Basler Electric DGC-2020 - Manual (Page 170)

Undervoltage (27-1, 27-2)
Two sets of undervoltage settings are provided for each element: one for three-phase generator
connections and one for single-phase generator connections. The pickup setting entered is based on the
VT secondary side (DGC-2020). When a single-phase override contact input is received, the DGC-2020
automatically switches from the three-phase undervoltage settings to the single-phase undervoltage
settings.
An undervoltage condition is annunciated when the average of the three-phase (three-phase mode) or
the line-to-line voltage (single-phase mode) decreases below the corresponding 27 pickup setting
A for the
duration of the corresponding 27 activation delay B . An undervoltage annunciation can be user-selected to
trigger a pre-alarm C (warning) or alarm C (shutdown). An undervoltage annunciation can also be user-
configured to close a programmable output.
The hysteresis setting D functions as an undervoltage dropout by preventing rapid switching of the pickup
output.
A frequency-based inhibit setting E prevents a 27 trip from occurring during an undervoltage condition
associated with system startup.
A low-line scale factor setting F is used to automatically adjust the undervoltage pickup settings in
applications that might utilize more than one type of genset connection. The scale factor setting is
implemented when the DGC-2020 senses a contact closure at a contact input programmed to activate
scaling of the protection settings. The value of the scale factor setting serves as a multiplier for the pickup
settings. For example, if a scale factor contact input is received by the DGC-2020 and the scale factor
setting is 2.000, the pickup setting will be doubled (2.000
× PU).
The element is disabled when Alarm Configuration is set to “None”. Element status is available in
BESTlogicPlus Programmable Logic when “Status Only” is selected.
Settings which are related to machine ratings can be set in either actual units of voltage or in per unit G
values. When a native unit is edited, BESTCOMSPlus automatically recalculates the per unit value based
on the native unit setting and the rated data parameter (on the System Parameters, Rated Data screen)
associated with it. When a per unit value is edited, BESTCOMSPlus automatically recalculates the native
value based on the per unit setting and the rated data parameter associated with it.
Once all per unit values are assigned, if the rated data parameters are changed, BESTCOMSPlus
automatically recalculates all native unit settings based on the modified rated data parameters.
The following settings have native units of Secondary Volts, and the rated data associated with them is
Rated Secondary Volts (on the System Parameters, Rated Data screen).
•
Undervoltage 27-1 Three-Phase Pickup
•
Undervoltage 27-1 Single-Phase Pickup
•
Undervoltage 27-2 Three-Phase Pickup
•
Undervoltage 27-2 Single-Phase Pickup
The BESTCOMSPlus Undervoltage screen is illustrated in Figure 4-51. The 27-1 element is shown.
Figure 4-51. Undervoltage
4-60 DGC-2020 BESTCOMSPlus
® Software
9400200990 Rev X