Siemens 7SR242 Duobias - 2.7 Undercurrent (37, 37 G)

7SR242 Duobias Commissioning & Maintenance Guide
©2010 Siemens Protection Devices Limited Chapter 6 Page 34 of 57
2.7 Undercurrent (37, 37G)
Figure 2-9 Undercurrent
Voltage Inputs: n/a
Current Inputs: W1-I
L1
(I
A
), W1-I
L2
(I
B
), W1-I
L3
(I
C
), I
G1
or W2-I
L1
(I
A
), W2-I
L2
(I
B
), W2-I
L3
(I
C
), I
G2
Disable: 50N, 51N, 51G, 46, 87BD
Map Pickup LED: 37-n, 37G-n - Self Reset
2.7.1 37-n Elements
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.
These elements can be allocated to W1 or W2 current inputs by relay settings, ensure that current is injected on
the correct input.
Apply 3P balanced current at a level above the 37-n setting until the element resets.
If DTL setting is small, gradually reduce any each 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 these elements phase by phase may cause inadvertent operation of the 46 NPS Overcurrent elements.