GE Multilin g60

GE Multilin G60 Generator Protection System 5-209
5 SETTINGS 5.6 GROUPED ELEMENTS
5
d) SUB-HARMONIC STATOR GROUND FAULT
PATH: SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1(6)  STATOR GROUND  SH STATOR GROUND
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
s
) and through the stray capacitance of the stator and
step-up transformer windings. When a ground fault develops on the stator winding, an additional current flows through the
resistance R
G
. The value of R
G
is derived from the measurement of the injected voltage and the resulting current.
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:
(EQ 5.42)
In the above equation:
• R
G
is the ground fault resistance.
• C
T
is the total capacitance to ground.
• N is the neutral grounding transformer ratio.
 SH STATOR
 GROUND
SH STATOR GROUND
FUNCTION: Disabled
Range: Disabled, Enabled
MESSAGE
SH STATOR GND STG1
PICKUP: 10 k
Range: 1 to 20 k in steps of 1
MESSAGE
SH STATOR GND STG1
DELAY: 10.0 s
Range: 0.1 to 600.0 s in steps of 0.1
MESSAGE
SH STATOR GND STG2
PICKUP: 10 k
Range: 1 to 20 k in steps of 1
MESSAGE
SH STATOR GND STG2
DELAY: 10.0 s
Range: 0.1 to 600.0 s in steps of 0.1
MESSAGE
SH CT ANGLE COMPEN:
0.00°
Range: –30.00 to 30.00° in steps of 0.01
MESSAGE
SH STATOR GND OC
PICKUP: 0.010 pu
Range: 0.001 to 1.000 pu in steps of 0.001
MESSAGE
SH STATOR GND OC
DELAY: 1.00 s
Range: 0.10 to 600.00 s in steps of 0.01
MESSAGE
SH STATOR GND Vsupv:
0.000 pu
Range: 0.000 to 0.100 pu in steps of 0.001
MESSAGE
SH STATOR GND Isupv:
0.000 pu
Range: 0.000 to 0.100 pu in steps of 0.001
MESSAGE
SH STATOR GND BLK:
Off
Range: FlexLogic™ operand
MESSAGE
SH STATOR GROUND
TARGET: Self-reset
Range: Self-reset, Latched, Disabled
MESSAGE
SH STATOR GROUND
EVENTS: Disabled
Range: Disabled, Enabled
YN
2
I
G
V
X
-------

1
R
G
------- - jC
T
+==