Basler Electric DGC-2020HD - Manual (Page 137)

9469300990 Rev B 127
Generator Protection
Two tiers of generator protection are offered. DGC-2020HD controllers with style number xxSxxxxxx offer
standard protection consisting of undervoltage (27), overvoltage (59), overfrequency (81O),
underfrequency (81U), power (32), and loss of excitation (40Q) elements. Controllers with style number
xxExxxxxx offer enhanced protection, which consists of the standard protection elements plus phase
voltage imbalance (47), time overcurrent (51), vector shift (78), and frequency rate-of-change (ROC)
elements.
Four setting groups enable independent protection coordination which is selectable in BESTlogicPlus.
Setting groups are described at the end of this chapter.
Undervoltage (27)
Six undervoltage protection (27) elements monitor the sensing voltage applied to the DGC-2020HD. An
element can be configured to protect against undervoltage when the phase voltage decreases below a
defined level.
The six, identical undervoltage protection elements are designated 27-1, 27-2, 27-3, 27-4, 27-5, and 27-6.
Element logic connections are made on the BESTlogic
™Plus screen in BESTCOMSPlus® and element
operational settings are configured on the Undervoltage settings screen in BESTCOMSPlus.
BESTCOMSPlus Navigation Path: Settings Explorer, Generator Protection, Voltage, Undervoltage (27)
Front Panel Navigation Path: Settings Explorer > Protection > Settings Group x (where x = 0 to 3) >
Voltage Protection > Undervoltage (27P)
Element Operation
Undervoltage protection can be used to prevent equipment damage when an undervoltage condition
exists.
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
PT secondary side (DGC-2020HD). When a single-phase override contact input is received, the DGC-
2020HD automatically switches from the three-phase undervoltage settings to the single-phase
undervoltage settings.
Source
The Source setting configures an undervoltage element to monitor the generator sensing input terminals
or the bus sensing input terminals.
Pickup and Trip
When the average of the three-phase voltage (three-phase mode) or the line-to-line voltage (single-phase
mode) decreases below the threshold established by the Pickup setting, a timer begins timing towards a
trip.
The duration of the timer is established by the Activation Delay. An Activation Delay of zero (0) makes the
27 element instantaneous with no intentional time delay.
If an undervoltage pickup condition persists for the duration of the element Activation Delay setting, the
element Trip output becomes true. In BESTlogicPlus, the Trip output can be connected to other logic
elements or a physical relay output to annunciate the condition and initiate corrective action.
If the pickup condition subsides before the element activation delay expires, the timer is reset, no
corrective action is taken, and the element is rearmed for any other occurrences of undervoltage.
Hysteresis
The hysteresis setting functions as an undervoltage dropout by preventing rapid switching of the pickup
output.
DGC-2020HD Generator Protection