Siemens Reyrolle 7SR46 - Inrush Detector (81 HBL2)

Inrush Detector (81HBL2)
The inrush detector (81HBL2) element detects the presence of high levels of 2
nd
harmonic current, which indi-
cates a transformer inrush current during switch-on. The inrush current raises above the operate level of the
overcurrent elements for a short duration. It is important that the relay does not issue an incorrect trip
command for this transient network condition.
If a magnetic inrush condition is detected, then operation of the overcurrent elements can be blocked.
The calculation of the magnetizing inrush current level is complex, however a ratio of 20% of the 2
nd
harmonic
to the fundamental current meets most applications without compromising the integrity of the overcurrent
protection.
When the inrush detector (81HBL2) is active, if the current crosses the 81HBL2 Release Block setting,
then the relay issues the trip command and provides the fault and event records based on the protection func-
tion I
s
setting and the current magnitudes.
i
i
NOTE
When the 50LC Inrush Action is enabled, the 81HBL2 Release Block setting must be greater than
the 50LC Setting.
5.6
Applications
5.6 Inrush Detector (81HBL2)
78 Reyrolle, 7SR46 Device, Manual
C53000-G7040-C103-1, Edition 10.2022