Siemens 7SR242 Duobias - 3.3 Magnetising Inrush Detector (81 HBL2)

7SR242 Duobias Commissioning & Maintenance Guide
©2010 Siemens Protection Devices Limited Chapter 6 Page 50 of 57
3.3 Magnetising Inrush Detector (81HBL2)
Figure 3-3 Magnetising Inrush Detector
Voltage Inputs: n/a
Current Inputs: W1-I
L1
(I
A
), W1-I
L2
(I
B
), W1-I
L3
(I
C
), or W2-I
L1
(I
A
), W2-I
L2
(I
B
), W2-I
L3
(I
C
)
Disable:
Map Pickup LED:
Logical operation of the harmonic blocking can be tested by injection of 2
nd
harmonic current (at 100Hz for 50Hz
relay) to cause operation of the blocking signals. Note that injection of any level of 2
nd
harmonic alone on a
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
nd
harmonic
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
nd
harmonic content
of 0.2 i.e. (0.25/(0.25+1.0)).