3.14 Voltage Protection: Under/Over Frequency (81) - 7Sr22; Figure 3.14-1 Logic Diagram: Under/Over Frequency Detector (81) - Siemens 7SR21 Manual

3.14 Voltage Protection: Under/Over Frequency (81) – 7SR22
Six under/over frequency elements are provided in the 7SR22 relay.
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 frequency elements can be inhibited from:
Inhibit 81-n
81-n U/V Guarded

Figure 3.14-1 Logic Diagram: Under/Over Frequency Detector (81)

©2010 Siemens Protection Devices Limited
7SR21 & 7SR22 Argus Description of Operation
A binary or virtual input, or function key.
Under voltage guard element.
Chapter 1 Page 47 of 71