GE G60 Instruction Manual page 401

5 SETTINGS
• In addition the relay should be set properly with frequency tracking enabled and the source used as
should be the one connected to generator terminal VTs. The tracking frequency, which is essen-
PHASE REFERENCE
tially the generator frequency, will be used to block the sub-harmonic stator ground protection and auxiliary over volt-
age protection in the frequency range of 15 to 25 Hz.
b) 100% STATOR GROUND

PATH: SETTINGS GROUPED ELEMENTS
 100% STATOR
 GROUND
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
The 100% stator ground function responds to third harmonic voltage measured at the generator neutral and output termi-
nals. When used in conjunction with the neutral overvoltage (fundamental frequency) element, it provides 100% ground
fault protection of the stator windings. Since the amount of third harmonic voltage that appears in the neutral is both load
and machine dependent, the protection method of choice is an adaptive method. The following formula is used to create an
adaptive operating quantity based on the amount of third harmonic that appears at the generator terminals.
V
N 3rd ( )
---------------------------------------------
< Pickup
V V
+
( ) ( )
N 3rd 0 3rd
where: V is a magnitude of the 3rd harmonic in the voltage measured at the machine neutral point measured via an
N(3rd)
auxiliary channel of the VT bank, and
V is a magnitude of the 3rd harmonic in the zero-sequence voltage measured at the machine terminals.
0(3rd)
This element requires wye-connected VTs for measurement of the third harmonic in the zero-sequence
voltage at the generator output terminals.
NOTE
Example 1: Operating quantities under normal conditions.
Consider the figure shown below. In the case of a high impedance grounded machine, the neutral resistor is typically cho-
sen such that power dissipated in the resistor during a single line to ground fault is approximately equal to the reactive
power produced by the zero sequence capacitance of the stator winding and the GSU LV winding (
frequencies, the neutral resistance is therefore equal to
For analysis, assume that E
3
GE Multilin

SETTING GROUP 1(6)
100% STATOR GROUND
FUNCTION: Disabled
100% STATOR GND STG1
PICKUP: 0.150 pu
100% STATOR GND STG1
DELAY: 1.00 s
100% STATOR GND STG1
SUPV: 0.0057 pu
100% STATOR GND STG2
PICKUP: 0.150 pu
100% STATOR GND STG2
DELAY: 0.00 s
100% STATOR GND STG2
SUPV: 0.0045 pu
100% STATOR GND BLK:
Off
100% STATOR GROUND
TARGET: Self-reset
100% STATOR GROUND
EVENTS: Disabled
V
0 3rd ( )
---------------------------------------------
and >
V V
+
( ) ( )
N 3rd 0 3rd
X
oc
10 V , R 5Ω, and X 5Ω
= = =
c
G60 Generator Protection System
 
STATOR GROUND 100% STATOR GROUND
Range: Disabled, Enabled
Range: 0.000 to 0.900 pu in steps of 0.001
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.0010 to 0.1000 pu in steps of 0.0001
Range: 0.000 to 0.900 pu in steps of 0.001
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.0010 to 0.1000 pu in steps of 0.0001
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
1 Pickup and V
– +
( )
N 3rd
3 ⁄ ×
, and at 3 F , the neutral resistance is
n
.
5.6 GROUPED ELEMENTS
FREQUENCY AND
V > Supervision
(EQ 5.35)
( )
0 3rd
X ). At power system
oc
X .
oc
5-241
5