ST_FRQ
output. When the underfrequency timer has reached the value set by
Operate Tm Freq, the
OPR_FRQ
output is activated if the underfrequency condition
still persists. If the frequency becomes normal before the module operates, the
reset timer is activated. If the reset timer reaches the value set by
Reset delay time,
the timer resets and the
ST_FRQ
output is deactivated.
df/dt detection
The df/dt detection measures the input frequency calculated from the voltage
signal and calculates its gradient. A high df/dt condition is detected by comparing
the gradient to the
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.
1MRS757644 H
Protection functions
620 series
Technical Manual
711
