7SR224 Argus Description of Operation
3.13 Voltage Protection: Under/Over Frequency (81)
Four under/over frequency elements are provided.
The relay utilises fundamental voltage measurement values for this function. The frequency calculation is based
on the highest input voltage derived from the voltage selection algorithm.
Frequency elements are blocked if all phase voltages fall below the
81 U/V Guard
setting.
The sense of the element (under-frequency or over-frequency) is set by the
81-n Operation
setting.
81-n Setting
sets the pick-up voltage level for the element.
An output is given after elapse of the
81-n Delay
setting.
The
81-n Hysteresis
setting allows the user to vary the pick-up/drop-off ratio for the element.
Operation of the under/over voltage elements can be inhibited from:
Inhibit 81-n
A binary or virtual input.
81-n U/V Guarded
Under voltage guard element.
Figure 3.13-1
Logic Diagram: Under/Over Frequency Detector (81)
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Chapter 1 Page 38 of 70