Electrical Engineering ⇒ Topic : Star-Star Connection

Star-Star Connection

Figure (a) shows the star-star connection which is economical for small and high voltage transformers because the phase voltage is (1/√3) times of the line voltage and hence the number of turns per phase and quantity of insulation required is minimum. There is a phase shift of 30⁰ between the phase voltages and line voltages on both the primary and secondary whereas the line voltages both in the primary and secondary are in phase with each other shown in Figure (b).

                   Figure (a) Star-star connection.                                  Figure (b) Phasor diagram of star-star connection

The ratio of voltages on the primary and secondary sides is equal to the transformation ratio of each transformer. The star-star connection works well for balanced load. If the load is unbalanced, the neutral shifts. To prevent this, star point of the primary is required to be connected to the star point of the generator