- It is also called as interconnected star connection. The characteristic of zig zag connection is combined characteristics of star and delta connection.
- There are six windings in the three cores and each core consists of two winding which has equal number of turns.
- Fig A. shows star connection in which each phase consists of two windings. In order to convert this winding into zig – zag connection.

The R1 winding
of the R phase is connected to Y2 winding of Y phase.

The Y1 winding
of the Y phase is connected to B2 winding of B phase.

The B1 winding
of B phase is connected to R2 winding of R phase.

- Each half
winding has 60
^{0}phase displacement in the zig zag connection. The vector sum of these windings is 86.6% of the line to neutral voltage.

Triangle ABC

AC

^{2}= AB^{2}+ BC^{2}– 2 ( AB )( BC ) Cos θ
= ( a / 2 )

^{2}+ ( a / 2 )^{2}– 2 ( a / 2 ) ( a / 2 ) Cos 120^{0}
= ( a

^{2 }/ 4 ) + ( a^{2 }/ 4 ) – ( a^{2 }/ 2 ) Cos ( 90^{0}+ 30^{0})
= ( a

^{2 }/ 2 ) + ( a^{2 }/ 2 ) Sin 30^{0}
= ( a

^{2 }/ 2 ) + ( a^{2 }/ 4 )
AC = √ 3 ( a ) /
2

= 0.866 a

= 86.6 % ( a )

- We can say that 15 % more turns requires for normal line to neutral voltage.
- When three phase currents are in phase and its magnitudes are equal, the ampere turns of R2 phase winding cancelled the ampere turns of B1 phase winding.
- The ampere turns of Y2 phase winding cancelled ampere turns of R1 phase winding.
- The ampere turns of B2 phase winding cancelled the ampere turns of Y1 phase winding.
- This will result in three phase in phase current flows through line to neutral.
- When three phase
currents are equal in magnitude and 120
^{0}phase displacement with respect to each other, the winding ampere turns are not cancelled out therefore the current does not flow through transformer winding only magnetizing current flows through winding. - Therefore in phase current flows through zig zag
transformer winding but 120
^{0}out of phase current does not flows through it.

### Advantages

- It provides neutral connection for delta connected transformer and trap third harmonic current through phase winding.
- The cost of zig zag transformer is less than that of scott transformer and star – delta transformer.
- The application of delta – zig zag transformer is similar to that of star – star and delta – delta transformer because there is not phase shift between primary and secondary winding.
- The zig zag transformer is effective than the star connected transformer and its internal impedance is low.

### Applications

- The star – zig zag transformer or delta – zig zag transformer is used for single phase low voltage application.
- It is also used as grounding transformer because in phase current flows through it.

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