vector group test

8/13/2019 Vector Group Test

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VECTOR GROUP TEST....Q. What is vector group?A. In three phase transformers we can connect the winding in different fashion.Based onthe wingding connection, we will determine vector group.generally vector group is indicated on theName Plate of transformer by the manufacturer.The vector group teaches us about the phase

difference between the primary and secondary sides.The Determination of vector group oftransformers is very important before connecting two or more transformers in parallel.

If two transformers of different vector groups are connected in parallel then phasedifference exist between the secondary of the transformers and large circulating current flowsbetween the two transformers.

PHASE DISPLACEMENTS BETWEEN WINDING'S (PRIMARY & SECONDARY)...Phase Displacement between HV and LV Windings:

The vector for the high voltage winding is taken as the reference vector. Displacement of thevectors of other windings from the reference vector, with anticlockwise rotation, is represented by theuse of clock hour figure.

IS: 2026 (Part 1V)-1977 gives 26 sets of connections star-star, star-delta, and star zigzag,delta-delta, delta star, delta-zigzag, zigzag star, zigzag-delta. Displacement of the low voltage winding

vector varies from zero to -330 in steps of -30, depending on the method of connections.Hardly any power system adopts such a large variety of connections. Some of the commonly usedconnections with phase displacement of 0, -300, -180and -330(clock-hour setting 0, 1, 6 and 11).

some of clock diagrams for vector group of transformers:


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Symbol for the high voltage winding comes first, followed by the symbol of low voltagewinding. For example a 400/132/11 kV Transformer connected star, star and delta and vectors of 132and 11 kV windings having phase displacement of 0 and -330 with the reference (400 kV) vector willbe represented As Yy0 Yd11.

The digits (0, 1, 11 etc) relate to the phase displacement between the HV and LV windingsusing a clock face notation. The phasor representing the HV winding is taken as reference and set at 12oclock. Phase rotation is always anti-clockwise (International adopted).Use the hour indicator as theindicating phase displacement angle. Because there are 12 hours on a clock, and a circle consists out of

360, each hour represents 30.Thus1 = 30, 2 = 60, 3 = 90, 6 = 180 and 12 = 0 or 360.
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Phase Shift (Deg) Connection of winding of transformer

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

APPILICATION OF TRANSFORMER ACCORDING TO VECTOR GROUP:1. Dyn11, Dyn1, YNd1, YNd11
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Common for distribution transformers.

Normally Dyn11 vector group using at distribution system. Because Generating Transformer areYNd1 for neutralizing the load angle between 11 and 1.

We can use Dyn1 at distribution system, when we are using Generator Transformer are YNd11.

In some industries 6 pulse electric drives are using due to this 5thharmonics will generate if weuse Dyn1 it will be suppress the 5th harmonics.

Star point facilitates mixed loading of three phase and single phase consumer connections.

The delta winding carry third harmonics and stabilizes star point potential.

A delta-Star connection is used for step-up generating stations. If HV winding is star connectedthere will be saving in cost of insulation.

But delta connected HV winding is common in distribution network, for feeding motors andlighting loads from LV side.

2. Star-Star (Yy0 or Yy6)

Mainly used for large system tie-up Transformer.

Most economical connection in HV power system to interconnect between two delta systemsand to provide neutral for grounding both of them.

Tertiary winding stabilizes the neutral conditions. In star connected transformers, load can beconnected between line and neutral, only if

(a) the source side transformers is delta connected or

(b) the source side is star connected with neutral connected back to the source neutral.

In This Transformers. Insulation cost is highly reduced. Neutral wire can permit mixed loading.

Triple harmonics are absent in the lines. These triple harmonic currents cannot flow, unlessthere is a neutral wire. This connection produces oscillating neutral.

Three phase shell type units have large triple harmonic phase voltage. However three phasecore type transformers work satisfactorily.

A tertiary mesh connected winding may be required to stabilize the oscillating neutral due tothird harmonics in three phase banks.

3.Delta Delta (Dd 0 or Dd 6)

This is an economical connection for large low voltage transformers.

Large unbalance of load can be met without difficulty.

Delta permits a circulating path for triple harmonics thus attenuates the same.

It is possible to operate with one transformer removed in open delta or V connection meeting58 percent of the balanced load.

Three phase units cannot have this facility. Mixed single phase loading is not possible due tothe absence of neutral.

4 . Star-Zig-zag or Delta-Zig-zag (Yz or Dz)

These connections are employed where delta connections are weak. Interconnection of phases

in zigzag winding effects a reduction of third harmonic voltages and at the same time permitsunbalanced loading.

This connection may be used with either delta connected or star connected winding either forstep-up or step-down transformers. In either case, the zigzag winding produces the same angulardisplacement as a delta winding, and at the same time provides a neutral for earthing purposes.

The amount of copper required from a zigzag winding in 15% more than a corresponding star ordelta winding. This is extensively used for earthing transformer.


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Due to zigzag connection (interconnection between phases), third harmonic voltages arereduced. It also allows unbalanced loading. The zigzag connection is employed for LV winding. For agiven total voltage per phase, the zigzag side requires 15% more turns as compared to normal phaseconnection. In cases where delta connections are weak due to large number of turns and small crosssections, then zigzag star connection is preferred. It is also used in rectifiers.

5. Zig- zag/ star (ZY1 or Zy11)

Zigzag connection is obtained by inter connection of phases.4-wire system is possible on bothsides. Unbalanced loading is also possible. Oscillating neutral problem is absent in this connection.

This connection requires 15% more turns for the same voltage on the zigzag side and hencecosts more. Hence a bank of three single phase transformers cost about 15% more than their 3-phasecounterpart. Also, they occupy more space. But the spare capacity cost will be less and single phaseunits are easier to transport.

Unbalanced operation of the transformer with large zero sequence fundamental mmf contentalso does not affect its performance. Even with Yy type of poly phase connection without neutralconnection the oscillating neutral does not occur with these cores. Finally, three phase coresthemselves cost less than three single phase units due to compactness.

6. Yd5:

Mainly used for machine and main Transformer in large Power Station and Transmission

Substation. The Neutral point can be loaded with rated Current.

7. Yz-5

For Distribution Transformer up to 250MVA for local distribution system.

The Neutral point can be loaded with rated Current.

APPLICATIONS ACCORDING VECTOR GROUP:1. Step up Transformer: It should be Yd1 or Yd11.

2. Step down Transformer: It should be Dy1 or Dy11.

3. Grounding purpose Transformer: It should be Yz1 or Dz11.

4. Distribution Transformer: We can consider vector group of Dzn0 which reduce the 75%of harmonics in secondary side.

5. Power Transformer: Vector group is deepen on application for Example : GeneratingTransformer : Dyn1 , Furnace Transformer: Ynyn0.

PROCEDURE OF DOING TEST:1. Derive the equations according to vector group given on name plate details.

Ex. Dy11


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2. Apply three phase primary winding of 415v, apply only Rphase voltage to secondary winding do notconnect the secondary Y,B phases to any circuit.3. note down the voltages according to the above equations.4.The above equations must satisfy by that respective vector group,depending upon vector groupequations will change.

Q.What is the need of doing this test?A. We just confirming the the vector group given on name plate details is correct or not.

Remove all electrical connections while doing test for better results........
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vector group test

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