Significance of Vector Group of Transformer - your electrical guide

Hi friends, in this article, I am going to describe the significance of vector group of transformer. It is very essential information for parallel operation of transformers and is very interesting also.

The internal connections of transformer windings can be made in a number of ways. Accordingly, different types of connections have been standardized depending upon the phase displacement.

There are four vector groups and each group includes three methods of connection of high voltage and low voltage windings.

Phase displacement between EMFs of high voltage and low voltage windings is expressed as the clock hour number and is designated by symbols 0, 6, 1, and 11.

For example, the clock hour number 0 represents zero degrees phase displacement between primary and secondary EMFs. The clock hour number 6 is for 1800 phase displacement,  1 for  – 300, 11 for +300.

# Significance of Vector Group of Transformer

On the nameplate of three-phase transformer vector group is printed as Yy0, Dd1 etc. Here Yy0 will mean it’s both the windings are star-connected and phase displacement between primary and secondary EMFs is zero degree. It is belonging to Group No.1 (refer to table).

 Group No. Winding Connection (Primary) Winding Connection (Secondary) Phase Displacement Clock – Hour Number Vector Symbol 1 Star Delta Delta Star Delta Zig-zag 0o 0 Yy0 Dd0 Dz0 2 Star Delta Delta Star Delta Zig-zag 180o 6 Yy6 Dd6 Dz6 3 Delta Star Star Star Delta Zig-zag – 30o 1 Dy1 Yd1 Yz1 4 Delta Star Star Star Delta Zig-zag +30o 11 Dy11 Yd11 Yz11

Similarly, Dy1 will mean its primary winding is connected in delta, secondary winding in the star, phase displacement is – 300 and belonging to Group No. 3.

Information of vector group of a transformer is very significant when it has to operate in parallel.  For a transformer working in isolation, the arrangement of its internal connections is of little importance.

Transformers will operate in parallel satisfactory if they have,

• the same primary and secondary voltages
• the same tap ratio
• the same percentage impedance, and,
• belonging to the same vector groups.

The two transformers may have their windings connected in star/star and yet it will not be possible to operate in parallel if one belongs to Group 1 and the other to group 2, unless the internal connections of the secondary winding of one of the transformers are changed.

## Transformer | Objective Type Question Answers

### #1 In a transformer, the magnetic coupling between primary and secondary circuit can be increased by

using the magnetic core of low reluctance

### #2 If the flux density in the core of a transformer is increased

size of transformer can be reduced

### #3 At no load, the current taken by a transformer

lags behind the applied voltage by 80 degree

50

400 kVA

### #6 In a power transformer

low voltage winding is closer to core

### #7 If the supply frequency is increased keeping voltage constant

eddy current losses will remain unchanged

### #8 At no load, the current taken by a transformer

lags behind the applied voltage by 80 degree

### #9 Leakage flux of a transformer may be minimized by

sectionalizing and interleaving the primary and the secondary windings

### #11 In a transformer it is difficult to measure the efficiency by output-input measurement method because

efficiency of transformer is usually high and hence extremely accurate measurements will be necessary

0.4 webers/m^2

180 degree

### #15 The desireable properties of transformer core material is

high permeability and low hysteresis loss

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Categories: Transformer