GE G60 UR Series, Instruction Manual

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GE Multilin G60 Generator Protection System 5-165
5 SETTINGS 5.6 GROUPED ELEMENTS
5
d) RESTRICTED GROUND FAULT (ANSI 87G)
PATH: SETTINGS
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GROUPED ELEMENTS
Ö
SETTING GROUP 1(6)
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GROUND CURRENT
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RESTRICTED GROUND FAULT 1(4)
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 5–86: 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.
„
RESTRICTED GROUND
„
FAULT 1
RESTD GND FT1
FUNCTION: Disabled
Range: Disabled, Enabled
MESSAGE
RESTD GND FT1
SOURCE: SRC 1
Range: SRC 1, SRC 2, SRC 3, SRC 4
MESSAGE
RESTD GND FT1
PICKUP: 0.080 pu
Range: 0.005 to 30.000 pu in steps of 0.001
MESSAGE
RESTD GND FT1
SLOPE: 40%
Range: 0 to 100% in steps of 1
MESSAGE
RESTD GND FT1 PICKUP
DELAY: 0.10 s
Range: 0.00 to 600.00 s in steps of 0.01
MESSAGE
RESTD GND FT1 RESET
DELAY: 0.00 s
Range: 0.00 to 600.00 s in steps of 0.01
MESSAGE
RESTD GND FT1 BLOCK:
Off
Range: FlexLogic™ operand
MESSAGE
RESTD GND FT1
TARGET: Self-reset
Range: Self-reset, Latched, Disabled
MESSAGE
RESTD GND FT1
EVENTS: Disabled
Range: Disabled, Enabled
842731A1.CDR
35%
RGF
ZONE
DIFFERENTIAL ZONE
Rg
WINDING