Basler Electric DGC-2020HD - Manual (Page 158)

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Pickup and Trip
When a generator’s excitation power is lost, the generator acts as a large inductor as it begins to absorb
large quantities of vars. The 40Q element acts on the principal that if a generator begins to absorb vars
outside of its steady-state capability curve, it has likely lost its normal excitation supply. It compares the
reactive power to the 40Q response curve defined by the Pickup setting. When the reactive power is
within the 40Q tripping region, a timer begins timing towards a trip. Refer to Figure 84.
Timer duration is established by the Activation Delay. Activation delays are recommended for tripping.
Adding a small delay will help assure that false alarms do not occur for transient fault conditions or swings
in the power system. An Activation Delay of zero (0) makes the 40Q element with no intentional time
delay.
If a loss of excitation 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 loss of excitation.
Figure 84. Generator Capability Curve vs. 40Q Response
Hysteresis
The hysteresis setting functions as a loss of excitation dropout by preventing rapid switching of the pickup
output.
Low-Line Scale Factor
A low-line scale factor setting is used to automatically adjust the loss of excitation pickup setting in
applications that might utilize more than one type of genset connection. The scale factor setting is
implemented when the DGC-2020HD is determined to be in a low-line configuration. If the Low-Line
Override function is assigned to a contact input via the Programmable Functions screen, the state of the
contact input and the detected configuration are ORed. This means, if one or both are true, then the
system is determined to be configured for low-line. The value of the scale factor setting serves as a
multiplier for the pickup setting. For example, if a scale factor contact input is received by the DGC-
2020HD and the scale factor setting is 2.000, the pickup setting will be doubled (2.000 x PU).
Alarm Configuration
A loss of excitation annunciation can be user-selected to trigger a pre-alarm (warning) or alarm
(shutdown). A loss of excitation annunciation can also be user-configured to close a programmable
output.
Element status is available in BESTlogicPlus programmable logic when “Status Only” is selected.
Generator Protection DGC-2020HD