Wiring
3.3 Current transformer selection data
Analog input module AI Energy Meter 480VAC/CT HF (6ES7134-6PA00-0CU0)
Manual, 07/2018, A5E42674880-AA
27
Current transformer connection requirements
DIN VDE 0100-557 and IEC 60364-5-55 require the following for the connection of current
transformers:
● The secondary circuits of current transformers must not be grounded.
● Guards must not be used in the secondary circuits of current transformers.
● The insulation of the secondary cables of transformers must be designed for the highest
voltage of all active components, or the secondary cables must be installed in such a way
that their insulation cannot touch any active components, such as busbars.
● Connection points must be provided for temporary measurements.
Current transformer selection data
Introduction
Connection via a current transformer is always required for the current measurement. Use
toroids with an accuracy class of 0.5, 1 or 3.
Dimensioning of the current transformer
The correct dimensioning of the current transformer is important for the following reasons:
● You achieve correct results from the measurements and
● You do not overload or damage the current transformers.
Selecting a current transformer
Use current transformers with a burden capacity 1.5 to 2 times greater than the power
dissipation in the terminal circuit (consisting of resistance of the connection cables and
burden of the AI Energy Meter HF). 1.5 times the power loss is required in order to prevent
the transformer from overloading. 2 times the power dissipation is important to ensure the
current limiting in case of a short-circuit.
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