Vector groupFrom Wikipedia, the free encyclopedia

In electrical engineering, a vector group is the International Electrotechnical Commission (IEC) method of

categorizing the primary and secondary winding configurations of three-phase transformers . It indicates the

windings configurations and the difference in phase angle between them. For example, star(H.V)-delta(L.V) 30

degree lead is denoted as Yd11.

The phase windings of a polyphase transformer can be connected internally in different configurations,

depending on what characteristics are needed from the transformer. For example, in a three-phase power

system, it may be necessary to connect a three-wire system to a four-wire system, or vice versa. Because of

this, transformers are manufactured with a variety of winding configurations to meet these requirements.

Different combinations of winding connections will result in different phase angles between the voltages on the

windings. This limits the types of transformers that can be connected between two systems, because

mismatching phase angles can result in circulating current and other system disturbances.

[edit]Symbol designationThe vector group provides a simple way of indicating how the internal connections of a particular transformer

are arranged. In the system adopted by the IEC, the vector group is indicated by a code consisting of two or

three letters, followed by one or two digits. The letters indicate the winding configuration as follows:

D: Delta winding, also called a mesh winding. Each phase terminal connects to two windings, so the

windings form a triangular configuration with the terminals on the points of the triangle.

Y: Wye winding, also called a star winding. Each phase terminal connects to one end of a winding, and the

other end of each winding connects to the other two at a central point, so that the configuration resembles

a capital letter Y. The central point may be connected outside of the transformer.

Z: Zigzag winding, or interconnected star winding. Basically similar to a star winding, but the windings are

arranged so that the three legs are "bent" when the phase diagram is drawn. Zigzag-wound transformers

have special characteristics and are not commonly used where these characteristics are not needed.

III: Independent windings. The three windings are not interconnected inside the transformer at all, and

must be connected externally.

In the IEC vector group code, each letter stands for one set of windings. The HV winding is designated with a

capital letter, followed by medium or low voltage windings designated with a lowercase letter. The digits

following the letter codes indicate the difference in phase angle between the windings, with HV winding is taken

as a reference. The number is in units of 30 degrees. For example, a transformer with a vector group of Dy1

has a delta-connected HV winding and a wye-connected LV winding. The phase angle of the LV winding lags

the HV by 30 degrees.

Phase displacement

Phase rotation is always anti-clockwise. (international adopted convention) Use the hour indicator as the

indicating phase displacement angle. Because there are 12 hours on a clock, and a circle consists out of 360°,

each hour represents 30°. Thus 1 = 30°, 2 = 60°, 3 = 90°, 6 = 180° and 12 = 0° or 360°. The minute hand is set

on 12 o'clock and replaces the line to neutral voltage (sometimes imaginary) of the HV winding. This position is

always the reference point. Because rotation is anti-clockwise, 1 = 30° lagging (LV lags HV with 30°)and 11 =

330° lagging or 30° leading (LV leads HV with 30°)

The point of confusion is in how to use this notation in a step-up transformer. As the IEC60076-1 standard has

stated, the notation is HV-LV in sequence. For example, a step-up transformer with a delta-connected primary,

and star-connected secondary, is not written as 'dY11', but 'Yd11'. The 11 indicates the LV winding leads the

HV by 30 degrees.

Transformers built to ANSI standards usually do not have the vector group shown on their nameplate and

instead a vector diagram is given to show the relationship between the primary and other windings.

Transformer vector groupUnderstanding vector groups:

The vector groups are used for three phase transformers for representing their winding connections. Let us assume the following winding connections:

 Now we have to find vector group of the above transformer. The currents on primary side are IA, IB, IC and currents on secondary side

are Ia, Ib, Ic. Now let us assume currents in

secondary windings are ia', ib', ic'. so

Ia= ia'-ib'

Now representing this in vector form (vector displacement of ib' is 120 deg from ia') :

So, Ia is derived in above figure. As Ia is leading IA by 30 deg. the vector group is

d11. Phase rotation is always anti-clockwise. (international adopted convention)

See the vector groups below:

In the vector group: First symbol/symbols, capital letters: HV winding connection.Second symbol/symbols, small letters: LV winding connection.

Third symbol, number: Phase displacement expressed as the clock hour number.

Winding connection designations:High Voltage Always capital lettersDelta - DStar - YInterconnected star - ZNeutral brought out - N

Low voltage Always small lettersDelta - dStar - yInterconnected star - zNeutral brought out - n

For auto transformer - a

Phase displacement: Phase rotation is always anti-clockwise. (international adopted convention)Use the hour indicator as the indicating phase displacement angle. Because there are 12 hours on a clock, and a circle consists out of 360°, each hour represents 30°.Thus 1 = 30°, 2 = 60°, 3 = 90°, 6 = 180° and 12 = 0° or

360°.The minute hand is set on 12 o'clock and replaces the line to neutral voltage (sometimes imaginary) of the HV winding. This position is always the reference point.Because rotation is anti-clockwise, 1 = 30° lagging (LV lags HV with 30°)and 11 = 330° lagging or 30° leading (LV leads HV with 30°)

To summarise:Dd0 : Delta connected HV winding, delta connected LV winding, no phase shift between HV and LV.Dyn11 : Delta connected HV winding, star connected LV winding with neutral brought out, LV is leading HV with 30°YNd5 : Star connected HV winding with neutral brought out, delta connected LV winding, LV lags HV with 150°YNa0d11 : Star connected HV winding with neutral brought out, auto transformer with 0° displacement. LV winding delta conected leading HV by 30°

The phase-bushings on a three phase transformer are marked either ABC, UVW or 123 (HV-side capital, LV-side small letters). Two winding, three phase transformers can be devided into four main categories (Clock hour number and phase displacement of those

most frequently encountered in practice in brackets)

Group I - (0 o'clock, 0°) - delta/delta, star/starGroup II - (6 o'clock, 180°) - delta/delta, star/starGroup III - (1 o'clock, -30°) - star/delta, delta/starGroup IV - (11 o'clock, +30°) - star/delta, delta/star

(Minus indicates LV lagging HV, plus indicates LV leading HV)

Group IExample: Dd0 (no phase displacement between HV and LV)The conventional method is to connect the red phase on A/a, Yellow phase on B/b, and the Blue phase on C/c. Other phase displacements are possible with unconventional connections (for instance red on b, yellow on c and blue on a) By doing some unconventional connections externally on one side of the trsf, an internal connected Dd0 transformer can be changed either to a Dd4(-120°) or Dd8(+120°) connection. The same is true for internal connected Dd4 or Dd8 transformers.Group IIExample: Dd6 (180° displacement between HV and

LV)By doing some unconventional connections externally on one side of the trsf, an internal connected Dd6 transformer can be changed either to a Dd2(-60°) or Dd10(+60°) connection.Group IIIExample: Dyn1 (-30° displacement between HV and LV)By doing some unconventional connections externally on one side of the trsf, an internal connected Dyn1 transformer can be changed either to a Dyn5(-150°) or Dyn9(+90°) connection.Group IVExample: Dyn11 (+30° displacement between HV and LV)By doing some unconventional connections externally on one side of the trsf, an internal connected Dyn11 transformer can be changed either to a Dyn7(+150°) or Dyn3(-90°) connection.

what the difference between transformer Dyn11 and Dyn1

According to most standards transformer coils are classed as either Delta (D), Wye (Y) or Zigzag (Z).

Dy11 signifies a Delta Primary (primary has an upper case letter), Wye secondary (secondary has a lower case letter) and the orientation of the 3 phase diagram, relative to the A phase on a clock face pointing to 11 o'clock.

So draw 3 vectors 120 degrees apart to represent the 3 phases, but start with your

reference phase (A phase) at 11 o'clock.

Dy1 would hence be a Delta primary, Wye secondary and a vector diagram with the reference vector pointing at 1 o'clock.

I believe most 3 phase textbooks have the vector diagram with the reference vector at 0 degrees on the x-axis, which would equate to 3 o'clock, then with B at 11 o'clock and C at 7 o'clock.

but what according to what in the first place we choose Dyn1 or Dyn11

Any combination of a Delta coil and a Wye coil (Dy or Yd) will cause a phase shift by +/- 30 degrees. Therefore we use another Delta coil and Wye coil combo to shift it back to whatever is desired.

And yes, if you want to parallel transformers they have to be of the same vector group or you will have circulating currents and associated problems.

Vector Groups

Transformer nameplates carry a vector group reference such at Yy0, Yd1, Dyn11 etc.  This relatively simple nomenclature provides important information about the way in which three phase windings are connected and any phase displacement that occurs.

Winding ConnectionsHV windings are designated:   Y, D or Z (upper case)LV windings are designated:    y, d or z (lower case)

Where:Y or y indicates a star connectionD or d indicates a delta connectionZ or z indicates a zigzag connectionN or n indicates that the neutral point is brought out

Phase DisplacementThe digits ( 0, 1, 11 etc) relate to the phase displacement between the HV and LV windings using a clock face notation.  The phasor representing the HV winding is taken as reference and set at 12 o'clock.  It then follows that:

Digit 0 means that the LV phasor is in phase with the HV phasorDigit 1 that it lags by 30 degreesDigit 11 that it leads by 30 degreesetc

All references are taken from phase-to-neutral and assume a counter-clockwise phase rotation.  The neutral point may be real (as in a star connection) or imaginary (as in a delta connection)

When transformers are operated in parallel it is important that any phase shift is the same through each.  Paralleling typically occurs when transformers are located at one site and connected to a common busbar

(banked) or located at different sites with the secondary terminals connected via distribution or transmission circuits consisting of cables and overhead lines 

Basic TheoryAn ac voltage applied to a coil will induce a voltage in a second coil where the two are linked by a magnetic path.  The phase relationship of the two voltages depends upon which way round the coils are connected.  The voltages will either be in-phase or displaced by 180 deg as below:

 

In phase 180deg displacement

When 3 coils are used in a 3 phase transformer winding a number of options exist.  The coil voltages can be in phase or displaced as above with the coils connected in star or delta and, in the case of a star winding, have the star point (neutral) brought out to an external terminal or not.

Example -  Dyn11We now know that this transformer has a delta connected primary winding (D) a star connected secondary (y) with the star point brought out (n) and a phase shift of 30 deg leading (11).  Connections and vector diagrams are as follows::

   HV

   LV

Other ConfigurationsBy connecting the ends of the windings in other ways a wide range of options becomes available as set out below.

Phase shift (deg) Connections

0 Yy0 Dd0 Dz0

30 lag Yd1 Dy1 Yz1

60 lag Dd2 Dz2  120 lag Dd4 Dz4  150 lag Yd5 Dy5 Yz5

180 lag Yy6 Dd6 Dz6

150 lead Yd7 Dy7 Yz7

120 lead Dd8 Dz8  60 lead Dd10 Dz10  30 lead Yd11 Dy11 Yz11

End

What is vector group dyn11 in transformer?In: Electrical Engineering [Edit categories]

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Answer:Vector group means it defines the primary & secondary side connection type of the transformer. It says D for the delta connections (windings connected between two phases) & Y for the star

connections (windings connected from each phase to ground). The 11 stands for the phase displacement of the secondary referenced to the primary. Imagine a clock with only an hour hand; at 11 o'clock, the hand is at 30 degrees to the reference (12 c'clock), so the secondary is at 30 degrees to the primary. 

D or d means delta connection Y or y means star/wye connection z means zed/zigzag/interconnected star connection N or n means the Neutral point is accessible in the

star connection. This is also sometimes taken to mean that the neutral point is earthed.

A number means a phase shift in the secondary with respect to the primary, where the phase is measured in "hours"

A capital letter indicates primary winding and lower case secondary. Capital z does not occur as zed transformers are used only for creating an earth on an unearthed system and thus are always on the earthed secondary.

Primary is taken to be the higher voltage side, regardless of the direction of power flow.

So, Dyn11 means delta primary, star

secondary leading the primary by 30 degrees, possibly with an earthed neutral

Answer:How to test the Transformer Vector Group at Site? 

This vector group test is done at site to check if their is any damage in the windings during transportation and erection. 3 -phase AC supply is given on HV side. R-Phase HV and r-phase LV shorted. 

Then to qualify the test following conditions are to be satisfied after measurement of voltages. 

nR+nY=RY, By>> Bb and Yb=Yy.

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