GE Multilin g60 Instruction Manual page 369

5 SETTINGS
d) SUB-HARMONIC STATOR GROUND FAULT

PATH: SETTINGS GROUPED ELEMENTS
 SH STATOR
 GROUND
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A voltage source placed at the neutral of the generator will produce a current for ground faults anywhere on the stator wind-
ing. This source is coupled to the primary circuit using the existing neutral grounding transformer. The following figure
shows a typical high impedance grounded generator that is protected against ground faults using the sub-harmonic injec-
tion method. The neutral resistor is chosen to limit the ground fault current to a low value (less than 25 A) in order to mini-
mize damage. A sub-harmonic frequency voltage signal is injected into the neutral of the generator. Under normal
conditions a resulting current flows through the surge capacitors (C
step-up transformer windings. When a ground fault develops on the stator winding, an additional current flows through the
resistance R . The value of R
G
An AC signal is injected so that it can be coupled through an injection transformer to the primary circuit. The signal is of a
low frequency in order to minimize the effects of the capacitance of the primary circuit. A frequency of 20 Hz is chosen.
Referring to the following figure, the admittance seen looking into the grounding transformer is:
In the above equation:
• R is the ground fault resistance.
G
• C is the total capacitance to ground.
T
• N is the neutral grounding transformer ratio.
GE Multilin

SETTING GROUP 1(6)
SH STATOR GROUND
FUNCTION: Disabled
SH STATOR GND STG1
PICKUP: 10 kΩ
SH STATOR GND STG1
DELAY: 10.0 s
SH STATOR GND STG2
PICKUP: 10 kΩ
SH STATOR GND STG2
DELAY: 10.0 s
SH CT ANGLE COMPEN:
0.00°
SH STATOR GND OC
PICKUP: 0.010 pu
SH STATOR GND OC
DELAY: 1.00 s
SH STATOR GND Vsupv:
0.000 pu
SH STATOR GND Isupv:
0.000 pu
SH STATOR GND BLK:
Off
SH STATOR GROUND
TARGET: Self-reset
SH STATOR GROUND
EVENTS: Disabled
is derived from the measurement of the injected voltage and the resulting current.
G
I
2
G
 ------ -
Y N
= =
V
X
G60 Generator Protection System
 
STATOR GROUND SH STATOR GROUND
Range: Disabled, Enabled
Range: 1 to 20 kΩ in steps of 1
Range: 0.1 to 600.0 s in steps of 0.1
Range: 1 to 20 kΩ in steps of 1
Range: 0.1 to 600.0 s in steps of 0.1
Range: –30.00 to 30.00° in steps of 0.01
Range: 0.001 to 1.000 pu in steps of 0.001
Range: 0.10 to 600.00 s in steps of 0.01
Range: 0.000 to 0.100 pu in steps of 0.001
Range: 0.000 to 0.100 pu in steps of 0.001
Range: FlexLogic™ operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
) and through the stray capacitance of the stator and
s
1
------- - jC
+
T
R
G
5.6 GROUPED ELEMENTS
(EQ 5.42)
5-209
5