AC chokes for 3-phase applications

1- and 3-phase AC chokes for line frequencies are also called commutating chokes, line chokes or string chokes. They are used in power electronic circuits between the mains connection and the converter or rectifier input and have alternating current flowing through them.
Due to their inductance, they limit the commutation voltage dips and current peaks on the mains side or the di/dt in the circuit.

Three-phase line chokes are always “open switched”, vector group III”.


Rated variables are the thermal alternating current as well as, as a rule, a, expressed as a percentage of the mains voltage, voltage drop uk at the choke, also called uD or ΔU.
For example, converter manufacturers often demand a short-circuit voltage uk = 4%. If the connection is then made without a transformer, a line choke with uk=4% is used.

Even when operating with a transformer, this may have a short-circuit voltage <4%, depending on the power. In this case, a supplementary line choke can be connected in series. This is individually adapted to the power converter requirement and the transformer short-circuit voltage. Sometimes the supplementary choke is mechanically mounted on the transformer and wired to it. Standard construction specifications for various line currents are available for the typical values uk = 4% and 2%. 3-phase line chokes with uk=4% are partly available from stock.

Unlike with transformers, it is recommended to use string voltages for the voltage specifications.

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If you have any product-specific questions, please contact Thomas Bremer. Together we will answer the last open questions regarding your enquiry.

Dipl.-Ing. Thomas Bremer: 03378 2006-0