Inrush Restraint (81Hbl2); Figure 5.8-1 Logic Diagram: Harmonic Block Feature (81Hbl2) - Siemens 7SR21 Manual

5.8

Inrush Restraint (81HBL2)

Inrush restraint detector elements are provided, these monitor the line currents.
The inrush restraint 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 value of the second harmonic component is above the 81HBL2 setting.
81HBL2 Element
Enabled
Disabled

Figure 5.8-1 Logic Diagram: Harmonic Block Feature (81HBL2)

©2010 Siemens Protection Devices Limited
81HBL2 Setting
81HBL2 Bias
c
>
IL1
>
IL2
>
IL3
7SR21 & 7SR22 Argus Description of Operation
L1 81HBL2
L2 81HBL2
L3 81HBL2
Chapter 1 Page 65 of 71