ABB Relion 620 Series - Page 712

50 Hz
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
49 Hz
ST_FRG
OPR_FRG
500ms
1s
OPERATE is activated
as Freq< AND df/dt
condition satisfied
OPERATE
48.75 Hz
Start of operation timer
ST_FRQ
OPR_FRQ
Start of operation timer
1s
Time [s]
Frequency
[Hz]
Figure 370: Load-shedding operation in the “Freq< AND df/dt>” mode when both
Freq< and df/dt conditions are satisfied ( Rated frequency=50 Hz)
Protection functions
1MRS757644 H
712 620 series
Technical Manual