Wiring
3.3 Current transformer selection data
Analog input module AI Energy Meter 480VAC ST (6ES7134-6PA20-0BD0)
Manual, 12/2015, A5E36061895-AA
23
Example: Usage of a current transformer 500/5 A
You use a current transformer with a transmission ration of 500/5 A that has a rated burden
Z
n
of 5 VA according to the data sheet.
The maximum primary current in the application amounts to 400 A. This means that the
maximum secondary current I
max.
amounts to 4 A. The burden of the AI Energy Meter
including connection resistance amounts to R
Burden
= 25 mΩ.
The maximum value of the resistance of the connection cable (outgoing and incoming line) is
obtained using the following formula:
The maximum cable resistance between the transformer and the terminals of the Energy
Meter may not exceed 287.5 mΩ in this case. The corresponding cable length (outgoing and
incoming line) depends on the cross-section used of the copper line and can be determined
by using the following table.
The following table shows the resistance values of copper cables for typical cross-sections
with ρ = 0.017857 Ω x mm
2
/m
Estimating the length for a connection cable
The value in the table must be less than the calculated terminal resistance R
L
max
of the
cable. For the resistance R
Lmax
of 287.5 mΩ used in the above example it is possible to use a
connection cable (outgoing and incoming line) with a length of 10 m from a cross-section of
0.75 mm
2
upward.
Cable overview for copper
2
2
2
2
2
2
2
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