ABB RELION Series Technical Manual page 451

1MRS758755 A
REC615 and RER615
Technical Manual
Load-shedding control
The way of load-shedding, that is, whether to operate based on underfrequency or high
df/dt or both, is defined with the Load shed mode user setting. The valid operation
modes for the Load shed mode settings are "Freq<", "Freq< AND df/dt" and "Freq<
OR df/dt".
Once the selected operation mode conditions are satisfied, the START and OPERATE
output signals are activated.
When the START output is active, the percentage of the elapsed delay time can be
monitored through START_DUR which is available as monitored data.
Frequency
[Hz]
50 Hz
49 Hz
48.75 Hz
ST_FRG
Start of operation timer
OPR_FRG
ST_FRQ
OPR_FRQ
OPERATE
GUID-143A36EB-FCC9-4E87-B615-7743A3D75A15 V2 EN
Figure 226: Load-shedding operation in the "Freq< AND df/dt>" mode when both
Freq< and df/dt conditions are satisfied (Rated frequency=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
1s
500ms
Start of operation timer
OPERATE is activated
Section 4
Protection functions
Time [s]
1s
as Freq< AND df/dt
condition satisfied
445