7SR242 Duobias Description Of Operation
©2010 Siemens Protection Devices Limited Chapter 1 Page 41 of 52
3.13 Voltage Protection: Under/Over Frequency (81)
Optionally six under/over frequency elements are provided.
Frequency elements are blocked if the measured voltage falls 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 frequency 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 frequency elements can be inhibited from:
Inhibit 81-n A binary or virtual input.
81-n U/V Guarded Under voltage guard element.
Figure 3-20 Logic Diagram: Under/Over Frequency Detector (81)
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