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.
1MRS759142 F
Protection functions
REX640
Technical Manual
931