Voltage Protection: Under/Over Frequency (81); Figure 3.13-1 Logic Diagram: Under/Over Frequency Detector (81) - Siemens 7SR224 Description & Operation

3.13 V P
OLTAGE
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
81-n U/V Guarded
©2009 Siemens Protection Devices Limited
: U
ROTECTION NDER
A binary or virtual input.
Under voltage guard element.

Figure 3.13-1 Logic Diagram: Under/Over Frequency Detector (81)

/O F (81)
VER REQUENCY
(1) Description of Operation 7SR224
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