GE 489 Instruction Manual page 281

APPENDIX B
Grounding
Resistor
Figure B–5: GROUND DIRECTIONAL ELEMENT POLARITIES AND PLANE OF OPERATION
Applications with generators operated in parallel and grounded through a common impedance require special consider-
ations. If only one generator is grounded and the other ones left floating, the directional element for the floating generators
does not receive a correct V
neutral
use of auxiliary contacts off the grounding switch and the unit breaker to turn the element into a simple overcurrent element,
with the pickup level set for the directional element (note that the ground directional element and the ground overcurrent
elements are totally separate elements). In this mode, the element can retain a high sensitivity and fast operate time since
it will only respond to internal stator ground faults. The table below illustrates the status of different elements under various
operating conditions.
Table B–1: DETECTION ELEMENT STATUS
GENERATOR UNIT
CONDITION BREAKER
Shutdown Open
Open Circuit and Open
grounded
Loaded and Closed
Grounded
Loaded and Not Closed
Grounded
GE Power Management
GENERATOR
I
o
I
o
±
F10 H10
489
I
Relay
G10
E10
±
Isolating
Transformer
signal and therefore cannot operate correctly. In those applications, the element makes
GROUNDING
SWITCH
GROUND
DIRECTIONAL
Open Out-of-service
Closed In-service (but will not
operate due to lack of LO)
Closed
Open In service as a simple
overcurrent element
489 Generator Management Relay
B.1 STATOR GROUND FAULT PROTECTION
CORE
BALANCE
CT
Plane of operation
for resistive
grounding impedance
180°
V
o
o
ELEMENT
NEUTRAL
OVERVOLTAGE
Out-of-service
In-service
In-service In-service
Out-of-service
90°
I
o
0°
270°
GDECON2R2.CDR
GROUND
OVERCURRENT
In-service
In-service
In-service
In-service
B-5
B