ABB RER620, Technical Manual

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Section 4
1MAC309294-MB F
Protection functions
226 RER620
Technical Manual
Start value df/dt setting. The df/dt detection is activated when the frequency gradient
decreases at a faster rate than the set value of Start value df/dt .
The df/dt detection module includes a timer with the DT characteristics. Upon detection
of df/dt, operation timer activates the
ST_FRG
output. When the timer has reached the
value set by Operate Tm df/dt , the
OPR_FRG
output is activated if the df/dt condition still
persists. If df/dt becomes normal before the module operates, the reset timer is activated.
If the reset timer reaches the value of the
Reset delay time setting, the timer resets and the
ST_FRG
output is deactivated.
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.