GE G30 Instruction Manual page 288

5.6 GROUPED ELEMENTS
d) RESTRICTED GROUND FAULT (ANSI 87RGF, IEC PNDF)

PATH: SETTINGS GROUPED ELEMENTS
 RESTRICTED GROUND
 FAULT 1
5
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 5–66: RGF AND PERCENT DIFFERENTIAL ZONES OF PROTECTION
This protection is often applied to transformers having impedance-grounded wye windings. The element may also be
applied to the stator winding of a generator having the neutral point grounded with a CT installed in the grounding path, or
the ground current obtained by external summation of the neutral-side stator CTs. The Typical Applications of RGF Protec-
tion diagram explains the basic application and wiring rules.
5-158

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
G30 Generator Protection System

GROUND CURRENT
Range: Disabled, Enabled
Range: SRC 1, SRC 2, SRC 3, SRC 4
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(4)
GE Multilin