Delta-Wye Connection of Transformers


Delta-Star Connection of Transformer

Delta-Star or Delta-Way Connection of Transformers

Delta-star or Delta-Way connected transformers are mainly used in power distribution or near before consumer end. 

Delta-Star transformer uses the Delta connection of its primary coils where the balanced load is supplied from the utility company. 

On the other hand, secondary coils are connected as a star or Y form where there is a chance of an unbalanced load. 

The secondary windings provide the required 4th-wire neutral or earth connection for using a single phase or three-phase load.

Three-phase Voltage and Current

ConnectionPhase VoltageLine VoltagePhase CurrentLine Current
VP = VL ÷ √3
VL = √3 × VP
IP = IL ÷ √3
IL = √3 × IP

In the star connection line current and phase current are the same; similarly, in the delta connection, the line voltage is equal to the phase voltage.

In the star connection phase voltage is equal to line voltage divided by root three; similarly, in the delta connection, the phase current is equal to line current divided by root three.

Delta-Star Turns Ratio

delta-star turns ratio

TR= Turn Ratio
Np= Primary turn
Ns= Secondary turn
Vp= Primary Voltage
Vs= Secondary voltage

Advantages of Delta-Star Connected Transformer

-On the primary side due to delta connection and winding cross-section required is less.

-On the secondary side, neutral is available, which can be used for a 3-phase, 4-wire supply system.

-No distortion due to third harmonic components.

-Large unbalanced loads can be handled without any difficulty.

-Assuming that the neutral of the Y-connected secondary circuit is grounded, a load connected phase-to-neutral or a phase-to-ground fault produces two equal and opposite currents in two phases in the primary circuit without any neutral ground current in the primary circuit.

The disadvantage of the Delta-Star Transformer

In the Delta-Star Transformer connection, the secondary voltage is not in phase with the primary voltage. 

So,  it is not possible to operate the Delta-Star Transformer connection in parallel with the star-star or the delta-delta connected transformer.

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