7SR242 Duobias Description Of Operation
©2010 Siemens Protection Devices Limited Chapter 1 Page 46 of 52
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 given where the measured ratio of second harmonic to fundamental current component content is
above the 81HBL2 setting.
Figure 5-4 Logic Diagram: Inrush Detector Feature (81HBL2)
5.4 OverFluxing Detector (81HBL5)
Overfluxing detector elements monitor the line currents.
The over fluxing detector can be used to block the operation of differential protection (87BD/ 87HS) elements.
The 81HBL5 Bias setting allows the user to select between Phase, Sum and Cross methods of measurement:
Phase Each phase is inhibited separately
Sum The inrush current from each phase is summated and compared to each operate current
individually
Cross All phases are inhibited when any phase detects an inrush condition
An output is given where the measured fifth harmonic component content is above the 81HBL5 setting.
IL1
IL2
IL3
81HBL5 Bias
L2 81HBL5
81HBL5 Setting
c
>
>
>
L1 81HBL5
L3 81HBL5
81HBL5 Element
Enabled
Disabled
>
1
81 HBL5
Figure 5-5 Logic Diagram: Overfluxing Detector Feature (81HBL5)
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