A three-phase generating set can be connected in Y (star) or in Δ delta. The difference lies in the connection of the windings. If the generating set is connected in star, there are two possible voltages: phase voltage (V_P = 230V) and line voltage (V_L = 400V). ‘I_L’ stands for line current and ‘I_P’ stands for phase current. We can say that V_L = √3*V_P en I_P = I_P. If the generating set is connected in delta, the line voltage V_L equals the phase voltage V_P and I_L = √3*I_P.
Besides, the star configuration has 4 wires: 3 phase wires and 1 neutral wire starting from the star point. The delta configuration on the other hand, has no neutral wire.
 
Star:
V_Line = √3*V_Phase
I_Line = I_Phase


V_L1  = V_F1  - V_F2
V_L2  = V_F2  - V_F3
V_L3  = V_F3  - V_F1
V_L1  + V_L2  + V_L3  = 0
V_L1  = 2*V_F1*cos 30° = 2*V_F1*√3/2 = √3*V_F1
 
The line voltage leads the phase voltage by 30°.
The line currents equal the phase currents with symmetrical charges.
The active power when connected in Y: P = 3*(V_L/√3)*I_L*cos φ = √3*V_L*I_L*cos φ
 
Delta:
V_Line = V_Phase
I_Line = √3*I_Phase

 
Ī_L1 = Ī_P1 - Ī_P1
Ī_L2 = Ī_P2 - Ī_P3
Ī_L3 = Ī_P3 - Ī_P1
Ī_L1 + Ī_L2 + Ī_L3 = 0
I_L1 = 2*I_P1*cos 30° = 2*I_P1*3/2 = √3*I_P1
 
The line current leads the phase current by 30°.
The line voltages equal the phase voltages with symmetrical charges.
The active power when connected in Δ: P = 3*VL*(IL/√3)*cos φ = √3*VL*IL*cos φ