Method of 3 Phase Transformer Connection-Electronicsinfos

3-Phase Transformer Connection

    There are Different Connections used in 3-phase transformers to connect their windings that are described below

    Method of Three phase transformer connection

    • Star-Star or Y-Y Connection
    • Delta-Delta or Δ-Δ Connection 
    • Star-Delta or Y-Δ Connection 
    • Delta-Star or Δ-Y Connection 

    Star-Star Connection

    Star-Star is a type of Three-phase winding connection in which both primary and Secondary windings are connected in a Star connection. Star-star connections work better on the balance load. In this type of Connection, Both Sides of the Neutral are on Earth. Star-Star Connection is Suitable For Low Current and High Voltage Transformers. The line current and phase current are equal in the star-star connection. The Other Name of Star-Star Connection is called Y-Y Connection.

    Y-Y Connection.


    • We need a Less Number of Turns because Voltage is Reduced 1/√3 so Copper Saving is possible.
    • We need less space due to the less insulation Required.
    • There is No phase Displacement In primary and Secondary Windings so we can easily operate transformers in parallel.
    • we Obtain 3 Phase 4 wire Systems in star-star connection.


    • if we do not connect the primary neutral to the source, unbalanced conditions happen so the result is neutral floating.
    • Transformer obtained a Third harmonic magnetic Current so the result is Distorted emf is produced if we do not connect the primary neutral to the generator neutral.


    Delta-Delta Connection is a three-phase winding connection in which both primary and secondary windings are in the delta connection. This connection is mostly suitable for low voltages. The Line voltages and phase voltages are equal in the Delta-Delta connection. The Relation between phase current and line current is

    Delta-Delta Connection


    This System is used where we require low voltage and high current.


    • In the Delta-Delta connection phase, the current is reduced by 1/√3 of the line current so the cross-sectional area is reduced and conductor saving is possible.
    • The third harmonic is easily passed in the Delta-Delta Connection so we obtained sinusoidal voltages.
    • Unbalance load is Not affecting the Delta-Delta connection.
    • There is no phase Displacement in primary and secondary windings.
    • if one phase is not provided supply the other is operated in a full load of 57.7%.

    • In the Delta-Delta connection, there are no neutral wires so we did not obtain a three-phase 4-wire system.
    • we need a high value of insulation because line voltage is equal to phase voltage.


    Star-Delta is a Three phase winding connection in which primary winding is connected to the star and secondary winding is connected to the delta connection. Star-Delta connections are mostly used in substations end of transmission lines where we step done the voltage. In this connection, we connect primarily to neutral earth. The Transformation ratio of Secondary and primary line voltage is 1/√3 times. The phase Displacement from Primary to secondary is 30૦.



    Delta-Star Is a type of three-phase connection in which primary winding is connected in delta and secondary winding is connected in star connection. Delta-Star connections are mostly used where we need to step up the voltage for example H.T. Transmission system. Delta-Star connections are most frequently used because we operate Three phase lighting circuit.

    Delta-Star Connection

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