ABB RELION Series Technical Manual page 452

Section 4
Protection functions
446
Frequency
[Hz]
50 Hz
49 Hz
ST_FRG
Start of operation timer
OPR_FRG
OPERATE
GUID-DB333B09-D987-4A62-ABAE-7B70ACA275EB V2 EN
Figure 227: Load-shedding operation in the "Freq< AND df/dt>" mode when only
the df/dt condition is satisfied (Rated frequency=50 Hz)
Restore detection
If after the activation of the OPERATE input the frequency recovers to a level above
the Restore start Val setting, the RESTORE signal output is activated. The RESTORE
output remains active for a 100 ms. The Restore mode setting is used to select the
restoring mode to be "Disabled", "Auto" or "Manual".
Start value Freq set at 0.975 xFn
Start value df/dt set at -0.020 xFn/s
Operate Tm df/dt = 500ms
Operate Tm Freq = 1000ms
Load shed mode = Freq< AND df/dt
1s
500ms
OPERATE is not
activated in this case
as Freq< condition not
satisfied
1MRS758755 A
Time [s]
REC615 and RER615
Technical Manual