Vector Group Of Transformer

The vector group represents the phase difference between the primary side and the secondary side, which is introduced due to the specific configuration of the transformer winding connection. Before connecting two or more transformers in parallel, it is very important to determine the vector group of the transformers.

What Is Vector Group Of Transformer

Basically, the transformer vector group is used to find the arrangement of the high-voltage and low-voltage windings of a three-phase transformer. Three-phase transformers can have a variety of wiring methods, and the wiring method of the transformer is determined by its vector group.

The vector group of the transformer depends on the following factors:
Removal of harmonics: The star winding of the three-phase transformer is used to reduce the third harmonic.
Parallel operation: In parallel operation, the vector group and polarity of all transformers should be the same.

Three-phase transformer windings can have multiple connections, and the winding connection determines the vector group of the transformer. The vector group represents the phase difference between the primary side and the secondary side, which is introduced due to the specific configuration of the transformer winding connections. Before connecting two or more transformers in parallel, it is very important to determine the vector group of the transformers. If two transformers with different vector groups are connected in parallel, there will be a phase difference between the secondary transformers, and a large circulating current will flow between the two transformers, which is very unfavorable.

Types Of Vector Group Of Transformer

The connection of all windings in a three-phase transformer is represented by vector group symbols. This symbol uses a numeric index to indicate the winding connection and its relative phase shift.
The numeric index of the vector group comes from the clock hour of the high voltage winding (1U) phase voltage pointer (2U) at 12 o'clock. The phase sequence of the system should be 1U, IV, 1W or R, S, T.
The following are the most common three-phase connections: Dd0, Dyn5, Dyn11, Yyn0, Yd1, Yd11, Dz0, Yz1, and Yz11.

Significance Of Vector Group In 3 Phase Transformer

The star or delta windings of a three-phase transformer can be connected in six different ways. In order to perform parallel operation of transformers without looking at the winding connection, the manufacturer mentioned vector grouping of transformers to avoid accidental failures.

It also indicates how the windings of the transformer and the end connections of the windings are connected to the output terminals.

Yy0, Dd1, etc. are printed on the nameplate of the three-phase transformer vector group. Here Yy0 means that the windings are all star-connected, and the phase shift between the primary and secondary electromotive force is zero degrees. It belongs to the first group
In the same way, Dy1 means that the primary winding is delta connection, and the secondary winding is star connection, with a phase shift of -300, which belongs to the third group.

When transformers need to be operated in parallel, the vector group information is very important. For an isolation transformer, the arrangement of its internal connections is not important.

If the transformers meet the following conditions, they will operate in parallel satisfactorily,
1. The primary and secondary voltages are the same
2. The same tap ratio
3. The same percentage impedance, and,
4. Belong to the same vector group.
The windings of two transformers can be connected in star/star, but if one belongs to group 1 and the other group belongs to group 2, it cannot be operated in parallel unless the internal wiring of the secondary winding of one of the transformers is changed.

Vector Group Of Transformer Calculations

The representation method of the connection group of the transformer is: uppercase letters indicate the connection mode of the primary side (or primary side), and lowercase letters indicate the connection mode of the secondary side (or secondary side). Y (or y) is star connection, D (or d) is delta connection. The number uses clock notation to indicate the phase relationship between the primary and secondary side line voltages. The primary side line voltage phasor is used as the minute hand, fixed at the 12 o'clock position of the clock, and the secondary side line voltage phasor is used as the hour hand.
There are 4 basic connection types for transformer wiring: "Y, y", "D, y", "Y, d" and "D, d". Our country only uses "Y, y" and "Y, d". Since there are two types of Y connection with neutral line and without neutral line, without neutral line, no symbol is added, and with neutral line, the letter n is added after the letter Y.

1. Use the phase voltage vector diagram to draw the wiring diagram of Y/△ connection
First draw the three-phase voltage vectors A, B, and C of the primary side, using the primary side A-phase voltage as the reference, and rotate clockwise to the required connection group.
2. Use the phase voltage vector diagram to identify the connection group of Y/A connection
3. Use the phase voltage vector diagram to draw the wiring diagram of the △/Y connection
First draw the three-phase voltage vector diagram of the secondary side a, b, and c, and take the secondary side a-phase voltage vector as the reference, rotate counterclockwise to the required connection group, and then draw the wiring diagram of the group according to this vector diagram .
4. Use the phase voltage vector diagram to identify the connection group of △/Y connection
First draw a vector diagram based on the three-phase voltage of the secondary side a, b, and c, and then according to the connection of the primary side winding, just draw the A phase on the secondary side vector, and rotate the primary side A phase clockwise to the secondary side. What is the angle between the side a phase, you know which group the △/Y wiring diagram belongs to.

Selection Of Transformer Vector Group

The transformer vector group depends on
Eliminate harmonics:
Dy connection-y winding eliminates the 3rd harmonic to prevent reflections on the triangle side.

Parallel operation:
All transformers should have the same vector group and winding polarity.
Ground fault relay: Dd transformer has no neutral wire. To limit ground faults in such systems, we can use a sawtooth winding transformer to create a neutral wire together with a ground fault relay.

Non-linear load type:
The system has different types of harmonic and nonlinear loads. For example, we can use Dyn11, Dyn21, Dyn31 to configure the furnace temperature, VFDS, etc., which is 30 degrees. The voltage deviation makes the third harmonic in the power supply system zero.

Transformer application type:
Generally used for power output transformers, that is, delta wiring on the generator side and star wiring on the load side. For imported transformers with power output, that is, in power transmission applications, some people may prefer star-connected transformers, because this can avoid generator-side grounding transformers and save neutral wire insulation. Most systems operate in this configuration. It may be less harmful than operating the delta system incorrectly. The Yd or Dy connection is the standard connection for connecting all units to the generator. There are many factors related to the transformer connection that may be useful for designing the system, so the application of these factors determines the best choice of the transformer.