Transformer winding connection

When we want to install the transformer for our project or any application and auto transformer stater,firstly we must know the transformer winding connection.If not it will cause the damage or serious injury when it install with wrong connection.

So how we can identify the transformer winding connection?Here i want share some tips how to identify the winding connection.This basic information can effected to our voltage supply and if not done i  proper way,it can cause serious damage to our application or equipment.

Commonly manufacture already setting their code or identification method using a letters and numbers.Below is a standard identification code for transformer winding connection for USA,UK and EUROPE :-

What is transformer winding connection?



1) The high voltage (HV) terminals

It commonly have upper-case letters e.g. A-B-C, R-Y-B, U-V-W, L1-L2-L3


2) The low voltage (LV) terminals

Its commonly have lower-case letters e.g :  a-b-c, r-y-b, u-v-w, l1-l2-l3


High and Low voltage numbering

Each winding has a start numbered 1 and a finish numbered 2.Tapping are numbered 3, 4, 5 etc  from the start terminal.The choice of letters and numbers tends to be a national preference.

The type of winding is given a letter, again upper case for HV and lower case for LV windings.For more detail please refer for the example below :-

  • Y for Star HV, y for star LV
  • D for Delta HV, d for delta LV
  • Z for Zig-zag HV, z for zig-zag LV

Since a phase angle displacement can occur across the transformer due to its method of connection it is necessary to identify.

The numbering system for this is based on the hands of a clock. Each five-minute position on a clock gives 30◦ phase displacement hence,

  • 12 o’clock gives zero displacement
  • 1 o’clock gives −30◦ displacement
  • 6 o’clock gives 180◦ displacement
  • 11 o’clock gives +30◦ displacement


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