7SR18 Commissioning & Maintenance Guide
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3.9 THERMAL OVERLOAD (49)
46
BC
46
NPS
(x2)
37
(x2)
49
50
BF
I
L1
(I
A
)
81
HBL
2
37
(x2)
49
50
BF
I
L2
(I
B
)
81
HBL
2
37
(x2)
49
50
BF
I
L3
(I
C
)
81
HBL
2
I
4
(I
G
)
74
T/
CCS
NOTE: The use of some
functions are mutually exclusive
50
(x2)
51
(x2)
50N
(x2)
50
(x2)
50
(x2)
51
(x2)
51
(x2)
51N
(x2)
50G
(x2)
51G
(x2)
60
CTS
50BF
51c
51c
51c
Figure 3.9-1 Thermal Overload
Current Inputs: I
L1
(I
A
), I
L2
(I
B
), I
L3
(I
C
),
Disable: 51, 50, 37, 50CBF
Map Pickup LED: 49Alarm
The current can be applied from a 3P balanced supply or phase by phase from a 1P supply. Alternatively the 3
phase current inputs can be connected in series and injected simultaneously from a single 1P source.
The Thermal Overload Setting and Time Constant Setting can be considered together to calculate the operating
time for a particular applied current.
The following list below shows operate times for a range of Time Constant Settings for an applied current of 2x
the Thermal Overload setting. Ensure that the thermal rating of the relay is not exceeded during this test.
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