All about Star Delta winding connection

What is star and delta connection?

All about star delta winding connection, difference between a star and a delta connection, advantages, disadvantages

There are mainly 2 types of 3 phase winding connection, namely the star or Wye (Y) connection and the delta or D connection.

The Star or Y connection:

If we connect the each end of winding to a common point and The rest of the three points of three windings are connected to the supply , to form a Y shaped 3 phase winding then it is said to be star connected winding. 

Star winding connection diagram, load and phase current, advantages disadvantages and application

The star winding has some special characteristics, these are:

  • In case of star winding each phase winding carries 1/√3 times the phase to phase / line voltage.
  • Each of the winding carries current that is equal to the load current
  • It has a common neutral point , and so that it can supply 3 phase as well as single phase load
  • Generally it is the distribution part

* Here the term 'phase current/voltage' means the current/voltage that is flowing through each of the winding and the term load current/ voltage stands for the current/voltage that is applied across the load or supply terminal
The Delta or D connection:

In case of delta connection we connect each of winding end to the consecutive start of next winding, and the winding then looks like  a Delta. The supply voltage is given to each of the joining point of winding

Delta winding connection diagram, load and phase current, advantages disadvantages and application

The delta winding has some special characteristics , these are:

  • The delta winding has the same phase to phase voltage and line voltage ie, the voltage across each winding is equal to the applied voltage.
  • The phase current is 1/√3 times that of the load/line current
  • It has active noise cancellation properties
  • Generally it is at the transmission end

Difference between the star and delta winding:

The difference between the star and delta winding is as follows

  • Star winding has phase current = line current where as the delta winding has  line current = √3 phase current
  • The star connected winding has line voltage = √3 phase voltage but the delta winding has line voltage = phase voltage.
  •  The star winding has a common neutral point but the delta winding does not have any neutral point.
  • In case any one of the supply phase is absent or out of order, The delta winding can supply 3 phase load with the remaining two phases with reduced load ( this type of connection is called open delta or v connection) but the star winding cant supply the three phase load with any of the phase out of order.
  • We can feed single phase load from the star connected winding with the help of neutral wire but in case of  delta winding cant feed single phase load

Application and uses of star delta connection:

Both the winding connection is employed in t three phase motor and transformer because of their specific advantages.

  1. In case of star star delta starter the stator winding of the motor is first connected to the star connection and then in the delta connection, the reason behind doing so, the star winding has reduced winding voltage compared to the line voltage , which helps to reduce the starting current taken by the motor but the motor is shifted to delta in running condition to provide full load voltage to the armature and to develop rated torque.
  2. The distribution transformer are mostly provided with Dyn type of winding, that means it takes input with the delta winding ( the transmission end) and supplies the load with the star winding. This is done due to the reason that the delta winding has effective noise cancellation properties and the star winding can provide neutral point to supply single phase load.

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