Magnetising Inrush Detector (81Hbl2) - Siemens 7SR242 Duobias Technical Manual

3.3

Magnetising Inrush Detector (81HBL2)

Voltage Inputs:
Current Inputs:
Disable:
Map Pickup LED:
Logical operation of the harmonic blocking can be tested by injection of 2
relay) to cause operation of the blocking signals. Note that injection of any level of 2
current input will cause the block to be raised if the Cross or Phase blocking method is used since the harmonic
content on this input is 100%, i.e. greater than setting. Full wave rectified current contains mostly 2
and is the traditional method to generate it without advanced equipment.
If the Cross or Sum Blocking methods are used, fundamental frequency current can be injected into the other
winding simultaneously to operate protection elements if required to test the blocking operation. Care should be
taken that the thermal limits of the relay are not exceeded during these tests.
More advanced test equipment is required, with the facility to combine harmonic and fundamental frequencies of
current, to test the accuracy of setting for current level of the blocking element. Note that the 81HBL2 Setting is
set as a fraction of the total current. e.g. 0.25A at 100Hz combined with 1A at 50Hz gives a 2
of 0.2 i.e. (0.25/(0.25+1.0)).
©2015 Siemens Protection Devices Limited
Chapter 6) 7SR242 Duobias Commissioning & Maintenance Guide
Figure 3-3 Magnetising Inrush Detector
n/a
W1-I (I ), W1-I (I ), W1-I
L1 A L2 B
(I ), or W2-I (I ), W2-I
L3 C L1 A L2
nd
harmonic current (at 100Hz for 50Hz
(I ), W2-I (I )
B L3 C
nd
harmonic alone on a
nd
harmonic
nd
harmonic content
Chapter 6 Page 54 of 62