ABB RED615 Technical Manual page 510

Section 4
Protection functions
504
GUID-17F7A604-487F-4D45-8150-AE041BB939B1 V2 EN
Figure 263: Functional module diagram
Underfrequency detection
The underfrequency detection measures the input frequency calculated from the
voltage signal. An underfrequency is detected when the measured frequency drops
below the set value of the Start Value Freq setting.
The underfrequency detection module includes a timer with the definite time (DT)
characteristics. Upon detection of underfrequency, operation timer activates the
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
1YHT530004D05 D
615 series
Technical Manual