7SR10 Description of Operation
©2018 Siemens Protection Devices Limited Chapter 1 Page 47 of 77
3.4.12 Voltage Protection: Under/Over Frequency (81)
Four under/over frequency elements are provided in the 7SR1004 relay –
81-1, 81-2, 81-3 & 81-4.
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.
The relay utilises fundamental frequency RMS voltage for this function. All under/over frequency elements have a
common setting to measure phase to phase
(Ph-Ph)
or phase to neutral
(Ph-N)
voltage using the
Frequency
Input mode
setting.
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 is inhibited when Vph < 35V (Frequency Input Mode = Ph- Ph) or
Vn < 35V (Frequency Input Mode = Ph- N) and from:
Inhibit 81-n
A binary or virtual input, or function key.
81-n U/V Guarded
Under voltage guard element.
or
> <
General Pickup
81-n
Inhibit 81-n
81-n Hysteresis
81-n Delay
c
&
81-n Setting
81-n Operation
81-n Element
Enabled
Disabled
81-n U/V Guarded
Yes
&
Voltage
Selection
VL1
VL2
VL3
F
<
&
81 U/V Guard
Setting
<
<
Figure 3-26 Logic Diagram: Under/Over Frequency Detector (81)
Summary of Contents for 7SR10 Argus Series
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