the neutral point. The resultant primary current will be negligible for faults on the lower 30% of the winding since
the fault voltage is not the system voltage, but rather the result of the transformation ratio between the primary windings
and the percentage of shorted turns on the secondary. Therefore, the resultant differential currents may be below the slope
threshold of the main differential element and the fault could go undetected. Application of the restricted ground fault pro-
tection extends the coverage towards the neutral point (see the RGF and Percent Differential Zones of Protection diagram).
Figure 5–116: RGF AND PERCENT DIFFERENTIAL ZONES OF PROTECTION
5-232

SETTING GROUP 1(6)
RESTD GND FT1
FUNCTION: Disabled
RESTD GND FT1
MESSAGE
SOURCE: SRC 1
RESTD GND FT1
MESSAGE
PICKUP:
RESTD GND FT1
MESSAGE
SLOPE: 40%
RESTD GND FT1 PICKUP
MESSAGE
DELAY: 0.10 s
RESTD GND FT1 RESET
MESSAGE
DELAY: 0.00 s
RESTD GND FT1 BLOCK:
MESSAGE
Off
RESTD GND FT1
MESSAGE
TARGET: Self-reset
RESTD GND FT1
MESSAGE
EVENTS: Disabled
35%
RGF
Rg
ZONE
T60 Transformer Protection System

GROUND CURRENT
Range: Disabled, Enabled
Range: SRC 1, SRC 2, SRC 3, SRC 4, SRC 5, SRC 6
Range: 0.005 to 30.000 pu in steps of 0.001
0.080 pu
Range: 0 to 100% in steps of 1
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.00 to 600.00 s in steps of 0.01
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
WINDING
DIFFERENTIAL ZONE
842731A1.CDR
5 SETTINGS

RESTRICTED GROUND FAULT 1(6)
GE Multilin