a Three 277120V single phase transformers are connected toge

a) Three 277/120V single phase transformers are connected together to form a wye-delta transfomer. If 320V are applied to the primary, what is the secondary phase voltage?

b) Three 277/120V single phase transformers are connected together to form a delta-delta transfomer. If 320V are applied to the primary, what is the secondary line voltage?

Solution

3-phase 4-wire Wye (i.e., having Y-shaped loads and phases): This load configuration has 3 “current carriers” (aka “lines” or “phases”) which are 120º apart in phase. The fourth conductor is the “neutral” wire, which carries little or no current if the 3 phases are balanced (matched) in load. This 208Y/120 (aka 120/208Vac or 208Y/120 Wye ) configuration is common in the US. The 208 L-L rms voltage value (voltage across any 2 “lines”) derives from VL-N3=1203. There is no Earth Ground here.

same for 320 v also

The 240V Split Phase Delta (aka dog leg or stinger leg) is one of several possible Delta load configurations (named for the delta or triangular shape of the loads and phases). Delta configurations are less common than Wye. There is no Neutral. One load is center tapped to provide two phases with 120Vac and a High Leg which provides 208Vac in addition to 240 Vac.