GE Multilin 489 Instruction Manual page 164
Generator management relay
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Also See for Multilin 489:
- Instruction manual (306 pages) ,
- Communications manual (78 pages) ,
- Instruction manual (259 pages)
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Note
5–54
Courtesy of NationalSwitchgear.com
V
'
>
0.25 V and V
P3
where: V
= magnitude of the third harmonic voltage at generator neutral;
N3
V
= magnitude of the third harmonic voltage at the generator terminals
P3
V
´ = VT secondary magnitude of the third harmonic voltage measured at the
P3
generator terminals;
V
´ = VT sec. magnitude of 3
N3
Threshold = 0.15 V for the alarm element and 0.1875 V for the trip element
For Open Delta connected VTs:
If the phase VT connection is open delta, it is not possible to measure the third harmonic
voltages at the generator terminals and a simple third harmonic neutral undervoltage
element is used. The level is programmable in terms of Neutral VT secondary voltage. In
order to prevent nuisance tripping at low load or low generator voltages, two blocking
functions are provided. They apply to both the alarm and trip functions. When used as a
simple undervoltage element, settings should be based on measured 3rd harmonic
neutral voltage of the healthy machine.
This method of using 3rd harmonic voltages to detect stator ground faults near the
generator neutral has proved feasible on generators with unit transformers. Its usefulness
in other generator applications is unknown.
Neutral VT Ratio
'
≥
Threshold 17
×
×
--------------------------------------- -
P3
Phase VT Ratio
rd
harmonic voltage at generator neutral;
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
(EQ 5.25)
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