Neutral Undervoltage - GE Multilin 489 Instruction Manual

CHAPTER 5: SETPOINTS
5.7.8

Neutral Undervoltage

1 NEUTRAL U/V
(3rd HARMONIC)
Note
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
PATH: SETPOINTS S6 VOLTAGE ELEM.
[ ] LOW POWER BLOCKING
LEVEL: 0.05 x Rated
LOW VOLTAGE BLOCKING
MESSAGE
LEVEL: 0.75 x Rated
NEUTRAL UNDERVOLTAGE
MESSAGE
ALARM: Off
ASSIGN ALARM
MESSAGE
RELAYS (2-5): ---5
NEUTRAL U/V ALARM
MESSAGE
LEVEL: 0.5 Vsec
NEUTRAL UNDERVOLTAGE
MESSAGE
ALARM DELAY: 30 s
NEUTRAL UNDERVOLTAGE
MESSAGE
ALARM EVENTS: Off
NEUTRAL UNDERVOLTAGE
MESSAGE
TRIP: Off
ASSIGN TRIP
MESSAGE
RELAYS (1-4): 1---
NEUTRAL U/V TRIP
MESSAGE
LEVEL: 1.0 Vsec
NEUTRAL UNDERVOLTAGE
MESSAGE
TRIP DELAY: 30 s
The
LOW POWER BLOCKING LEVEL
setpoints are seen only if the
LEVEL
setpoint is "Delta"
The neutral undervoltage function responds to 3rd harmonic voltage measured at the
generator neutral and output terminals. When used in conjunction with the Neutral
Overvoltage (fundamental frequency) function, it provides 100% ground fault protection of
the stator windings.
For Wye connected VTs:
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. If the phase
VT connection is wye, the following formula is used to create an adaptive neutral
undervoltage pickup level based on the amount of third harmonic that appears at the
generator terminals.
V
N3
----------------------------------- - ≤
( V 3 ⁄ ) V
+
P3 N3
The 489 tests the following permissives prior to testing the basic operating equation to
ensure that V ' should be of a measurable magnitude for an unfaulted generator:
N3
NEUTRAL U/V (3RD HARMONIC)
Range: 0.02 to 0.99 × Rated MW in
Range: 0.50 to 1.00 × Rated in steps of
Range: Off, Latched, Unlatched
Range: Any combination of Relays 2 to
Range: 0.5 to 20.0 Vsec in steps of 0.1
Range: 5 to 120 s in steps of 1
Range: On, Off
Range: Off, Latched, Unlatched
Range: Any combination of Relays 1 to
Range: 0.5 to 20.0 Vsec in steps of 0.1
Range: 5 to 120 s in steps of 1
,
NEUTRAL U/V ALARM LEVEL
S2 SYSTEM SETUP VOLTAGE
0.15 which simplifies to V
P3
steps of 0.01
0.01
5
4
, and
NEUTRAL U/V TRIP
VT CONNECTION
≥ 17V
(EQ 5.24)
N3
5–53