7SR11 & 7SR12 Commissioning and Maintenance Guide
©2017 Siemens Protection Devices Limited Chapter 6 Page 42 of 72
2.12 Undercurrent (37)
7SR12
46
BC
46
NPS
(x2)
37
(x2)
49
50
BF
51V
V
L1
(V
A
)
V
L2
(V
B
)
V
L3
(V
C
)
I
L1
(I
A
)
81
HBL
2
37
(x2)
49
50
BF
51V
I
L2
(I
B
)
81
HBL
2
37
(x2)
49
50
BF
51V
I
L3
(I
C
)
81
HBL
2
I
4
(I
G
)
74
T/
CCS
NOTE: The use of some
functions are mutually exclusive
67/
50
(x4)
67/
51
(x4)
67/
50N
(x4)
67/
50
(x4)
67/
50
(x4)
67/
51
(x4)
67/
51
(x4)
67/
51N
(x4)
67/
50
SEF
67/
51
SEF
27
59
(x4)
27
59
(x4)
27
59
(x4)
47
(x2)
79
Optional
59N
(x2)
Note:
Example shows
Voltage Config =
Van, Vbn, Vcn
60
CTS
60
VTS
50BF
51c
51c
51c
64H
81
(x4)
37G
(x2)
Figure 2-13 Undercurrent
Voltage Inputs: n/a
Current Inputs: I
L1
(I
A
), I
L2
(I
B
), I
L3
(I
C
),I4
Disable: 51N, 51G, 46, 60CTS, 46BC
Map Pickup LED: 37-n - Self Reset
Undercurrent Guard: As required
Undercurrent start: Any or ALL
If two Undercurrent 37 elements are used with different settings, it is convenient to test the element with the
lowest setting first. The higher setting element can then be tested without interference from the other element.
Apply 3Phase balanced current or single phase current on the single pole relay models and earth fault function
37G/37SEF, at a level above the Undercurrent 37-n setting until the element resets. Check operation with start
option set to ANY phase and repeat with it set to operate for ALL phases.
If DTL setting is small, gradually reduce any phase current in turn until element operates.
If DTL is large apply 1.1x setting, check for no operation, apply 0.9x setting, check operation
Testing of this element phase by phase may cause inadvertent operation of the 46 NPS Overcurrent elements.
Apply 0.5x setting current and record operating time
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