ABB RELION Series, Technical Manual

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GUID-17F7A604-487F-4D45-8150-AE041BB939B1 V2 EN
Figure 225: 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
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.
Section 4
1MRS758755 A
Protection functions
444 REC615 and RER615
Technical Manual