Voltage Selection
The largest magnitude phase to neutral voltage is selected as the source for df/dt measurement based on
fundamental frequency DFT measurement.
When a phase is selected it will continue to be used unless the voltage falls below the minimum threshold of
30 V rms using fundamental frequency DFT. If the selected voltage falls below the minimum threshold, the
source will change to the highest phase to neutral voltage from the other 2 phase to neutral values. The
frequency measurement will be continuous and any element that is picked up will be unaffected.
Logic of the Function
[lo_7SR5_81Rlogicdiagram, 1, en_US]
Figure 5-53
Logic Diagram: 81R Frequency Protection – "df/dt"
Application and Setting Notes
Parameter: Element
•
Default setting: Disabled
This setting is used to allow the element to be switched on and off if it is not required. A separate setting
is provided for each element. These setting can be used to select the number of elements required.
Parameter: Setting
•
Default setting: 0.1 Hz/s
This is the operating frequency threshold of the element. If the element is underfrequency, the element
will pickup if the frequency falls below this value. If the element is overfrequency, the element will
pickup if the frequency rises above this value. This should be set to suit the individual application.
5.28.3
5.28.4
Protection and Automation Functions
5.28 81R Frequency Protection – "df/dt"
Reyrolle 7SR5, Overcurrent Protection Device, Device Manual 351
C53000-G7040-C014-1, Edition 11.2019
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