Zigzag circuit

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The zigzag connection (English: three-phase-inter-star or zig-zag ) is used for load distribution on the low-voltage side of three-phase AC transformers for feeding low-voltage networks. It can be viewed as a combination of star and delta connection and is identified in the vector group with the letter "z".

function

Symbols
Equivalent circuit diagram of a transformer with high voltage side in star and low voltage side in zigzag connection with vector group Yzn11

With this type of connection, as with the star connection, two voltages (e.g. 230/400 V) are present at the output, since it also has a star point tap, but it tolerates unbalanced loads like a delta connection.

With delta and star connections, the individual windings are only ever on one leg. With the zigzag connection, however, the windings are divided into two equal parts. Two of the winding parts are distributed over two legs. In this way, an asymmetrical load on the secondary side is better distributed to the outer conductor on the primary side. The single-phase current flow on the secondary side generated by the unbalanced load is distributed over two legs, and thus on two outer conductors on the primary side.

This advantage is paid for by the following disadvantages:

  • You need about 15% more copper.
  • More copper leads to greater winding losses.
  • Because of the higher losses, transformers with this type of connection are only available up to 400 kVA.
  • The production of a transformer with the zigzag circuit is more complex.

In principle, a double zigzag circuit is also possible. Because of the zigzag switching on the primary and secondary side, the material and manufacturing costs are increased and the switching is at best interesting for special cases. If you choose a suitable vector group (not Zz0 or ZNzn0), windings on all three legs of the transformer are involved in the energy transfer with single-phase load. In this case, the amounts of the currents on the supply lines form the ratio 2: 1: 1.

use

The zigzag circuit is used in three-phase transformers with a highly asymmetrical load, e.g. B. in transformers to supply emigrant farms .

Footnotes

  1. ^ Silicon Rectifier Handbook , Motorola Inc. 1973, p. 78
  2. ^ Friedrich Electrical Engineering Tables , Verlag Dümmler, Bonn 1982, pp. 7-27, ISBN 3-427-53021-3