Vector group

When switching group in which is electrical energy technology in three-phase transformers the connection of the upper and lower voltage side coils in a three-phase alternating current system , respectively. The top indicates the side of the transformer with higher electrical voltage , the bottom with lower voltage. Depending on the vector group, there are also different transmission ratios between the top and bottom in addition to the number of turns. The specification takes place in DIN VDE 0532 , among others .

General

Scheme of a three-phase transformer

A three-phase transformer has three wound iron legs. In simple transformers with a high-voltage and a low-voltage three-phase system, each leg carries one high-voltage and one low-voltage winding. The transformer thus has a total of six windings. The vector group specifies the interconnection of the three associated windings of a three-phase system.

The top and bottom of the three-phase transformer can be divided into a basic circuit, with each side independently of the other side can take one of the following forms:

With the star connection , abbreviated with the letter “Y” or “y”, the beginnings of the three windings are connected to the outer conductors of the external three-phase system. The ends are connected together and form the star point . Depending on the application and system, the star point is, for example, rigidly earthed as part of the star point treatment and connected to an existing neutral conductor , or connected to the earth fault compensation .

In the delta connection , abbreviated with the letter "D" or "d", the three windings are connected in series, i.e. H. the end of one winding is connected to the beginning of the next winding. The corner points of the resulting triangle are connected to the outer conductors of the three-phase system. There is no star point.

With the zigzag circuit , abbreviated with the letter "Z" or "z", each winding of a three-phase system encloses two iron legs halfway. The beginnings of the windings are connected to the three outer conductors, the ends are connected to a star point. The zigzag connection of the windings usually only takes place on the low voltage side. As an alternative to the zigzag connection, compensating windings are used.

In the special case of the autotransformer (autotransformers), abbreviated by the letter "a" represents the low-voltage winding part of the high-voltage winding represents. Autotransformers for three-phase alternating current are performed in the star circuit, the phase shift between upper and lower voltage side is 0 °.

In addition, there is a phase shift in the external conductor voltages within the framework of a vector group . As a result, the transformation ratio of three-phase transformers takes on a complex value .

Identification of the vector group

The vector group and its identification consists of the following points:

Circuit type of the high-voltage side system. Capital letters are used, see above. The alternative identifier "III" indicates that the beginning and end of the winding of the three windings are routed separately to the outside. If the star point of the system on the high voltage side is accessible, this is indicated by an "N".
Connection type of the low-voltage side system. Lower case letters are used, see above, the alternative identifier "iii" is also possible.
Specification of the phase shift. The phase shift between the high and low voltage side is specified as a multiple of 30 ° in the form of a code, the so-called hourly number. Depending on the combination of the switching type of high voltage and low voltage, the possible values are either all six even digits 0,2,4,6,8 or 10 or all odd digits 1,3,5,7,9 or 11 the even digits phase shifts of 0 °, 60 °, 120 °, 180 °, 240 ° or 300 ° and for the odd digits phase shifts of 30 °, 90 °, 150 °, 210 °, 270 °, 330 °. There is no circuit in which all twelve multiples of the phase shifts are possible. Since the voltage on the low voltage side follows that of the high voltage side , mathematically working with a negative sign. In other words, the number of hours is actually a multiple of -30 ° .

If a transformer has several undervoltage systems, e.g. B. three-winding transformer, further information on the connection is added according to the same pattern.

In the case of transformers for single-phase alternating current , the alternative identifier "Ii0" or, rarely, "Ii6" is sometimes specified as the vector group, whereby only these vector groups are possible.

Special vector groups, for example the machine transformers in the Freudenau power station , have four windings with the vector group "YNd5d5d5". On the low-voltage side, this means three winding groups in a triangle, which lead to the three individual generators . The power plant has a total of six generators. On the high-voltage side, the machine transformer has a star connection to the high-voltage network with a phase rotation of 150 ° and a star point brought out for the purpose of star point connection.

Examples

The following table gives examples of some common vector groups, their complex voltage translation and applications. Here, w ₁ denotes the number of turns on the upper voltage side and w _{2 on} the lower voltage side.

Vector group	Voltage transmission	description	application
YNyn0	${\ displaystyle {\ underline {\ ddot {u}}} = {\ frac {w_ {1}} {w_ {2}}}}$	Star connection on the high and low voltage side with external star points	Large coupling transformers in the network and parallel operation, e.g. B. between 380 kV and 220 kV level.
Yd5	${\ displaystyle {\ underline {\ ddot {u}}} = {\ frac {{\ sqrt {3}} \ cdot w_ {1}} {w_ {2}}} \ cdot e ^ {j \ cdot 150 ^ {\ circ}}}$	High voltage side star, low voltage side delta connection	Machine transformer
Yd11	${\ displaystyle {\ underline {\ ddot {u}}} = {\ frac {{\ sqrt {3}} \ cdot w_ {1}} {w_ {2}}} \ cdot e ^ {j \ cdot 330 ^ {\ circ}}}$	High voltage side star, low voltage side delta connection	Machine transformer
Dy5	${\ displaystyle {\ underline {\ ddot {u}}} = {\ frac {w_ {1}} {{\ sqrt {3}} \ cdot w_ {2}}} \ cdot e ^ {j \ cdot 150 ^ {\ circ}}}$	High-voltage side delta, low-voltage side star connection	Distribution transformers of small to large power
Yz5	${\ displaystyle {\ underline {\ ddot {u}}} = {\ frac {2 \ cdot w_ {1}} {{\ sqrt {3}} \ cdot w_ {2}}} \ cdot e ^ {j \ cdot 150 ^ {\ circ}}}$	High-voltage side star, low-voltage side zigzag connection	Small distribution transformer for heavily asymmetrical loads.

Various vector groups and their circuits

literature

Adolf J. Schwab: Electrical energy systems - generation, transport, transmission and distribution of electrical energy . Springer, 2006, ISBN 3-540-29664-6 .
Siemens AG, Power Transmission and Distribution Transformers Division (Hrsg.): Three-phase distribution transformers . Company publication, 2006 ( online (PDF; 495 kB)).