Advantages of star-star connection in 3-ф transformers: 1. It is possible to use the transformer for 3-phase, four wire system because of neutral. 2. The phase shift between primary and secondary emfs is zero. 3. As phase current equal line current, windings have to carry large currents; hence can be used for supplying large load currents. 4. As phase voltage is 1/root 3 times line voltage, the no.of turns required for primary and secondary are less, hence economical.