Chapter 1) 7SR242 Duobias Description Of Operation
©2015 Siemens Protection Devices Limited
Chapter 1 Page 50 of 60
5.3 Inrush Detector (81HBL2)
Inrush detector elements monitor the line currents.
The inrush detector can be used to block the operation of selected elements during transformer magnetising
inrush conditions.
The
81HBL2 Bias
setting allows the user to select between
Phase
,
Sum
and
Cross
methods of measurement:
Phase
Each phase is inhibited separately.
Sum
With this method the square root of the sum of the squares of the second harmonic in each
phase is compared to each operate current individually.
Cross
All phases are inhibited when any phase detects an inrush condition.
An output is initiated where the measured ratio of second harmonic to fundamental current component content is
above the
81HBL2
setting. An LED assigned to this function operates instantaneously, whereas an output relay
assigned to this function operates after a 60ms time delay.
Figure 5-4 Logic Diagram: Inrush Detector Feature (81HBL2)
Summary of Contents for 7SR242 Duobias
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