Basler Electric DGC-2020HD - Manual (Page 145)

9469300990 Rev B 135
Figure 74. Settings Explorer, Generator Protection, Loss of Mains Protection, Vector Shift
Frequency (81)
Eight frequency protection (81) elements monitor the frequency of the sensing voltage applied to the
DGC-2020HD. An element can be configured to protect against underfrequency, overfrequency, or the
rate of frequency change. Rate of frequency change mode is available only in styles xxExxxxxx of the
DGC-2020HD.
The eight, identical frequency protection elements are designated 81-1, 81-2, 81-3, 81-4, 81-5, 81-6, 81-
7, and 81-8. Element logic connections are made on the BESTlogic
™Plus screen in BESTCOMSPlus®
and element operational settings are configured on the Frequency settings screen in BESTCOMSPlus.
BESTCOMSPlus Navigation Path: Settings Explorer, Generator Protection, Frequency, Frequency (81)
Front Panel Navigation Path: Settings Explorer > Protection > Settings Group x (where x = 0 to 3) >
Frequency Protection > Frequency (81)
Frequency Measurement
For all sensing connections, the frequency is measured through the DGC-2020HD A- and B-phase
sensing voltage connections.
To measure frequency, the voltage sensed by the DGC-2020HD must be greater than 10 Vac. The
measured frequency is the average of two cycles of voltage measurement.
Underfrequency and Overfrequency
Underfrequency and overfrequency protection can be useful for detecting load shedding or islanding. For
example, when a genset is suddenly separated or isolated from the electric utility, the frequency will
change quickly from the nominal values (except for the improbable case of a perfect load-to-generation
match). This makes frequency measurement an excellent method for detecting an island condition.
Any of the eight 81 elements can be configured for underfrequency or overfrequency protection.
Mode
Underfrequency or overfrequency protection is selected through the Mode setting. A setting of Under
selects underfrequency and a setting of Over selects overfrequency protection.
Source
A Source setting configures the frequency element to monitor the generator sensing input terminals or the
bus sensing input terminals.
DGC-2020HD Generator Protection