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CHAPTER 5: SETPOINTS
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
5–43
5.7
S6 Voltage Elements
5.7.1
Undervoltage
PATH: SETPOINTS
ZV
S6 VOLTAGE ELEM.
Z
UNDERVOLTAGE
The undervoltage elements may be used for protection of the generator and/or its
auxiliary equipment during prolonged undervoltage conditions. They are active only when
the generator is online. The alarm element is definite time and the trip element can be
definite time or a curve. When the magnitude of the average phase-phase voltage is less
than the pickup
×
the generator rated phase-phase voltage, the element will begin to time
out. If the time expires, a trip or alarm will occur.
The curve reset rate is a linear reset time from the threshold of trip. If the VT type is
selected as None, VT fuse loss is detected, or the magnitude of
I
1
< 7.5% CT, the
undervoltage protection is disabled. The pickup levels are insensitive to frequency over the
range of 5 to 90 Hz.
The formula for the undervoltage curve is:
(EQ 5.18)
1
UNDERVOLTAGE
[
Z
]
UNDERVOLTAGE
ALARM: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN ALARM
RELAYS (2-5): ---5
Range: Any combination of Relays 2 to
5
MESSAGE
UNDERVOLTAGE ALARM
PICKUP: 0.85 x Rated
Range: 0.50 to 0.99
×
Rated in steps of
0.01
MESSAGE
UNDERVOLTAGE ALARM
DELAY: 3.0 s
Range: 0.2 to 120.0 s in steps of 0.1
MESSAGE
UNDERVOLTAGE ALARM
EVENTS: Off
Range: On, Off
MESSAGE
UNDERVOLTAGE
TRIP: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN TRIP
RELAYS (1-4): 1---
Range: Any combination of Relays 1 to
4
MESSAGE
UNDERVOLTAGE TRIP
PICKUP: 0.80 x Rated
Range: 0.50 to 0.99
×
Rated in steps of
0.01
MESSAGE
UNDERVOLTAGE TRIP
DELAY: 1.0 s
Range: 0.2 to 10.0 s in steps of 0.1
MESSAGE
UNDERVOLTAGE CURVE
RESET RATE: 1.4 s
Range: 0.0 to 999.9 s in steps of 0.1
MESSAGE
UNDERVOLTAGE CURVE
ELEMENT: Curve
Range: Curve, Definite Time
T
D
1
V V
pickup
⁄
–
----------------------------------
=
, when
V V
pickup
<