Voltage Protection: Under/Over Frequency (81) - 7Sr1705/6; Figure 3-22 Logic Diagram: Under/Over Frequency Detector (81) - Siemens 7SR17 Rho Manual

3.9 V P
OLTAGE
Two under/over frequency elements are provided
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 frequency 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
Gn 81-n Element
Enabled
Inhibit 81-n
81-n U/V Guarded
yes
81-n U/V Guard
Setting
<
<
<
VL1
PH-PH
VL2
Or
PH-N
VL3
Voltage
Input Mode

Figure 3-22 Logic Diagram: Under/Over Frequency Detector (81)

©2014 Siemens Protection Devices Limited
: U /O
ROTECTION NDER
A binary or virtual input.
Under voltage guard element.
&
&
&
Chapter 1) 7SR17 Rho Description Of Operation
F (81) - 7SR1705/6
VER REQUENCY
Gn 81-n Operation
Gn 81-n Setting
Gn 81-n Hysteresis
En
> or <
General Pickup
81-n Delay
81-n
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