ABB RELION 620 Series Technical Manual page 338

Section 4
Protection functions
332
Frequency
[Hz]
60 Hz
58.8 Hz
ST_FRG
Start of operation timer
OPR_FRG
TRIP
GUID-DD22BDCD-1B89-4370-81D2-8F032EE4C08A V3 EN
Figure 149: Load-shedding operation in the "Freq< AND df/dt>" mode when only the
df/dt condition is satisfied (Rated frequency=60 Hz)
Restore detection
If after the activation of the TRIP input the frequency recovers to a level above the Restore
pickup 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".
Pickup value Freq set at 0.975 xFn
Pickup value df/dt set at -0.020 xFn/s
Trip Tm df/dt = 500ms
Trip Tm Freq = 1000ms
Load shed mode = Freq< AND df/dt
1s
500ms
TRIP is not activated
in this case as Freq<
condition not satisfied
1MAC504801-IB E
Time [s]
620 series ANSI
Technical Manual