Vector group

As the switching group, the interconnection of the upper and lower voltage windings is referred to in a three- phase AC system in electrical power engineering in three phase transformers. The upper side indicates the side of the transformer with a higher electrical voltage, the bottom with a lower voltage. Depending on the switching group are listed in addition to the turns ratio different ratios between top and bottom. The specification takes place in DIN VDE 0532nd

General

A three phase transformer has three wound iron legs, which in the simplest embodiment of the transformer - each bearing an upper and a lower voltage winding - with only one above and one low side phase current system. The transformer thus has a total of six windings. The three belong together windings of a three-phase system can be interconnected in different ways, which is specified in the form of different vector groups.

Each side of the three-phase transformer can be initially divided into the following basic circuits, each page can be independent from the other side take one of the following forms:

• In the star connection, abbreviated by the letter "Y" or "Y", the beginnings of the three windings are connected to the outer conductors of the outer three-phase system, connected together, the ends to form a star point. The star point is grounded, for example, depending on the application and system in the context of the neutral-point rigid and, if present, is connected to the neutral conductor, or connected to the earth fault.
• In delta connection, abbreviated to the letter "D" or "D", the three windings connected in series, that is, the end of one winding is connected to the beginning of the next winding. The vertices of the resulting triangle are connected to the outer conductors of three-phase system. A neutral point does not exist.
• Wherein the zigzag circuit, abbreviated to the letter "Z" or "Z", encloses each winding of a three-phase system rather than a single leg of iron, but is applied to each of two iron legs in half. The beginnings of the windings are connected to the three phase conductors, the ends are in turn interconnected to form a star point.
• For the special case of autotransformer ( auto-transformers ), in which the low-voltage winding is a part of the high-voltage winding, the letter "a" is used. Auto-transformers for three-phase alternating current can be carried out in the star circuit, the phase shift between the upper and lower voltage side is 0 °.

In addition, results in the context of a vector group, a phase shift of the phase voltages. Thus, the ratio of three-phase transformers assumes complex value.

The switch group and their markings shall consist of the following points:

If a transformer multiple low voltage systems, eg Three-winding transformer, so more information will be added in connection with the same arguments.

Examples

In the following table are examples of some common switching groups, given their complex voltage translation and applications. It refers to the above - w1, w2 the unterspannige turns.

For transformers for single-phase is sometimes referred to as switching group " Ii0 " or rarely " ii6 ", with only these switching groups are possible.

Special switching groups, such as the machine transformers in the power plant Freudenau, have four windings of the switching group " YNd5d5d5 ". This means on the low voltage side winding three groups in the triangle, leading to the three individual generators. The power plant has a total of six generators. On the high voltage side of the generator transformer has a star connection for high voltage power to a phase shift of 150 ° and brought out the star point in order Sternpunktverschaltung.