Siemens Reyrolle 7SR45 Argus Device Manual page 94

Applications
5.2 Current-Transformer Requirements and Sample Calculations
Case 2
Fault current = 20 A
[fo_ALF_V4, 1, --_--]
R = 0.49 at 20 A (Refer to impedance graphs for current > 1 A (rated current, I
b
ALF ≥ 6.6
The typical accuracy limit factor is ALF = 10.
This calculation is an example. To select an appropriate CT, calculate with the actual parameters.
Recommended CTs
Considering the CTs are connected to the 7SR45 Argus Relay only and the distance between CTs and the
7SR45 Argus relay (typically 3 m) is short, use the following CTs:
•
2.5 VA, 5P10 or 5P20 for I
•
2.5 VA, 5P20 for I
NOTE
i
i
For safe operation of the 7SR45 Argus Relay, the maximum power delivered to the relay is 1000 VA for 1 s.
Moreover, Siemens does not recommend overloading the relay above 1000 VA for multiple times.
For more information, refer to Thermal Withstand in Electrical Tests under Technical Data chapter in the Hard-
ware Manual.
94
= 1 A
rated
= 5 A
rated
= 1 A))
rated
Reyrolle, 7SR45, Device Manual
C53000-G7040-C101-2, Edition 09.2020