4-36 DGC-2020 BESTCOMSPlus Software 9400200990 Rev I
Frequency Protection (81O/U)
Two sets of frequency protection settings are provided: one for underfrequency (81U) and one for
overfrequency (81O).
Underfrequency (81U)
An underfrequency condition is annunciated when the generator frequency decreases below the 81U
pickup setting
A
for the duration of the 81U activation delay setting
B
. An underfrequency annunciation can
be user-selected to trigger a pre-alarm
C
(warning) or alarm
C
(shutdown). An underfrequency annunciation
can also be user-configured to close a programmable output.
A voltage-based inhibit setting
D
prevents an 81U trip from occurring during an underfrequency condition
associated with system startup.
The hysteresis setting
E
functions as an underfrequency dropout by preventing rapid switching of the
pickup output.
Overfrequency (81O)
When the generator frequency increases above the 81O pickup setting
F
for the duration of the 81O
activation delay setting
G
, an overfrequency condition is annunciated. An overfrequency annunciation can
be user-selected to trigger a pre-alarm
H
(warning) or alarm
H
(shutdown). An overfrequency condition can
also be user configured to close a programmable output.
The hysteresis setting
I
functions as an overfrequency dropout by preventing rapid switching of the pickup
output.
BESTCOMSPlus frequency protection settings (DGC-2020, Generator Protection, Frequency) are
illustrated in
Figure 4-33.
Figure 4-33. Frequency Protection Settings
A
Underfrequency Pickup: Adjustable from 45 to 66 Hz in 0.1 Hz increments for 50/60 Hz controllers
(style number x1xxxxxxxx). Adjustable from 360 to 440 Hz in 0.1 Hz increments for 400 Hz controllers
(style number x2xxxxxxxx).
B
Underfrequency Activation Delay: Adjustable from 0 to 30 s in 0.1 s increments.
C
Underfrequency Alarm Configuration: None, Alarm, or Prealarm.
D
Underfrequency Inhibit Volts: Adjustable from 70 to 576 Vac in 1 Vac increments.
E
Hysteresis: Adjustable from 0.1 to 40 Hz in 0.1 Hz increments.
F
Overfrequency Pickup: Adjustable from 45 to 65 Hz in 0.1 Hz increments for 50/60 Hz controllers (style
number x1xxxxxxxx). Adjustable from 360 to 440 Hz in 0.1 Hz increments for 400 Hz controllers (style
number x2xxxxxxxx).
G
Overfrequency Activation Delay: Adjustable from 0 to 30 s in 0.1 s increments.
H
Overfrequency Alarm Configuration: None, Alarm, or Prealarm.
I
Hysteresis: Adjustable from 0.1 to 40 Hz in 0.1 Hz increments.
Reverse Power Protection (32)
Two sets of reverse power settings are provided: one for three-phase generator connections and one for
single-phase generator connections. The pickup setting entered is based on the CT secondary side
(DGC-2020). When a single-phase override contact input is received by the DGC-2020, the reverse
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