24 March 2018

Zig zag Transformer : Advantages, Application

  • 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 600 phase displacement in the zig zag connection. The vector sum of these windings is 86.6% of the line to neutral voltage.

       Triangle ABC
       AC2 = AB2 + BC2 – 2 ( AB )( BC ) Cos θ
              = ( a / 2 )2 + ( a / 2 )2 – 2 ( a / 2 ) ( a / 2 ) Cos 1200
              = ( a2 / 4 ) + ( a2 / 4 ) – ( a2 / 2 ) Cos ( 900 + 300 )
              = ( a2 / 2 ) + ( a2 / 2 ) Sin 300
              = ( a2 / 2 ) + ( a2 / 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 1200 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 1200 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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