GE G60 Instruction Manual page 250

5.5 GROUPED ELEMENTS
b) 100% STATOR GROUND
PATH: SETTINGS GROUPED ELEMENTS
100% STATOR
GROUND
5
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
--------------------------------------------- <
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
5-152
SETTING GROUP 1(6)
100% STATOR GROUND
FUNCTION: Disabled
100% STATOR GND STG1
MESSAGE
PICKUP: 0.150 pu
100% STATOR GND STG1
MESSAGE
DELAY: 1.00 s
100% STATOR GND STG1
MESSAGE
SUPV: 0.0075 pu
100% STATOR GND STG2
MESSAGE
PICKUP: 0.150 pu
100% STATOR GND STG2
MESSAGE
DELAY: 1.00 s
100% STATOR GND STG2
MESSAGE
SUPV: 0.0075 pu
100% STATOR GND BLK:
MESSAGE
Off
100% STATOR GROUND
MESSAGE
TARGET: Self-reset
100% STATOR GROUND
MESSAGE
EVENTS: Disabled
V
( )
0 3rd
---------------------------------------------
Pickup and
V V
+
N 3rd ( ) 0 3rd
E 10 V , R 5Ω, and X
= =
3
G60 Generator Management Relay
STATOR GROUND
Range: Disabled, Enabled
Range: 0.000 to 0.250 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 0.250 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
( )
X 3 ⁄ , and at 3 F × , the neutral resistance is
oc n
5Ω .
=
c
5 SETTINGS
100% STATOR GROUND
>
V Supervision
+
( ) 0 3rd ( )
X ). At power system
oc
X .
oc
(EQ 5.35)
GE Multilin