Delta-Star Connection of Transformer – Three-Phase Transformer Connection

Digital ElectronicsElectronElectronics & Electrical

In case of the delta-star connection of a 3-phase transformer, the primary winding is connected in delta while the secondary winding is connected in star (see the figure).

  • Primary Winding − As the primary winding is connected in delta. Hence, the line voltage and the phase voltage on the primary side are the same and the line current is √3 times of the phase current.

  • Secondary Winding − The secondary winding is connected in star fashion. Thus, the secondary line voltage is √3 times of the phase voltage and the line current is equal to the phase current.

The delta-star connected 3-phase transformers are mainly used to step-up the voltage, i.e., at the beginning of the high voltage transmission system.

In case of the delta-star connection, the secondary phase voltages lead the primary phase voltages by +30° and this is also the phase relationship between the line voltages.

Advantages of Delta-Star Connection

The following are principle advantages of the delta-star connection of the transformers −

  • The delta connected primary winding requires less area of cross-section.

  • The secondary winding is star connected and the neutral is present. Thus it can be used for 3-phase, 4-wire system.

  • There is no distortion in the secondary voltage due to third harmonic component.

  • This connection can handle unbalanced loads.

  • The relaying of the ground fault protection is very easy in case of delta-star connection.

Disadvantages of Delta-Star Connection

The main disadvantage of the delta-star connection is that the secondary voltage and the primary voltage are not in phase with each other. Therefore, it is not possible to operate the delta-star connected transformer in parallel with the delta-delta or star-star connected transformers.

Applications of the Delta-Star Connection

The delta-star connection of the transformers is mainly used in the following applications −

  • The delta-star connection is used in step-up transformers, where neutral at the secondary side is required.

  • The delta-star connected transformers are mainly used as generator transformer for connecting the generators to the transmission system.

  • They are also used in industrial, commercial and high-density residential distribution systems.

raja
Published on 12-Aug-2021 12:29:32
Advertisements