Basler Electric DGC-2020 - Manual (Page 177)

Overcurrent Protection (51-1, 51-2, 51-3)
Two sets of overcurrent 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
CT secondary side (DGC-2020). When a single-phase override contact input is received by the DGC-
2020, the overcurrent protection settings automatically switch from the three-phase settings to the single-
phase overcurrent protection settings.
When any of the phase currents increase above the pickup setting A for the duration of the overcurrent
time delay, an overcurrent condition is annunciated. An overcurrent annunciation can be user-selected to
trigger a pre-alarm
B (warning) or alarm B (shutdown). An overcurrent annunciation can also be user-
configured to close a programmable output.
The overcurrent time delay is controlled by a time dial setting C and a curve setting D . The curve setting can
be set at F (fixed), P (programmable), or one of 16 inverse time characteristic curves can be selected.
When the fixed curve setting is selected, the time dial setting determines the overcurrent time delay with
no regard to the generator current level. When one of the inverse time characteristic curves is selected,
the time dial setting, along with the level of measured generator current, determines the overcurrent time
delay. As overcurrent protection settings are entered in BESTCOMSPlus, a plot
E of the settings is
automatically created to illustrate the overcurrent pickup curve. The available time characteristic curves
are listed below and illustrated in Appendix A, Time Overcurrent Characteristic Curves.
•
A, standard inverse
•
L1, long inverse
•
B, very inverse
•
L2, long inverse
•
C, extremely inverse
•
M, moderately inverse
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D, definite
•
P, programmable
•
E1, extremely inverse
•
S1, short inverse
•
E2, extremely inverse
•
S2, short inverse
•
G, long inverse
•
V1, very inverse
•
I1, inverse
•
V2, very inverse
•
I2, inverse
A low-line scale factor setting F is used for automatic adjustment of the overcurrent 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 graph can be set G to display the 1 Phase or 3 Phase curve as determined by the settings on the left
side of the chart.
Selection of integrated reset or instantaneous reset characteristics H is also provided. Refer to Appendix A,
Time Overcurrent Characteristic Curves, when calculating time to reset.
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 current or in per unit I
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 Amps, and the rated data associated with them is
Rated Secondary Phase Amps (on the System Parameters, Rated Data screen).
•
Overcurrent 51-1 Three-Phase Pickup
•
Overcurrent 51-1 Single-Phase Pickup
•
Overcurrent 51-2 Three-Phase Pickup
•
Overcurrent 51-2 Single-Phase Pickup
•
Overcurrent 51-3 Three-Phase Pickup
•
Overcurrent 51-3 Single-Phase Pickup
The BESTCOMSPlus Overcurrent screen is illustrated in Figure 4-58. The 51-1 element is shown.
9400200990 Rev X DGC-2020 BESTCOMSPlus
® Software
4-67