GE Multilin 489 Instruction Manual page 277

CHAPTER A: APPENDIX
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
grounding impedance is inductive, the plane of operation will be the 270° plane, again,
with the polarity convention shown below. If the polarity convention is reversed on one
input, the user will need to change the plane of operation by 180°.
GENERATOR
CORE
BALANCE
I
o
I
o
±
F10 H10
489
I
o
Relay
G10
E10
±
Isolating
Transformer
FIGURE A–4: Ground Directional Element Polarities and Plane of Operation
Aux.
Contact
Grounding
Switch
To Relay
Grounding
Impedance V
neutral
(Trans. & Input
Resistor)
Isolating
Transformer
Grounding
Switch
Aux. Cont.
FIGURE A–5: Ground Directional Element Conceptual Arrangement
The operating principle of this element is quite simple: for internal ground faults the two
signals will be 180° out of phase and for external ground faults, the two signals will be in
phase. This simple principle allows the element to be set with a high sensitivity, not
normally possible with an overcurrent element.
The current pickup level of the element can be adjusted down to 0.05 × CT primary,
allowing an operate level of 0.25 A primary if the 50:0.025 ground CT is used for the core
balance. The minimum level of V
hardware limitations and is internally set at 2.0 V.
Because this element is directional, it does not need to be coordinated with downstream
protections and a short operating time can be used. Definite time delays are suitable for
this element.
CT
Plane of operation
for resistive
grounding impedance
180°
V
o
GENERATOR
489
Ground
Directional
Element
(or O/C)
Ground
Neutral
O/C
O/V
Element
Element
G.S.
Breaker
Status Status
at which the element will operate is determined by
neutral
90°
I
o
0°
270°
808735A1.CDR
CORE
BREAKER
BALANCE
CT
Aux.
Breaker
Ground
Current
Input
808734A1.CDR
A–5