ABB RED615 Technical Manual page 511

1YHT530004D05 D
615 series
Technical Manual
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.
Section 4
Protection functions
505