Once the frequency has stabilized, LSHDPFRQ can restore the load that is
shed during the frequency disturbance. The restoration is possible manually or
automatically.
The function contains a blocking functionality. It is possible to block function
outputs, timers or the function itself, if desired.
4.6.2.4 Operation principle
The function can be enabled and disabled with the
Operation
setting. The
corresponding parameter values are "On" and "Off".
The operation of LSHDPFRQ can be described using a module diagram. All the
modules are explained in the next sections.
Figure 369: 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
Protection functions
1MRS757644 H
710 620 series
Technical Manual
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