WAZIPOINT Engineering Science & Technology: Delta-Wye Connection of Transformers

## 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

 Connection Phase Voltage Line Voltage Phase Current Line Current Star VP = VL ÷ √3 VL = √3 × VP IP = IL IL = IP Delta VP = VL VL = 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 the line voltage divided by root three; similarly, in the delta connection, the phase current is equal to the line current divided by root three.

### Delta-Star Turns Ratio

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

The ratio is the relationship between the number of primary winding turns to the number of secondary winding turns—and thus a comparison between the primary phase voltage and the secondary phase voltage. For typical delta/delta systems, the ratio is 2:1—but for typical delta/wye systems, the ratio is 4:1.

### Advantages of Delta-Star Connected Transformer

-On the primary side due to the 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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