ABB 615 Series ANSI, Техническое руководство

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1MAC050144-MB C
Section 4
Protection functions
615 series ANSI 271
Technical Manual
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
Pickup value df/dt setting.The df/dt detection is activated when the frequency gradient
decreases at a faster rate than the set value of Pickup 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
Trip Tm df/dt, the OPR_FRG output is activated if the df/dt condition still
persists. If df/dt becomes normal before the module trips, 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 PICKUP and TRIP output
signals are activated.
When the PICKUP output is active, the percentage of the elapsed delay time can be
monitored through PICKUP_DUR which is available as monitored data.